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Hudetz AG. Microstimulation reveals anesthetic state-dependent effective connectivity of neurons in cerebral cortex. Front Neurosci 2024; 18:1387098. [PMID: 39035779 PMCID: PMC11258030 DOI: 10.3389/fnins.2024.1387098] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2024] [Accepted: 06/07/2024] [Indexed: 07/23/2024] Open
Abstract
Introduction Complex neuronal interactions underlie cortical information processing that can be compromised in altered states of consciousness. Here intracortical microstimulation was applied to investigate anesthetic state-dependent effective connectivity of neurons in rat visual cortex in vivo. Methods Extracellular activity was recorded at 32 sites in layers 5/6 while stimulating with charge-balanced discrete pulses at each electrode in random order. The same stimulation pattern was applied at three levels of anesthesia with desflurane and in wakefulness. Spikes were sorted and classified by their waveform features as putative excitatory and inhibitory neurons. Network motifs were identified in graphs of effective connectivity constructed from monosynaptic cross-correlograms. Results Microstimulation caused early (<10 ms) increase followed by prolonged (11-100 ms) decrease in spiking of all neurons throughout the electrode array. The early response of excitatory but not inhibitory neurons decayed rapidly with distance from the stimulation site over 1 mm. Effective connectivity of neurons with significant stimulus response was dense in wakefulness and sparse under anesthesia. The number of network motifs, especially those of higher order, increased rapidly as the anesthesia was withdrawn indicating a substantial increase in network connectivity as the animals woke up. Conclusion The results illuminate the impact of anesthesia on functional integrity of local cortical circuits affecting the state of consciousness.
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Affiliation(s)
- Anthony G Hudetz
- Department of Anesthesiology, Center for Consciousness Science, University of Michigan, Ann Arbor, MI, United States
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2
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Mashour GA. Anesthesia and the neurobiology of consciousness. Neuron 2024; 112:1553-1567. [PMID: 38579714 PMCID: PMC11098701 DOI: 10.1016/j.neuron.2024.03.002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2024] [Revised: 03/05/2024] [Accepted: 03/06/2024] [Indexed: 04/07/2024]
Abstract
In the 19th century, the discovery of general anesthesia revolutionized medical care. In the 21st century, anesthetics have become indispensable tools to study consciousness. Here, I review key aspects of the relationship between anesthesia and the neurobiology of consciousness, including interfaces of sleep and anesthetic mechanisms, anesthesia and primary sensory processing, the effects of anesthetics on large-scale functional brain networks, and mechanisms of arousal from anesthesia. I discuss the implications of the data derived from the anesthetized state for the science of consciousness and then conclude with outstanding questions, reflections, and future directions.
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Affiliation(s)
- George A Mashour
- Center for Consciousness Science, Department of Anesthesiology, Department of Pharmacology, Neuroscience Graduate Program, University of Michigan Medical School, Ann Arbor, MI 48109, USA.
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Hudetz AG. Microstimulation reveals anesthetic state-dependent effective connectivity of neurons in cerebral cortex. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.04.29.591664. [PMID: 38746366 PMCID: PMC11092428 DOI: 10.1101/2024.04.29.591664] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/16/2024]
Abstract
Complex neuronal interactions underlie cortical information processing that can be compromised in altered states of consciousness. Here intracortical microstimulation was applied to investigate the state-dependent effective connectivity of neurons in rat visual cortex in vivo. Extracellular activity was recorded at 32 sites in layers 5/6 while stimulating with charge-balanced discrete pulses at each electrode in random order. The same stimulation pattern was applied at three levels of anesthesia with desflurane and in wakefulness. Spikes were sorted and classified by their waveform features as putative excitatory and inhibitory neurons. Microstimulation caused early (<10ms) increase followed by prolonged (11-100ms) decrease in spiking of all neurons throughout the electrode array. The early response of excitatory but not inhibitory neurons decayed rapidly with distance from the stimulation site over 1mm. Effective connectivity of neurons with significant stimulus response was dense in wakefulness and sparse under anesthesia. Network motifs were identified in graphs of effective connectivity constructed from monosynaptic cross-correlograms. The number of motifs, especially those of higher order, increased rapidly as the anesthesia was withdrawn indicating a substantial increase in network connectivity as the animals woke up. The results illuminate the impact of anesthesia on functional integrity of local circuits affecting the state of consciousness.
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Tanabe S, Lee H, Wang S, Hudetz AG. Spontaneous and Visual Stimulation Evoked Firing Sequences Are Distinct Under Desflurane Anesthesia. Neuroscience 2023; 528:54-63. [PMID: 37473851 DOI: 10.1016/j.neuroscience.2023.07.016] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2023] [Revised: 07/09/2023] [Accepted: 07/12/2023] [Indexed: 07/22/2023]
Abstract
Recurring spike sequences are thought to underlie cortical computations and may be essential for information processing in the conscious state. How anesthesia at graded levels may influence spontaneous and stimulus-related spike sequences in visual cortex has not been fully elucidated. We recorded extracellular single-unit activity in the rat primary visual cortex in vivo during wakefulness and three levels of anesthesia produced by desflurane. The latencies of spike sequences within 0-200 ms from the onset of spontaneous UP states and visual flash-evoked responses were compared. During wakefulness, spike latency patterns linked to the local field potential theta cycle were similar to stimulus-evoked patterns. Under desflurane anesthesia, spontaneous UP state sequences differed from flash-evoked sequences due to the recruitment of low-firing excitatory neurons to the UP state. Flash-evoked spike sequences showed higher reliability and longer latency when stimuli were applied during DOWN states compared to UP states. At deeper levels, desflurane altered both UP state and flash-evoked spike sequences by selectively suppressing inhibitory neuron firing. The results reveal desflurane-induced complex changes in cortical firing sequences that may influence visual information processing.
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Affiliation(s)
- Sean Tanabe
- Center for Consciousness Science, Department of Anesthesiology, University of Michigan, Ann Arbor, MI 48105, USA
| | - Heonsoo Lee
- Center for Consciousness Science, Department of Anesthesiology, University of Michigan, Ann Arbor, MI 48105, USA
| | - Shiyong Wang
- Center for Consciousness Science, Department of Anesthesiology, University of Michigan, Ann Arbor, MI 48105, USA
| | - Anthony G Hudetz
- Center for Consciousness Science, Department of Anesthesiology, University of Michigan, Ann Arbor, MI 48105, USA.
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Doubovikov ED, Serdyukova NA, Greenberg SB, Gascoigne DA, Minhaj MM, Aksenov DP. Electric Field Effects on Brain Activity: Implications for Epilepsy and Burst Suppression. Cells 2023; 12:2229. [PMID: 37759452 PMCID: PMC10527339 DOI: 10.3390/cells12182229] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2023] [Revised: 08/07/2023] [Accepted: 09/04/2023] [Indexed: 09/29/2023] Open
Abstract
Electric fields are now considered a major mechanism of epileptiform activity. However, it is not clear if another electrophysiological phenomenon, burst suppression, utilizes the same mechanism for its bursting phase. Thus, the purpose of this study was to compare the role of ephaptic coupling-the recruitment of neighboring cells via electric fields-in generating bursts in epilepsy and burst suppression. We used local injections of the GABA-antagonist picrotoxin to elicit epileptic activity and a general anesthetic, sevoflurane, to elicit burst suppression in rabbits. Then, we applied an established computational model of pyramidal cells to simulate neuronal activity in a 3-dimensional grid, with an additional parameter to trigger a suppression phase based on extra-cellular calcium dynamics. We discovered that coupling via electric fields was sufficient to produce bursting in scenarios where inhibitory control of excitatory neurons was sufficiently low. Under anesthesia conditions, bursting occurs with lower neuronal recruitment in comparison to seizures. Our model predicts that due to the effect of electric fields, the magnitude of bursts during seizures should be roughly 2-3 times the magnitude of bursts that occur during burst suppression, which is consistent with our in vivo experimental results. The resulting difference in magnitude between bursts during anesthesia and epileptiform bursts reflects the strength of the electric field effect, which suggests that burst suppression and epilepsy share the same ephaptic coupling mechanism.
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Affiliation(s)
- Evan D. Doubovikov
- Department of Radiology, NorthShore University HealthSystem, Evanston, IL 60201, USA
| | - Natalya A. Serdyukova
- Department of Biomedical Engineering, Northwestern University, Evanston, IL 60208, USA
- Department of Pediatrics, NorthShore University HealthSystem, Evanston, IL 60201, USA
| | - Steven B. Greenberg
- Department of Anesthesiology, NorthShore University HealthSystem, Evanston, IL 60201, USA
| | - David A. Gascoigne
- Department of Radiology, NorthShore University HealthSystem, Evanston, IL 60201, USA
| | - Mohammed M. Minhaj
- Department of Anesthesiology, NorthShore University HealthSystem, Evanston, IL 60201, USA
| | - Daniil P. Aksenov
- Department of Radiology, NorthShore University HealthSystem, Evanston, IL 60201, USA
- Department of Biomedical Engineering, Northwestern University, Evanston, IL 60208, USA
- Department of Anesthesiology, NorthShore University HealthSystem, Evanston, IL 60201, USA
- Pritzker School of Medicine, University of Chicago, Chicago, IL 60637, USA
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Margalit SN, Golomb NG, Tsur O, Ben Yehoshua E, Raz A, Slovin H. Spatiotemporal patterns of population response in the visual cortex under isoflurane: from wakefulness to loss of consciousness. Cereb Cortex 2022; 32:5512-5529. [PMID: 35169840 DOI: 10.1093/cercor/bhac031] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2021] [Revised: 12/22/2021] [Accepted: 01/18/2022] [Indexed: 01/25/2023] Open
Abstract
Anesthetic drugs are widely used in medicine and research to mediate loss of consciousness (LOC). Isoflurane is a commonly used anesthetic drug; however, its effects on cortical sensory processing, in particular around LOC, are not well understood. Using voltage-sensitive dye imaging, we measured visually evoked neuronal population response from the visual cortex in awake and anesthetized mice at 3 increasing concentrations of isoflurane, thus controlling the level of anesthesia from wakefulness to deep anesthesia. At low concentration of isoflurane, the effects on neuronal measures were minor relative to the awake condition. These effects augmented with increasing isoflurane concentration, while around LOC point, they showed abrupt and nonlinear changes. At the network level, we found that isoflurane decreased the stimulus-evoked intra-areal spatial spread of local neural activation, previously reported to be mediated by horizontal connections, and also reduced intra-areal synchronization of neuronal population. The synchronization between different visual areas decreased with higher isoflurane levels. Isoflurane reduced the population response amplitude and prolonged their latencies while higher visual areas showed increased vulnerability to isoflurane concentration. Our results uncover the changes in neural activity and synchronization at isoflurane concentrations leading to LOC and suggest reverse hierarchical shutdown of cortical areas.
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Affiliation(s)
- Shany Nivinsky Margalit
- The Gonda Multidisciplinary Brain Research Center, Bar-Ilan University, Ramat Gan 5290002, Israel
| | - Neta Gery Golomb
- Department of Anesthesiology, Rambam Health Care Campus, Haifa, 3109601, Israel and The Ruth and Bruce Rappaport Faculty of Medicine, Technion - Israel Institute of Technology, Haifa 3200003, Israel
| | - Omer Tsur
- The Gonda Multidisciplinary Brain Research Center, Bar-Ilan University, Ramat Gan 5290002, Israel
| | - Eve Ben Yehoshua
- The Gonda Multidisciplinary Brain Research Center, Bar-Ilan University, Ramat Gan 5290002, Israel
| | - Aeyal Raz
- Department of Anesthesiology, Rambam Health Care Campus, Haifa, 3109601, Israel and The Ruth and Bruce Rappaport Faculty of Medicine, Technion - Israel Institute of Technology, Haifa 3200003, Israel
| | - Hamutal Slovin
- The Gonda Multidisciplinary Brain Research Center, Bar-Ilan University, Ramat Gan 5290002, Israel
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Bharioke A, Munz M, Brignall A, Kosche G, Eizinger MF, Ledergerber N, Hillier D, Gross-Scherf B, Conzelmann KK, Macé E, Roska B. General anesthesia globally synchronizes activity selectively in layer 5 cortical pyramidal neurons. Neuron 2022; 110:2024-2040.e10. [PMID: 35452606 PMCID: PMC9235854 DOI: 10.1016/j.neuron.2022.03.032] [Citation(s) in RCA: 44] [Impact Index Per Article: 22.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2020] [Revised: 10/30/2021] [Accepted: 03/28/2022] [Indexed: 12/27/2022]
Abstract
General anesthetics induce loss of consciousness, a global change in behavior. However, a corresponding global change in activity in the context of defined cortical cell types has not been identified. Here, we show that spontaneous activity of mouse layer 5 pyramidal neurons, but of no other cortical cell type, becomes consistently synchronized in vivo by different general anesthetics. This heightened neuronal synchrony is aperiodic, present across large distances, and absent in cortical neurons presynaptic to layer 5 pyramidal neurons. During the transition to and from anesthesia, changes in synchrony in layer 5 coincide with the loss and recovery of consciousness. Activity within both apical and basal dendrites is synchronous, but only basal dendrites’ activity is temporally locked to somatic activity. Given that layer 5 is a major cortical output, our results suggest that brain-wide synchrony in layer 5 pyramidal neurons may contribute to the loss of consciousness during general anesthesia. Activity of layer 5 PNs synchronizes globally in different anesthetics Other mouse cortical cell types show no consistent increase in synchrony Changes in layer 5 synchrony coincide with the loss and recovery of consciousness Basal, but not apical, layer 5 dendrites are in synchrony with somas
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Affiliation(s)
- Arjun Bharioke
- Institute of Molecular and Clinical Ophthalmology Basel, Basel, Switzerland; Department of Ophthalmology, University of Basel, Basel, Switzerland; Friedrich Miescher Institute for Biomedical Research, Basel, Switzerland
| | - Martin Munz
- Institute of Molecular and Clinical Ophthalmology Basel, Basel, Switzerland; Department of Ophthalmology, University of Basel, Basel, Switzerland; Friedrich Miescher Institute for Biomedical Research, Basel, Switzerland
| | - Alexandra Brignall
- Institute of Molecular and Clinical Ophthalmology Basel, Basel, Switzerland; Department of Ophthalmology, University of Basel, Basel, Switzerland
| | - Georg Kosche
- Institute of Molecular and Clinical Ophthalmology Basel, Basel, Switzerland; Department of Ophthalmology, University of Basel, Basel, Switzerland; Friedrich Miescher Institute for Biomedical Research, Basel, Switzerland
| | - Max Ferdinand Eizinger
- Max von Pettenkofer-Institute, Virology, Medical Faculty and Gene Center, Ludwig Maximilians University, Munich, Germany
| | - Nicole Ledergerber
- Institute of Molecular and Clinical Ophthalmology Basel, Basel, Switzerland; Department of Ophthalmology, University of Basel, Basel, Switzerland; Friedrich Miescher Institute for Biomedical Research, Basel, Switzerland
| | - Daniel Hillier
- Institute of Molecular and Clinical Ophthalmology Basel, Basel, Switzerland; Department of Ophthalmology, University of Basel, Basel, Switzerland; Friedrich Miescher Institute for Biomedical Research, Basel, Switzerland; Institute of Cognitive Neuroscience and Psychology, Research Centre for Natural Sciences, Budapest, Hungary
| | - Brigitte Gross-Scherf
- Institute of Molecular and Clinical Ophthalmology Basel, Basel, Switzerland; Department of Ophthalmology, University of Basel, Basel, Switzerland; Friedrich Miescher Institute for Biomedical Research, Basel, Switzerland
| | - Karl-Klaus Conzelmann
- Max von Pettenkofer-Institute, Virology, Medical Faculty and Gene Center, Ludwig Maximilians University, Munich, Germany
| | - Emilie Macé
- Brain-Wide Circuits for Behavior Research Group, Max Planck Institute of Neurobiology, Martinsried, Germany
| | - Botond Roska
- Institute of Molecular and Clinical Ophthalmology Basel, Basel, Switzerland; Department of Ophthalmology, University of Basel, Basel, Switzerland; Friedrich Miescher Institute for Biomedical Research, Basel, Switzerland.
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8
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Liang T, Wu F, Sun Y, Wang B. Electrophysiological Activity and Brain Network During Recovery of Propofol Anesthesia: A Stereoelectroencephalography-Based Analysis in Patients With Intractable Epilepsy—An Exploratory Research. Front Neurol 2021. [DOI: 10.3389/fneur.2021.694964] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Background: The oscillations and interactions between different brain areas during recovery of consciousness (ROC) from anesthesia in humans are poorly understood. Reliable stereoelectroencephalography (SEEG) signatures for transitions between unconsciousness and consciousness under anesthesia have not yet been fully identified.Objective: This study was designed to observe the change of electrophysiological activity during ROC and construct a ROC network based on SEEG data to describe the network property of cortical and deep areas during ROC from propofol-induced anesthetic epileptic patients.Methods: We analyzed SEEG data recorded from sixteen right-handed epileptic patients during ROC from propofol anesthesia from March 1, 2019, to December 31, 2019. Power spectrum density (PSD), correlation, and coherence were used to describe different brain areas' electrophysiological activity. The clustering coefficient, characteristic path length, modularity, network efficiency, degrees, and betweenness centrality were used to describe the network changes during ROC from propofol anesthesia. Statistical analysis was performed using MATLAB 2016b. The power spectral data from different contacts were analyzed using a one-way analysis of variance (ANOVA) test with Tukey's post-hoc correction. One sample t-test was used for the analysis of network property. Kolmogorov-Smirnov test was used to judge data distribution. Non-normal distribution was analyzed using the signed rank-sum test.Result: From the data of these 16 patients, 10 cortical, and 22 deep positions were observed. In this network, we observed that bilateral occipital areas are essential parts that have strong links with many regions. The recovery process is different in the bilateral cerebral cortex. Stage B (propofol 3.0-2.5 μg/ml) and E (propofol 1.5 μg/ml-ROC) play important roles during ROC exhibiting significant changes. The clustering coefficient gradually decreases with the recovery from anesthesia, and the changes mainly come from the cortical region. The characteristic path length and network efficiency do not change significantly during the recovery from anesthesia, and the changes of network modularity and clustering coefficient are similar. Deep areas tend to form functional modules. The left occipital lobe, the left temporal lobe, bilateral amygdala are essential nodes in the network. Some specific cortical regions (i.e., left angular gyrus, right angular gyrus, right temporal lobe, left temporal lobe, and right angular gyrus) and deep regions (i.e., right amygdala, left cingulate gyrus, right insular lobe, right amygdala) have more significant constraints on other regions.Conclusion: We verified that the bilateral cortex's recovery process is the opposite, which is not found in the deep regions. Significant PSD changes were observed in many areas at the beginning of stop infusion and near recovery. Our study found that during the ROC process, the modularity and clustering coefficient of the deep area network is significantly improved. However, the changes of the bilateral cerebral cortex were different. Power spectrum analysis shows that low-frequency EEG in anesthesia recovery accounts for a large proportion. The changes of the bilateral brain in the process of anesthesia recovery are different. The clustering coefficient gradually decreased with the recovery from anesthesia, and the changes mainly came from the cortical region. The characteristic path length and network efficiency do not change significantly during the recovery from anesthesia, and the changes of network modularity and clustering coefficient were similar. During ROC, the left occipital lobe, the left temporal lobe, bilateral amygdala were essential nodes in the network. The findings of the current study suggest SEEG as an effective tool for providing direct evidence of the anesthesia recovery mechanism.
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Sparse Coding in Temporal Association Cortex Improves Complex Sound Discriminability. J Neurosci 2021; 41:7048-7064. [PMID: 34244361 DOI: 10.1523/jneurosci.3167-20.2021] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2020] [Revised: 06/05/2021] [Accepted: 06/18/2021] [Indexed: 11/21/2022] Open
Abstract
The mouse auditory cortex is comprised of several auditory fields spanning the dorsoventral axis of the temporal lobe. The ventral most auditory field is the temporal association cortex (TeA), which remains largely unstudied. Using Neuropixels probes, we simultaneously recorded from primary auditory cortex (AUDp), secondary auditory cortex (AUDv), and TeA, characterizing neuronal responses to pure tones and frequency modulated (FM) sweeps in awake head-restrained female mice. As compared with AUDp and AUDv, single-unit (SU) responses to pure tones in TeA were sparser, delayed, and prolonged. Responses to FMs were also sparser. Population analysis showed that the sparser responses in TeA render it less sensitive to pure tones, yet more sensitive to FMs. When characterizing responses to pure tones under anesthesia, the distinct signature of TeA was changed considerably as compared with that in awake mice, implying that responses in TeA are strongly modulated by non-feedforward connections. Together, these findings provide a basic electrophysiological description of TeA as an integral part of sound processing along the cortical hierarchy.SIGNIFICANCE STATEMENT This is the first comprehensive characterization of the auditory responses in the awake mouse auditory temporal association cortex (TeA). The study provides the foundations for further investigation of TeA and its involvement in auditory learning, plasticity, auditory driven behaviors etc. The study was conducted using state of the art data collection tools, allowing for simultaneous recording from multiple cortical regions and numerous neurons.
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Schwerin S, Kopp C, Pircher E, Schneider G, Kreuzer M, Haseneder R, Kratzer S. Attenuation of Native Hyperpolarization-Activated, Cyclic Nucleotide-Gated Channel Function by the Volatile Anesthetic Sevoflurane in Mouse Thalamocortical Relay Neurons. Front Cell Neurosci 2021; 14:606687. [PMID: 33551750 PMCID: PMC7858256 DOI: 10.3389/fncel.2020.606687] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2020] [Accepted: 12/18/2020] [Indexed: 11/24/2022] Open
Abstract
As thalamocortical relay neurons are ascribed a crucial role in signal propagation and information processing, they have attracted considerable attention as potential targets for anesthetic modulation. In this study, we analyzed the effects of different concentrations of sevoflurane on the excitability of thalamocortical relay neurons and hyperpolarization-activated, cyclic-nucleotide gated (HCN) channels, which play a decisive role in regulating membrane properties and rhythmic oscillatory activity. The effects of sevoflurane on single-cell excitability and native HCN channels were investigated in acutely prepared brain slices from adult wild-type mice with the whole-cell patch-clamp technique, using voltage-clamp and current-clamp protocols. Sevoflurane dose-dependently depressed membrane biophysics and HCN-mediated parameters of neuronal excitability. Respective half-maximal inhibitory and effective concentrations ranged between 0.30 (95% CI, 0.18–0.50) mM and 0.88 (95% CI, 0.40–2.20) mM. We witnessed a pronounced reduction of HCN dependent Ih current amplitude starting at a concentration of 0.45 mM [relative change at −133 mV; 0.45 mM sevoflurane: 0.85 (interquartile range, 0.79–0.92), n = 12, p = 0.011; 1.47 mM sevoflurane: 0.37 (interquartile range, 0.34–0.62), n = 5, p < 0.001] with a half-maximal inhibitory concentration of 0.88 (95% CI, 0.40–2.20) mM. In contrast, effects on voltage-dependent channel gating were modest with significant changes only occurring at 1.47 mM [absolute change of half-maximal activation potential; 1.47 mM: −7.2 (interquartile range, −10.3 to −5.8) mV, n = 5, p = 0.020]. In this study, we demonstrate that sevoflurane inhibits the excitability of thalamocortical relay neurons in a concentration-dependent manner within a clinically relevant range. Especially concerning its effects on native HCN channel function, our findings indicate substance-specific differences in comparison to other anesthetic agents. Considering the importance of HCN channels, the observed effects might mechanistically contribute to the hypnotic properties of sevoflurane.
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Affiliation(s)
- Stefan Schwerin
- Department of Anesthesiology and Intensive Care Medicine, Technical University of Munich School of Medicine, Munich, Germany
| | - Claudia Kopp
- Department of Anesthesiology and Intensive Care Medicine, Technical University of Munich School of Medicine, Munich, Germany
| | - Elisabeth Pircher
- Department of Anesthesiology and Intensive Care Medicine, Technical University of Munich School of Medicine, Munich, Germany
| | - Gerhard Schneider
- Department of Anesthesiology and Intensive Care Medicine, Technical University of Munich School of Medicine, Munich, Germany
| | - Matthias Kreuzer
- Department of Anesthesiology and Intensive Care Medicine, Technical University of Munich School of Medicine, Munich, Germany
| | - Rainer Haseneder
- Department of Anesthesiology and Intensive Care Medicine, Technical University of Munich School of Medicine, Munich, Germany
| | - Stephan Kratzer
- Department of Anesthesiology and Intensive Care Medicine, Technical University of Munich School of Medicine, Munich, Germany
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11
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Lee H, Tanabe S, Wang S, Hudetz AG. Differential Effect of Anesthesia on Visual Cortex Neurons with Diverse Population Coupling. Neuroscience 2020; 458:108-119. [PMID: 33309966 DOI: 10.1016/j.neuroscience.2020.11.043] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2020] [Revised: 11/16/2020] [Accepted: 11/30/2020] [Indexed: 12/15/2022]
Abstract
Cortical neurons display diverse firing patterns and synchronization properties. How anesthesia alters the firing response of different neuron groups relevant for sensory information processing is unclear. Here we investigated the graded effect of anesthesia on spontaneous and visual flash-induced spike activity of different neuron groups classified based on their spike waveform, firing rate, and population coupling (the extent neurons conform to population spikes). Single-unit activity was measured from multichannel extracellular recordings in deep layers of primary visual cortex of freely moving rats in wakefulness and at three concentrations of desflurane. Anesthesia generally decreased firing rate and increased population coupling and burstiness of neurons. Population coupling and firing rate became more correlated and the pairwise correlation between neurons became more predictable by their population coupling in anesthesia. During wakefulness, visual stimulation increased firing rate; this effect was the largest and the most prolonged in neurons that exhibited high population coupling and high firing rate. During anesthesia, the early increase in firing rate (20-150 ms post-stimulus) of these neurons was suppressed, their spike timing was delayed and split into two peaks. The late response (200-400 ms post-stimulus) of all neurons was also suppressed. We conclude that anesthesia alters the visual response of primarily high-firing highly coupled neurons, which may interfere with visual sensory processing. The increased association of population coupling and firing rate during anesthesia suggests a decrease in sensory information content.
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Affiliation(s)
- Heonsoo Lee
- Center for Consciousness Science, Department of Anesthesiology, University of Michigan, Ann Arbor, MI 48109, USA
| | - Sean Tanabe
- Center for Consciousness Science, Department of Anesthesiology, University of Michigan, Ann Arbor, MI 48109, USA
| | - Shiyong Wang
- Center for Consciousness Science, Department of Anesthesiology, University of Michigan, Ann Arbor, MI 48109, USA
| | - Anthony G Hudetz
- Center for Consciousness Science, Department of Anesthesiology, University of Michigan, Ann Arbor, MI 48109, USA.
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12
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Perenboom MJL, Schenke M, Ferrari MD, Terwindt GM, van den Maagdenberg AMJM, Tolner EA. Responsivity to light in familial hemiplegic migraine type 1 mutant mice reveals frequency-dependent enhancement of visual network excitability. Eur J Neurosci 2020; 53:1672-1686. [PMID: 33170971 PMCID: PMC8048865 DOI: 10.1111/ejn.15041] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2020] [Revised: 10/13/2020] [Accepted: 11/01/2020] [Indexed: 12/01/2022]
Abstract
Migraine patients often report (inter)ictal hypersensitivity to light, but the underlying mechanisms remain an enigma. Both hypo- and hyperresponsivity of the visual network have been reported, which may reflect either intra-individual dynamics of the network or large inter-individual variation in the measurement of human visual evoked potential data. Therefore, we studied visual system responsivity in freely behaving mice using combined epidural electroencephalography and intracortical multi-unit activity to reduce variation in recordings and gain insight into visual cortex dynamics. For better clinical translation, we investigated transgenic mice that carry the human pathogenic R192Q missense mutation in the α1A subunit of voltage-gated CaV 2.1 Ca2+ channels leading to enhanced neurotransmission and familial hemiplegic migraine type 1 in patients. Visual evoked potentials were studied in response to visual stimulation paradigms with flashes of light. Following intensity-dependent visual stimulation, FHM1 mutant mice displayed faster visual evoked potential responses, with lower initial amplitude, followed by less pronounced neuronal suppression compared to wild-type mice. Similar to what was reported for migraine patients, frequency-dependent stimulation in mutant mice revealed enhanced photic drive in the EEG beta-gamma band. The frequency-dependent increases in visual network responses in mutant mice may reflect the context-dependent enhancement of visual cortex excitability, which could contribute to our understanding of sensory hypersensitivity in migraine.
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Affiliation(s)
| | - Maarten Schenke
- Department of Neurology, Leiden University Medical Center, Leiden, The Netherlands.,Department of Human Genetics, Leiden University Medical Center, Leiden, The Netherlands
| | - Michel D Ferrari
- Department of Neurology, Leiden University Medical Center, Leiden, The Netherlands
| | - Gisela M Terwindt
- Department of Neurology, Leiden University Medical Center, Leiden, The Netherlands
| | - Arn M J M van den Maagdenberg
- Department of Neurology, Leiden University Medical Center, Leiden, The Netherlands.,Department of Human Genetics, Leiden University Medical Center, Leiden, The Netherlands
| | - Else A Tolner
- Department of Neurology, Leiden University Medical Center, Leiden, The Netherlands.,Department of Human Genetics, Leiden University Medical Center, Leiden, The Netherlands
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13
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Mashour GA, Roelfsema P, Changeux JP, Dehaene S. Conscious Processing and the Global Neuronal Workspace Hypothesis. Neuron 2020; 105:776-798. [PMID: 32135090 PMCID: PMC8770991 DOI: 10.1016/j.neuron.2020.01.026] [Citation(s) in RCA: 382] [Impact Index Per Article: 95.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2019] [Revised: 10/31/2019] [Accepted: 01/22/2020] [Indexed: 10/24/2022]
Abstract
We review the central tenets and neuroanatomical basis of the global neuronal workspace (GNW) hypothesis, which attempts to account for the main scientific observations regarding the elementary mechanisms of conscious processing in the human brain. The GNW hypothesis proposes that, in the conscious state, a non-linear network ignition associated with recurrent processing amplifies and sustains a neural representation, allowing the corresponding information to be globally accessed by local processors. We examine this hypothesis in light of recent data that contrast brain activity evoked by either conscious or non-conscious contents, as well as during conscious or non-conscious states, particularly general anesthesia. We also discuss the relationship between the intertwined concepts of conscious processing, attention, and working memory.
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Affiliation(s)
- George A Mashour
- Center for Consciousness Science, Neuroscience Graduate Program, and Department of Anesthesiology, University of Michigan, Ann Arbor, MI, USA
| | - Pieter Roelfsema
- Department of Vision & Cognition, Netherlands Institute for Neuroscience, Meibergdreef 47, 1105 BA, Amsterdam, the Netherlands; Department of Integrative Neurophysiology, Center for Neurogenomics and Cognitive Research, VU University, Amsterdam, the Netherlands; Department of Psychiatry, Academic Medical Center, Amsterdam, the Netherlands
| | - Jean-Pierre Changeux
- CNRS UMR 3571, Institut Pasteur, 75724 Paris, France; Collège de France, 11 Place Marcelin Berthelot, 75005 Paris, France; Kavli Institute for Brain & Mind, University of California, San Diego, La Jolla, CA, USA.
| | - Stanislas Dehaene
- Collège de France, 11 Place Marcelin Berthelot, 75005 Paris, France; Cognitive Neuroimaging Unit, CEA, INSERM, Université Paris-Sud, Université Paris-Saclay, NeuroSpin Center, 91191 Gif/Yvette, France.
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14
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Abstract
The science of transitional states of consciousness is reviewed. Despite intensive study, determining the subjective experience of animals during transitional states of consciousness remains inherently limited. Until better assessment tools become available, behavior-based observations, such as loss of righting reflex/loss of posture, remain among our most useful guides to the onset of unconsciousness in animals. To minimize potential animal suffering and to ensure a truly unconscious state is unambiguously achieved, a state of general anesthesia relying on gamma amino butyric acid type A agonists or N-methyl-d-aspartate antagonist agents continues to be a necessary component of the companion animal euthanasia process.
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Affiliation(s)
- Robert E Meyer
- Veterinary Anesthesiology, College of Veterinary Medicine, PO Box 6100, Campus Mailstop 9825, 240 Wise Center Drive, Mississippi State, MS 39762-6100, USA.
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15
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Murphy C, Krause B, Banks M. Selective effects of isoflurane on cortico-cortical feedback afferent responses in murine non-primary neocortex. Br J Anaesth 2019; 123:488-496. [PMID: 31383363 DOI: 10.1016/j.bja.2019.06.018] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2019] [Revised: 05/28/2019] [Accepted: 06/22/2019] [Indexed: 02/07/2023] Open
Abstract
BACKGROUND General anaesthetics affect loss of consciousness by disrupting information-passing and integration within thalamo-cortical (TC) networks. Feedback cortical connections that carry internally generated signals such as expectation and attention appear more sensitive to anaesthesia than feedforward signals. However, direct evidence for this effect in non-primary cortex is lacking. In addition, direct comparisons between TC core and matrix, and between cortico-cortical (CC) feedforward and feedback responses have not been reported. METHODS We investigated the disruption of synaptic responses by isoflurane of four distinct afferent pathways to non-primary neocortex. We independently activated TC core and matrix and reciprocal CC (feedforward and feedback) pathways using optogenetic techniques, and compared the relative sensitivity of synaptic responses to isoflurane. RESULTS Under control conditions, activation of axon terminals of all pathways evoked postsynaptic currents (recorded extracellularly) and postsynaptic potentials in pyramidal neurones. CC feedback responses were substantially more sensitive to isoflurane (0 to 0.53 mM) compared with TC core, TC matrix, or CC feedforward pathways. CONCLUSION Differential sensitivity of CC feedback synaptic responses to isoflurane in a clinically relevant range suggests a role for disruption of these afferents in the hypnotic effects of anaesthetic agents.
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Affiliation(s)
- Caitlin Murphy
- Physiology Graduate Training Program, University of Wisconsin School of Medicine and Public Health, Madison, WI, USA; Department of Anesthesiology, University of Wisconsin School of Medicine and Public Health, Madison, WI, USA.
| | - Bryan Krause
- Department of Anesthesiology, University of Wisconsin School of Medicine and Public Health, Madison, WI, USA
| | - Matthew Banks
- Department of Anesthesiology, University of Wisconsin School of Medicine and Public Health, Madison, WI, USA
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16
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Hentschke H, Raz A, Krause BM, Murphy CA, Banks MI. Disruption of cortical network activity by the general anaesthetic isoflurane. Br J Anaesth 2019; 119:685-696. [PMID: 29121295 DOI: 10.1093/bja/aex199] [Citation(s) in RCA: 25] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/02/2017] [Indexed: 02/03/2023] Open
Abstract
Background Actions of general anaesthetics on activity in the cortico-thalamic network likely contribute to loss of consciousness and disconnection from the environment. Previously, we showed that the general anaesthetic isoflurane preferentially suppresses cortically evoked synaptic responses compared with thalamically evoked synaptic responses, but how this differential sensitivity translates into changes in network activity is unclear. Methods We investigated isoflurane disruption of spontaneous and stimulus-induced cortical network activity using multichannel recordings in murine auditory thalamo-cortical brain slices. Results Under control conditions, afferent stimulation elicited short latency, presumably monosynaptically driven, spiking responses, as well as long latency network bursts that propagated horizontally through the cortex. Isoflurane (0.05-0.6 mM) suppressed spiking activity overall, but had a far greater effect on network bursts than on early spiking responses. At isoflurane concentrations >0.3 mM, network bursts were almost entirely blocked, even with increased stimulation intensity and in response to paired (thalamo-cortical + cortical layer 1) stimulation, while early spiking responses were <50% blocked. Isoflurane increased the threshold for eliciting bursts, decreased their propagation speed and prevented layer 1 afferents from facilitating burst induction by thalamo-cortical afferents. Conclusions Disruption of horizontal activity spread and of layer 1 facilitation of thalamo-cortical responses likely contribute to the mechanism by which suppression of cortical feedback connections disrupts sensory awareness under anaesthesia.
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Affiliation(s)
- H Hentschke
- Department of Anesthesiology, Experimental Anesthesiology Section, University Hospital of Tübingen, Tübingen, Germany
| | - A Raz
- Department of Anesthesiology, University of Wisconsin, Madison, WI, USA.,Department of Anesthesiology, Rambam Health Care Campus, Haifa, Israel
| | - B M Krause
- Department of Anesthesiology, University of Wisconsin, Madison, WI, USA
| | - C A Murphy
- Department of Anesthesiology, University of Wisconsin, Madison, WI, USA.,Physiology Graduate Training Program, University of Wisconsin, Madison, WI, USA
| | - M I Banks
- Department of Anesthesiology, University of Wisconsin, Madison, WI, USA
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17
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Palanca BJA, Avidan MS, Mashour GA. Human neural correlates of sevoflurane-induced unconsciousness. Br J Anaesth 2019; 119:573-582. [PMID: 29121298 DOI: 10.1093/bja/aex244] [Citation(s) in RCA: 55] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/11/2017] [Indexed: 01/01/2023] Open
Abstract
Sevoflurane, a volatile anaesthetic agent well-tolerated for inhalation induction, provides a useful opportunity to elucidate the processes whereby halogenated ethers disrupt consciousness and cognition. Multiple molecular targets of sevoflurane have been identified, complementing imaging and electrophysiologic markers for the mechanistically obscure progression from wakefulness to unconsciousness. Recent investigations have more precisely detailed scalp EEG activity during this transition, with practical clinical implications. The relative timing of scalp potentials in frontal and parietal EEG signals suggests that sevoflurane might perturb the propagation of neural information between underlying cortical regions. Spatially distributed brain activity during general anaesthesia has been further investigated with positron emission tomography (PET) and resting-state functional magnetic resonance imaging (fMRI). Combined EEG and PET investigations have identified changes in cerebral blood flow and metabolic activity in frontal, parietal, and thalamic regions during sevoflurane-induced loss of consciousness. More recent fMRI investigations have revealed that sevoflurane weakens the signal correlations among brain regions that share functionality and specialization during wakefulness. In particular, two such resting-state networks have shown progressive breakdown in intracortical and thalamocortical connectivity with increasing anaesthetic concentrations: the Default Mode Network (introspection and episodic memory) and the Ventral Attention Network (orienting of attention to salient feature of the external world). These data support the hypotheses that perturbations in temporally correlated activity across brain regions contribute to the transition between states of sevoflurane sedation and general anaesthesia.
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Affiliation(s)
- B J A Palanca
- Division of Biology and Biomedical Sciences.,Department of Anesthesiology, Washington University School of Medicine in St. Louis, St. Louis, MO, USA
| | - M S Avidan
- Department of Anesthesiology, Washington University School of Medicine in St. Louis, St. Louis, MO, USA.,Division of Cardiothoracic Surgery, Department of Surgery, Washington University School of Medicine in St. Louis, St. Louis, MO, USA
| | - G A Mashour
- Department of Anesthesiology, Center for Consciousness Science and Neuroscience Graduate Program, University of Michigan Medical School, Ann Arbor, MI, USA
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18
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Abstract
The heterogeneity of molecular mechanisms, target neural circuits, and neurophysiologic effects of general anesthetics makes it difficult to develop a reliable and drug-invariant index of general anesthesia. No single brain region or mechanism has been identified as the neural correlate of consciousness, suggesting that consciousness might emerge through complex interactions of spatially and temporally distributed brain functions. The goal of this review article is to introduce the basic concepts of networks and explain why the application of network science to general anesthesia could be a pathway to discover a fundamental mechanism of anesthetic-induced unconsciousness. This article reviews data suggesting that reduced network efficiency, constrained network repertoires, and changes in cortical dynamics create inhospitable conditions for information processing and transfer, which lead to unconsciousness. This review proposes that network science is not just a useful tool but a necessary theoretical framework and method to uncover common principles of anesthetic-induced unconsciousness.
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Affiliation(s)
- UnCheol Lee
- From the Center for Consciousness Science, Department of Anesthesiology, University of Michigan Medical School, Ann Arbor, Michigan
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19
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Banks MI, Moran NS, Krause BM, Grady SM, Uhlrich DJ, Manning KA. Altered stimulus representation in rat auditory cortex is not causal for loss of consciousness under general anaesthesia. Br J Anaesth 2018; 121:605-615. [PMID: 30115259 DOI: 10.1016/j.bja.2018.05.054] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2018] [Revised: 05/13/2018] [Accepted: 05/21/2018] [Indexed: 02/06/2023] Open
Abstract
BACKGROUND Current concepts suggest that impaired representation of information in cortical networks contributes to loss of consciousness under anaesthesia. We tested this idea in rat auditory cortex using information theory analysis of multiunit responses recorded under three anaesthetic agents with different molecular targets: isoflurane, propofol, and dexmedetomidine. We reasoned that if changes in the representation of sensory stimuli are causal for loss of consciousness, they should occur regardless of the specific anaesthetic agent. METHODS Spiking responses were recorded with chronically implanted microwire arrays in response to acoustic stimuli incorporating varied temporal and spectral dynamics. Experiments consisted of four drug conditions: awake (pre-drug), sedation (i.e. intact righting reflex), loss of consciousness (a dose just sufficient to cause loss of righting reflex), and recovery. Measures of firing rate, spike timing, and mutual information were analysed as a function of drug condition. RESULTS All three drugs decreased spontaneous and evoked spiking activity and modulated spike timing. However, changes in mutual information were inconsistent with altered stimulus representation being causal for loss of consciousness. First, direction of change in mutual information was agent-specific, increasing under dexmedetomidine and decreasing under isoflurane and propofol. Second, mutual information did not decrease at the transition between sedation and LOC for any agent. Changes in mutual information under anaesthesia correlated strongly with changes in precision and reliability of spike timing, consistent with the importance of temporal stimulus features in driving auditory cortical activity. CONCLUSIONS The primary sensory cortex is not the locus for changes in representation of information causal for loss of consciousness under anaesthesia.
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Affiliation(s)
- M I Banks
- Department of Anesthesiology, University of Wisconsin, Madison, WI, USA.
| | - N S Moran
- Neuroscience Training Program, University of Wisconsin, Madison, WI, USA
| | - B M Krause
- Department of Anesthesiology, University of Wisconsin, Madison, WI, USA
| | - S M Grady
- Department of Anesthesiology, University of Wisconsin, Madison, WI, USA
| | - D J Uhlrich
- Department of Neuroscience, University of Wisconsin, Madison, WI, USA
| | - K A Manning
- Department of Neuroscience, University of Wisconsin, Madison, WI, USA
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20
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Mashour GA, Hudetz AG. Fading whispers down the lane: signal propagation in anaesthetized cortical networks. Br J Anaesth 2017; 119:568-570. [PMID: 29121276 DOI: 10.1093/bja/aex215] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Affiliation(s)
- G A Mashour
- Department of Anesthesiology, Center for Consciousness Science, Neuroscience Graduate Program, University of Michigan Medical School, Ann Arbor, MI, USA
| | - A G Hudetz
- Department of Anesthesiology, Center for Consciousness Science, Neuroscience Graduate Program, University of Michigan Medical School, Ann Arbor, MI, USA
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21
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Juxtaposing the real-time unfolding of subjective experience and ERP neuromarker dynamics. Conscious Cogn 2017; 54:3-19. [DOI: 10.1016/j.concog.2017.05.003] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2016] [Revised: 05/10/2017] [Accepted: 05/11/2017] [Indexed: 01/08/2023]
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22
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Wang X, Gkogkidis CA, Iljina O, Fiederer LDJ, Henle C, Mader I, Kaminsky J, Stieglitz T, Gierthmuehlen M, Ball T. Mapping the fine structure of cortical activity with different micro-ECoG electrode array geometries. J Neural Eng 2017; 14:056004. [DOI: 10.1088/1741-2552/aa785e] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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23
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Abstract
A quest for a systems-level neuroscientific basis of anesthetic-induced loss and return of consciousness has been in the forefront of research for the past 2 decades. Recent advances toward the discovery of underlying mechanisms have been achieved using experimental electrophysiology, multichannel electroencephalography, magnetoencephalography, and functional magnetic resonance imaging. By the careful dosing of various volatile and IV anesthetic agents to the level of behavioral unresponsiveness, both specific and common changes in functional and effective connectivity across large-scale brain networks have been discovered and interpreted in the context of how the synthesis of neural information might be affected during anesthesia. The results of most investigations to date converge toward the conclusion that a common neural correlate of anesthetic-induced unresponsiveness is a consistent depression or functional disconnection of lateral frontoparietal networks, which are thought to be critical for consciousness of the environment. A reduction in the repertoire of brain states may contribute to the anesthetic disruption of large-scale information integration leading to unconsciousness. In future investigations, a systematic delineation of connectivity changes with multiple anesthetics using the same experimental design, and the same analytical method will be desirable. The critical neural events that account for the transition between responsive and unresponsive states should be assessed at similar anesthetic doses just below and above the loss or return of responsiveness. There will also be a need to identify a robust, sensitive, and reliable measure of information transfer. Ultimately, finding a behavior-independent measure of subjective experience that can track covert cognition in unresponsive subjects and a delineation of causal factors versus correlated events will be essential to understand the neuronal basis of human consciousness and unconsciousness.
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24
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Uhrig L, Janssen D, Dehaene S, Jarraya B. Cerebral responses to local and global auditory novelty under general anesthesia. Neuroimage 2016; 141:326-340. [PMID: 27502046 PMCID: PMC5635967 DOI: 10.1016/j.neuroimage.2016.08.004] [Citation(s) in RCA: 42] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/01/2016] [Revised: 08/01/2016] [Accepted: 08/03/2016] [Indexed: 12/13/2022] Open
Abstract
Primate brains can detect a variety of unexpected deviations in auditory sequences. The local-global paradigm dissociates two hierarchical levels of auditory predictive coding by examining the brain responses to first-order (local) and second-order (global) sequence violations. Using the macaque model, we previously demonstrated that, in the awake state, local violations cause focal auditory responses while global violations activate a brain circuit comprising prefrontal, parietal and cingulate cortices. Here we used the same local-global auditory paradigm to clarify the encoding of the hierarchical auditory regularities in anesthetized monkeys and compared their brain responses to those obtained in the awake state as measured with fMRI. Both, propofol, a GABAA-agonist, and ketamine, an NMDA-antagonist, left intact or even enhanced the cortical response to auditory inputs. The local effect vanished during propofol anesthesia and shifted spatially during ketamine anesthesia compared with wakefulness. Under increasing levels of propofol, we observed a progressive disorganization of the global effect in prefrontal, parietal and cingulate cortices and its complete suppression under ketamine anesthesia. Anesthesia also suppressed thalamic activations to the global effect. These results suggest that anesthesia preserves initial auditory processing, but disturbs both short-term and long-term auditory predictive coding mechanisms. The disorganization of auditory novelty processing under anesthesia relates to a loss of thalamic responses to novelty and to a disruption of higher-order functional cortical networks in parietal, prefrontal and cingular cortices.
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Affiliation(s)
- Lynn Uhrig
- CEA DRF/I2BM, NeuroSpin Center, 91191 Gif-sur-Yvette, France; INSERM U992, Cognitive Neuroimaging Unit, 91191 Gif-sur-Yvette, France
| | - David Janssen
- CEA DRF/I2BM, NeuroSpin Center, 91191 Gif-sur-Yvette, France
| | - Stanislas Dehaene
- CEA DRF/I2BM, NeuroSpin Center, 91191 Gif-sur-Yvette, France; INSERM U992, Cognitive Neuroimaging Unit, 91191 Gif-sur-Yvette, France; Collège de France, 75231 Paris, France; Université Paris Sud, Université Paris-Saclay, 91405 Orsay, France
| | - Béchir Jarraya
- CEA DRF/I2BM, NeuroSpin Center, 91191 Gif-sur-Yvette, France; INSERM U992, Cognitive Neuroimaging Unit, 91191 Gif-sur-Yvette, France; Neuromodulation Unit, Department of Neurosurgery, Foch Hospital, 92150 Suresnes, France; University of Versailles Saint-Quentin-en-Yvelines, Université Paris-Saclay, 78000 Versailles, France.
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25
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Arena A, Lamanna J, Gemma M, Ripamonti M, Ravasio G, Zimarino V, De Vitis A, Beretta L, Malgaroli A. Linear transformation of the encoding mechanism for light intensity underlies the paradoxical enhancement of cortical visual responses by sevoflurane. J Physiol 2016; 595:321-339. [PMID: 27416731 DOI: 10.1113/jp272215] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2016] [Accepted: 06/30/2016] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS The mechanisms of action of anaesthetics on the living brain are still poorly understood. In this respect, the analysis of the differential effects of anaesthetics on spontaneous and sensory-evoked cortical activity might provide important and novel cues. Here we show that the anaesthetic sevoflurane strongly silences the brain but potentiates in a dose- and frequency-dependent manner the cortical visual response. Such enhancement arises from a linear scaling by sevoflurane of the power-law relation between light intensity and the cortical response. The fingerprint of sevoflurane action suggests that circuit silencing can boost linearly synaptic responsiveness presumably by scaling the number of responding units and/or their correlation following a sensory stimulation. ABSTRACT General anaesthetics, which are expected to silence brain activity, often spare sensory responses. To evaluate differential effects of anaesthetics on spontaneous and sensory-evoked cortical activity, we characterized their modulation by sevoflurane and propofol. Power spectra and the bust-suppression ratio from EEG data were used to evaluate anaesthesia depth. ON and OFF cortical responses were elicited by light pulses of variable intensity, duration and frequency, during light and deep states of anaesthesia. Both anaesthetics reduced spontaneous cortical activity but sevoflurane greatly enhanced while propofol diminished the ON visual response. Interestingly, the large potentiation of the ON visual response by sevoflurane was found to represent a linear scaling of the encoding mechanism for light intensity. To the contrary, the OFF cortical visual response was depressed by both anaesthetics. The selective depression of the OFF component by sevoflurane could be converted into a robust potentiation by the pharmacological blockade of the ON pathway, suggesting that the temporal order of ON and OFF responses leads to a depression of the latter. This hypothesis agrees with the finding that the enhancement of the ON response was converted into a depression by increasing the frequency of light-pulse stimulation from 0.1 to 1 Hz. Overall, our results support the view that inactivity-dependent modulation of cortical circuits produces an increase in their responsiveness. Among the implications of our findings, the silencing of cortical circuits can boost linearly the cortical responsiveness but with negative impact on their frequency transfer and with a loss of the information content of the sensory signal.
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Affiliation(s)
- Alessandro Arena
- Università Vita-Salute San Raffaele, Milan, Italy.,Neurobiology of Learning Unit, Division of Neuroscience, San Raffaele Scientific Institute, Milan, Italy
| | - Jacopo Lamanna
- Università Vita-Salute San Raffaele, Milan, Italy.,Neurobiology of Learning Unit, Division of Neuroscience, San Raffaele Scientific Institute, Milan, Italy
| | - Marco Gemma
- Department of Neuro-anaesthesia and Neuro-intensive Care, Ospedale San Raffaele, Milan, Italy
| | - Maddalena Ripamonti
- Università Vita-Salute San Raffaele, Milan, Italy.,Neurobiology of Learning Unit, Division of Neuroscience, San Raffaele Scientific Institute, Milan, Italy
| | - Giuliano Ravasio
- Department of Veterinary Science and Public Health, Università degli Studi di Milano, Milan, Italy
| | - Vincenzo Zimarino
- Università Vita-Salute San Raffaele, Milan, Italy.,Neurobiology of Learning Unit, Division of Neuroscience, San Raffaele Scientific Institute, Milan, Italy
| | - Assunta De Vitis
- Department of Neuro-anaesthesia and Neuro-intensive Care, Ospedale San Raffaele, Milan, Italy
| | - Luigi Beretta
- Department of Neuro-anaesthesia and Neuro-intensive Care, Ospedale San Raffaele, Milan, Italy
| | - Antonio Malgaroli
- Università Vita-Salute San Raffaele, Milan, Italy.,Neurobiology of Learning Unit, Division of Neuroscience, San Raffaele Scientific Institute, Milan, Italy
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26
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Schroeder KE, Irwin ZT, Gaidica M, Nicole Bentley J, Patil PG, Mashour GA, Chestek CA. Disruption of corticocortical information transfer during ketamine anesthesia in the primate brain. Neuroimage 2016; 134:459-465. [PMID: 27095309 DOI: 10.1016/j.neuroimage.2016.04.039] [Citation(s) in RCA: 60] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2015] [Revised: 04/09/2016] [Accepted: 04/15/2016] [Indexed: 11/27/2022] Open
Abstract
The neural mechanisms of anesthetic-induced unconsciousness have yet to be fully elucidated, in part because of the diverse molecular targets of anesthetic agents. We demonstrate, using intracortical recordings in macaque monkeys, that information transfer between structurally connected cortical regions is disrupted during ketamine anesthesia, despite preserved primary sensory representation. Furthermore, transfer entropy, an information-theoretic measure of directed connectivity, decreases significantly between neuronal units in the anesthetized state. This is the first direct demonstration of a general anesthetic disrupting corticocortical information transfer in the primate brain. Given past studies showing that more commonly used GABAergic drugs inhibit surrogate measures of cortical communication, this finding suggests the potential for a common network-level mechanism of anesthetic-induced unconsciousness.
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Affiliation(s)
- Karen E Schroeder
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, Michigan, 48109
| | - Zachary T Irwin
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, Michigan, 48109
| | - Matt Gaidica
- Neuroscience Graduate Program, University of Michigan Medical School, Ann Arbor, Michigan, 48109
| | - J Nicole Bentley
- Department of Neurosurgery, University of Michigan Medical School, Ann Arbor, Michigan, 48109
| | - Parag G Patil
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, Michigan, 48109.,Department of Neurosurgery, University of Michigan Medical School, Ann Arbor, Michigan, 48109.,Department of Neurology, University of Michigan Medical School, Ann Arbor, Michigan, 48109
| | - George A Mashour
- Neuroscience Graduate Program, University of Michigan Medical School, Ann Arbor, Michigan, 48109.,Center for Consciousness Science, University of Michigan Medical School, Ann Arbor, Michigan, 48109.,Department of Anesthesiology, University of Michigan Medical School, Ann Arbor, Michigan, 48109
| | - Cynthia A Chestek
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, Michigan, 48109.,Neuroscience Graduate Program, University of Michigan Medical School, Ann Arbor, Michigan, 48109.,Center for Consciousness Science, University of Michigan Medical School, Ann Arbor, Michigan, 48109.,Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, Michigan, 48109.,Department of Robotics, University of Michigan, Ann Arbor, Michigan, 48109
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27
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Abstract
BACKGROUND Neuronal interactions are fundamental for information processing, cognition, and consciousness. Anesthetics reduce spontaneous cortical activity; however, neuronal reactivity to sensory stimuli is often preserved or augmented. How sensory stimulus-related neuronal interactions change under anesthesia has not been elucidated. In this study, the authors investigated the visual stimulus-related cortical neuronal interactions during stepwise emergence from desflurane anesthesia. METHODS Parallel spike trains were recorded with 64-contact extracellular microelectrode arrays from the primary visual cortex of chronically instrumented, unrestrained rats (N = 6) at 8, 6, 4, and 2% desflurane anesthesia and wakefulness. Light flashes were delivered to the retina by transcranial illumination at 5- to 15-s randomized intervals. Information theoretical indices, integration and interaction complexity, were calculated from the probability distribution of coincident spike patterns and used to quantify neuronal interactions before and after flash stimulation. RESULTS Integration and complexity showed significant negative associations with desflurane concentration (N = 60). Flash stimulation increased integration and complexity at all anesthetic levels (N = 60); the effect on complexity was reduced in wakefulness. During stepwise withdrawal of desflurane, the largest increase in integration (74%) and poststimulus complexity (35%) occurred before reaching 4% desflurane concentration-a level associated with the recovery of consciousness according to the rats' righting reflex. CONCLUSIONS Neuronal interactions in the cerebral cortex are augmented during emergence from anesthesia. Visual flash stimuli enhance neuronal interactions in both wakefulness and anesthesia; the increase in interaction complexity is attenuated as poststimulus complexity reaches plateau. The critical changes in cortical neuronal interactions occur during transition to consciousness.
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28
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Meyer RE. Physiologic Measures of Animal Stress during Transitional States of Consciousness. Animals (Basel) 2015; 5:702-16. [PMID: 26479382 PMCID: PMC4598702 DOI: 10.3390/ani5030380] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2015] [Revised: 07/24/2015] [Accepted: 07/30/2015] [Indexed: 11/21/2022] Open
Abstract
Determination of the humaneness of methods used to produce unconsciousness in animals, whether for anesthesia, euthanasia, humane slaughter, or depopulation, relies on our ability to assess stress, pain, and consciousness within the contexts of method and application. Determining the subjective experience of animals during transitional states of consciousness, however, can be quite difficult; further, loss of consciousness with different agents or methods may occur at substantially different rates. Stress and distress may manifest behaviorally (e.g., overt escape behaviors, approach-avoidance preferences [aversion]) or physiologically (e.g., movement, vocalization, changes in electroencephalographic activity, heart rate, sympathetic nervous system [SNS] activity, hypothalamic-pituitary axis [HPA] activity), such that a one-size-fits-all approach cannot be easily applied to evaluate methods or determine specific species applications. The purpose of this review is to discuss methods of evaluating stress in animals using physiologic methods, with emphasis on the transition between the conscious and unconscious states.
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Affiliation(s)
- Robert E Meyer
- College of Veterinary Medicine, Mississippi State University, Mississippi State, MS 39762, USA.
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29
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Abstract
Abstract
Despite considerable progress in the identification of the molecular targets of general anesthetics, it remains unclear how these drugs affect the brain at the systems level to suppress consciousness. According to recent proposals, anesthetics may achieve this feat by interfering with corticocortical top–down processes, that is, by interrupting information flow from association to early sensory cortices. Such a view entails two immediate questions. First, at which anatomical site, and by virtue of which physiological mechanism, do anesthetics interfere with top–down signals? Second, why does a breakdown of top–down signaling cause unconsciousness? While an answer to the first question can be gleaned from emerging neurophysiological evidence on dendritic signaling in cortical pyramidal neurons, a response to the second is offered by increasingly popular theoretical frameworks that place the element of prediction at the heart of conscious perception.
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Sellers KK, Bennett DV, Hutt A, Williams JH, Fröhlich F. Awake vs. anesthetized: layer-specific sensory processing in visual cortex and functional connectivity between cortical areas. J Neurophysiol 2015; 113:3798-815. [PMID: 25833839 DOI: 10.1152/jn.00923.2014] [Citation(s) in RCA: 63] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2014] [Accepted: 03/30/2015] [Indexed: 01/03/2023] Open
Abstract
During general anesthesia, global brain activity and behavioral state are profoundly altered. Yet it remains mostly unknown how anesthetics alter sensory processing across cortical layers and modulate functional cortico-cortical connectivity. To address this gap in knowledge of the micro- and mesoscale effects of anesthetics on sensory processing in the cortical microcircuit, we recorded multiunit activity and local field potential in awake and anesthetized ferrets (Mustela putoris furo) during sensory stimulation. To understand how anesthetics alter sensory processing in a primary sensory area and the representation of sensory input in higher-order association areas, we studied the local sensory responses and long-range functional connectivity of primary visual cortex (V1) and prefrontal cortex (PFC). Isoflurane combined with xylazine provided general anesthesia for all anesthetized recordings. We found that anesthetics altered the duration of sensory-evoked responses, disrupted the response dynamics across cortical layers, suppressed both multimodal interactions in V1 and sensory responses in PFC, and reduced functional cortico-cortical connectivity between V1 and PFC. Together, the present findings demonstrate altered sensory responses and impaired functional network connectivity during anesthesia at the level of multiunit activity and local field potential across cortical layers.
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Affiliation(s)
- Kristin K Sellers
- Department of Psychiatry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina; Neurobiology Curriculum, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina
| | - Davis V Bennett
- Department of Psychiatry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina
| | - Axel Hutt
- INRIA CR Nancy-Grand Est, Team Neurosys, Villers-les-Nancy, France
| | - James H Williams
- Department of Anesthesiology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina
| | - Flavio Fröhlich
- Department of Psychiatry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina; Neurobiology Curriculum, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina; Department of Cell Biology and Physiology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina; Department of Biomedical Engineering, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina; Neuroscience Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina; and Department of Neurology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina
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31
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Gok DK, Akpinar D, Hidisoglu E, Ozen S, Agar A, Yargicoglu P. The developmental effects of extremely low frequency electric fields on visual and somatosensory evoked potentials in adult rats. Electromagn Biol Med 2014; 35:65-74. [PMID: 25496054 DOI: 10.3109/15368378.2014.987923] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
The purpose of our study was to investigate the developmental effects of extremely low frequency electric fields (ELF-EFs) on visual evoked potentials (VEPs) and somatosensory-evoked potentials (SEPs) and to examine the relationship between lipid peroxidation and changes of these potentials. In this context, thiobarbituric acid reactive substances (TBARS) levels were determined as an indicator of lipid peroxidation. Wistar albino female rats were divided into four groups; Control (C), gestational (prenatal) exposure (Pr), gestational+ postnatal exposure (PP) and postnatal exposure (Po) groups. Pregnant rats of Pr and PP groups were exposed to 50 Hz electric field (EF) (12 kV/m; 1 h/day), while those of C and Po groups were placed in an inactive system during pregnancy. Following parturition, rats of PP and Po groups were exposed to ELF-EFs whereas rats of C and Pr groups were kept under the same experimental conditions without being exposed to any EF during 68 days. On postnatal day 90, rats were prepared for VEP and SEP recordings. The latencies of VEP components in all experimental groups were significantly prolonged versus C group. For SEPs, all components of PP group, P2, N2 components of Pr group and P1, P2, N2 components of Po group were delayed versus C group. As brain TBARS levels were significantly increased in Pr and Po groups, retina TBARS levels were significantly elevated in all experimental groups versus C group. In conclusion, alterations seen in evoked potentials, at least partly, could be explained by lipid peroxidation in the retina and brain.
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Affiliation(s)
- Deniz Kantar Gok
- a Department of Biophysics , Faculty of Medicine, Akdeniz University , Antalya , Turkey
| | - Deniz Akpinar
- a Department of Biophysics , Faculty of Medicine, Akdeniz University , Antalya , Turkey
| | - Enis Hidisoglu
- a Department of Biophysics , Faculty of Medicine, Akdeniz University , Antalya , Turkey
| | - Sukru Ozen
- b Department of Electrical and Electronics Engineering , Engineering Faculty, Akdeniz University , Antalya , Turkey , and
| | - Aysel Agar
- c Department of Physiology , Faculty of Medicine, Akdeniz University , Antalya , Turkey
| | - Piraye Yargicoglu
- a Department of Biophysics , Faculty of Medicine, Akdeniz University , Antalya , Turkey
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Zhang Y, Li Z, Dong H, Yu T. Effects of general anesthesia with propofol on thalamocortical sensory processing in rats. J Pharmacol Sci 2014; 126:370-81. [PMID: 25427432 DOI: 10.1254/jphs.14153fp] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022] Open
Abstract
The effects of anesthetics on the transmission and processing of sensory information within the thalamocortical pathway and the underlying mechanism are not fully understood. Using the extracellular recording technique, we investigated the changes of spontaneous and stimulation-evoked activities within and between the ventral posteromedial nucleus (VPM) and primary somatosensory cortex barrel field (S1BF) of the rat in vivo during propofol anesthesia. Spontaneous local field potentials, whiskers deflection–elicited somatosensory evoked potentials, and multi-unit activities in VPM/S1BF were assessed at different depths of propofol anesthesia. In VPM and S1BF, powers of spontaneous and stimulation-evoked activities, coupled with stimulation-evoked multi-unit, were decreased with increasing of propofol anesthesia. Cortical onset latency increased during intermediate/deep level propofol anesthesia, whereas thalamic onset latencies were not changed even at different depths of anesthesia. In addition, spontaneous and whisker deflectionevoked alpha oscillations were observed during propofol anesthesia, which is similar to sleep spindles, These data suggest that propofol affects processing of sensory information by 1) attenuating respective neuronal activities in VPM and S1BF, 2) delaying the ascending signal transmission from VPM to S1BF, and 3) inducing a natural-sleep type of anesthesia.
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Affiliation(s)
- Yi Zhang
- Department of Anesthesiology, the Affiliated Hospital of Zunyi Medical College, Guizhou Key Laboratory of Anesthesia and Organ Protection, China
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33
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Bachmann T, Hudetz AG. It is time to combine the two main traditions in the research on the neural correlates of consciousness: C = L × D. Front Psychol 2014; 5:940. [PMID: 25202297 PMCID: PMC4141455 DOI: 10.3389/fpsyg.2014.00940] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2014] [Accepted: 08/06/2014] [Indexed: 01/08/2023] Open
Abstract
Research on neural correlates of consciousness has been conducted and carried out mostly from within two relatively autonomous paradigmatic traditions – studying the specific contents of conscious experience and their brain-process correlates and studying the level of consciousness. In the present paper we offer a theoretical integration suggesting that an emphasis has to be put on understanding the mechanisms of consciousness (and not a mere correlates) and in doing this, the two paradigmatic traditions must be combined. We argue that consciousness emerges as a result of interaction of brain mechanisms specialized for representing the specific contents of perception/cognition – the data – and mechanisms specialized for regulating the level of activity of whatever data the content-carrying specific mechanisms happen to represent. Each of these mechanisms are necessary because without the contents there is no conscious experience and without the required level of activity the processed contents remain unconscious. Together the two mechanisms, when activated up to a necessary degree each, provide conditions sufficient for conscious experience to emerge. This proposal is related to pertinent experimental evidence.
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Mashour GA. Top-down mechanisms of anesthetic-induced unconsciousness. Front Syst Neurosci 2014; 8:115. [PMID: 25002838 PMCID: PMC4066704 DOI: 10.3389/fnsys.2014.00115] [Citation(s) in RCA: 81] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2014] [Accepted: 05/27/2014] [Indexed: 11/18/2022] Open
Abstract
The question of how structurally and pharmacologically diverse general anesthetics disrupt consciousness has persisted since the nineteenth century. There has traditionally been a significant focus on “bottom-up” mechanisms of anesthetic action, in terms of sensory processing, arousal systems, and structural scales. However, recent evidence suggests that the neural mechanisms of anesthetic-induced unconsciousness may involve a “top-down” process, which parallels current perspectives on the neurobiology of conscious experience itself. This article considers various arguments for top-down mechanisms of anesthetic-induced unconsciousness, with a focus on sensory processing and sleep-wake networks. Furthermore, recent theoretical work is discussed to highlight the possibility that top-down explanations may be causally sufficient, even assuming critical bottom-up events.
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Affiliation(s)
- George A Mashour
- Neuroscience Graduate Program, Department of Anesthesiology, Center for Consciousness Science, University of Michigan Medical School Ann Arbor, MI, USA
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35
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Graded defragmentation of cortical neuronal firing during recovery of consciousness in rats. Neuroscience 2014; 275:340-51. [PMID: 24952333 DOI: 10.1016/j.neuroscience.2014.06.018] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2014] [Revised: 05/28/2014] [Accepted: 06/09/2014] [Indexed: 11/21/2022]
Abstract
State-dependent neuronal firing patterns reflect changes in ongoing information processing and cortical function. A disruption of neuronal coordination has been suggested as the neural correlate of anesthesia. Here, we studied the temporal correlation patterns of ongoing spike activity, during a stepwise reduction of the volatile anesthetic desflurane, in the cerebral cortex of freely moving rats. We hypothesized that the recovery of consciousness from general anesthesia is accompanied by specific changes in the spatiotemporal pattern and correlation of neuronal activity. Sixty-four contact microelectrode arrays were chronically implanted in the primary visual cortex (contacts spanning 1.4-mm depth and 1.4-mm width) for recording of extracellular unit activity at four steady-state levels of anesthesia (8-2% desflurane) and wakefulness. Recovery of consciousness was defined as the regaining of the righting reflex (near 4%). High-intensity firing (HI) periods were segmented using a threshold (200-ms) representing the minimum in the neurons' bimodal interspike interval histogram under anesthesia. We found that the HI periods were highly fragmented in deep anesthesia and gradually transformed to a near-continuous firing pattern at wakefulness. As the anesthetic was withdrawn, HI periods became longer and increasingly correlated among the units both locally and across remote recording sites. Paradoxically, in 4 of 8 animals, HI correlation was also high at the deepest level of anesthesia (8%) when local field potentials (LFP) were burst-suppressed. We conclude that recovery from desflurane anesthesia is accompanied by a graded defragmentation of neuronal activity in the cerebral cortex. Hypersynchrony during deep anesthesia is an exception that occurs only with LFP burst suppression.
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Abstract
How does general anesthesia (GA) work? Anesthetics are pharmacological agents that target specific central nervous system receptors. Once they bind to their brain receptors, anesthetics modulate remote brain areas and end up interfering with global neuronal networks, leading to a controlled and reversible loss of consciousness. This remarkable manipulation of consciousness allows millions of people every year to undergo surgery safely most of the time. However, despite all the progress that has been made, we still lack a clear and comprehensive insight into the specific neurophysiological mechanisms of GA, from the molecular level to the global brain propagation. During the last decade, the exponential progress in neuroscience and neuro-imaging led to a significant step in the understanding of the neural correlates of consciousness, with direct consequences for clinical anesthesia. Far from shutting down all brain activity, anesthetics lead to a shift in the brain state to a distinct, highly specific and complex state, which is being increasingly characterized by modern neuro-imaging techniques. There are several clinical consequences and challenges that are arising from the current efforts to dissect GA mechanisms: the improvement of anesthetic depth monitoring, the characterization and avoidance of intra-operative awareness and post-anesthesia cognitive disorders, and the development of future generations of anesthetics.
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Affiliation(s)
- L Uhrig
- CEA, NeuroSpin center, 91191 Gif-sur-Yvette, France; Avenir-Bettencourt-Schueller, Inserm, 91191 Gif-sur-Yvette, France; Cognitive neuroimaging unit, Inserm, U992, 91191 Gif-sur-Yvette, France.
| | - S Dehaene
- CEA, NeuroSpin center, 91191 Gif-sur-Yvette, France; Cognitive neuroimaging unit, Inserm, U992, 91191 Gif-sur-Yvette, France; Collège de France, 75231 Paris, France; Université Paris-Sud, 91405 Orsay, France
| | - B Jarraya
- CEA, NeuroSpin center, 91191 Gif-sur-Yvette, France; Avenir-Bettencourt-Schueller, Inserm, 91191 Gif-sur-Yvette, France; Neuromodulation unit, department of neurosurgery, Foch Hospital, 92150 Suresnes, France; Université Versailles Saint-Quentin-en-Yvelines, 78000 Versailles, France
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Mashour GA. Cognitive unbinding: a neuroscientific paradigm of general anesthesia and related states of unconsciousness. Neurosci Biobehav Rev 2013; 37:2751-9. [PMID: 24076246 PMCID: PMC3870022 DOI: 10.1016/j.neubiorev.2013.09.009] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2013] [Revised: 09/14/2013] [Accepted: 09/18/2013] [Indexed: 11/28/2022]
Abstract
"Cognitive unbinding" refers to the impaired synthesis of specialized cognitive activities in the brain and has been proposed as a mechanistic paradigm of unconsciousness. This article draws on recent neuroscientific data to revisit the tenets and predictions of cognitive unbinding, using general anesthesia as a representative state of unconsciousness. Current evidence from neuroimaging and neurophysiology supports the proposition that cognitive unbinding is a parsimonious explanation for the direct mechanism (or "proximate cause") of anesthetic-induced unconsciousness across multiple drug classes. The relevance of cognitive unbinding to sleep, disorders of consciousness, and psychological processes is also explored. It is concluded that cognitive unbinding is a viable neuroscientific framework for unconscious processes across the fields of anesthesiology, sleep neurobiology, neurology and psychoanalysis.
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Affiliation(s)
- George A Mashour
- Associate Professor of Anesthesiology, Faculty of Neuroscience Graduate Program, University of Michigan Medical School, 1500 East Medical Center Drive, 1H247 University Hospital/SPC-5048, Ann Arbor, MI 48109-5048, USA.
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38
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Ward LM. The thalamus: gateway to the mind. WILEY INTERDISCIPLINARY REVIEWS. COGNITIVE SCIENCE 2013; 4:609-622. [DOI: 10.1002/wcs.1256] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/06/2013] [Revised: 07/31/2013] [Accepted: 08/06/2013] [Indexed: 11/10/2022]
Affiliation(s)
- Lawrence M. Ward
- Department of Psychology and Brain Research Centre; University of British Columbia; Vancouver BC Canada
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39
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Liu X, Pillay S, Li R, Vizuete JA, Pechman KR, Schmainda KM, Hudetz AG. Multiphasic modification of intrinsic functional connectivity of the rat brain during increasing levels of propofol. Neuroimage 2013; 83:581-92. [PMID: 23851326 DOI: 10.1016/j.neuroimage.2013.07.003] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2012] [Revised: 06/28/2013] [Accepted: 07/01/2013] [Indexed: 01/13/2023] Open
Abstract
The dose-dependent effects of anesthetics on brain functional connectivity are incompletely understood. Resting-state functional magnetic resonance imaging (rsfMRI) is widely used to assess the functional connectivity in humans and animals. Propofol is an anesthetic agent with desirable characteristics for functional neuroimaging in animals but its dose-dependent effects on rsfMRI functional connectivity have not been determined. Here we tested the hypothesis that brain functional connectivity undergoes specific changes in distinct neural networks at anesthetic depths associated with loss of consciousness. We acquired spontaneous blood oxygen level-dependent (BOLD) signals simultaneously with electroencephalographic (EEG) signals from rats under steady-state, intravenously administered propofol at increasing doses from light sedation to deep anesthesia (20, 40, 60, 80, and 100 mg/kg/h IV). Power spectra and burst suppression ratio were calculated from the EEG to verify anesthetic depth. Functional connectivity was determined from the whole brain correlation of BOLD data in regions of interest followed by a segmentation of the correlation maps into anatomically defined regional connectivity. We found that propofol produced multiphasic, dose dependent changes in functional connectivity of various cortical and subcortical networks. Cluster analysis predicted segregation of connectivity into two cortical and two subcortical clusters. In one cortical cluster (somatosensory and parietal), the early reduction in connectivity was followed by transient reversal; in the other cluster (sensory, motor and cingulate/retrosplenial), this rebound was absent. The connectivity of the subcortical cluster (brainstem, hippocampal and caudate) was strongly reduced, whereas that of another (hypothalamus, medial thalamus and n. basalis) did not. Subcortical connectivity increased again in deep anesthesia associated with EEG burst suppression. Regional correlation analysis confirmed the breakdown of connectivity within and between specific cortical and subcortical networks with deepening propofol anesthesia. Cortical connectivity was suppressed before subcortical connectivity at a critical propofol dose associated with loss of consciousness.
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Affiliation(s)
- Xiping Liu
- Department of Anesthesiology, Medical College of Wisconsin, USA
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40
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Abstract
PURPOSE OF REVIEW Can a general anesthetic binding to its membrane receptors alter global brain activity to cause loss of consciousness? RECENT FINDINGS The identification of the neurobiological mechanisms of conscious processing in awake patients that are altered by general anesthetics and the atomic structure of the general anesthetic's binding site. SUMMARY An important feature of general anesthesia is a preferential inhibition of global feedback connectivity when general anesthetics bind to allosteric sites of gamma-aminobutyric acid receptors present in the cerebral cortex.
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Vizuete JA, Pillay S, Diba K, Ropella KM, Hudetz AG. Monosynaptic functional connectivity in cerebral cortex during wakefulness and under graded levels of anesthesia. Front Integr Neurosci 2012; 6:90. [PMID: 23091451 PMCID: PMC3469825 DOI: 10.3389/fnint.2012.00090] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2012] [Accepted: 09/20/2012] [Indexed: 11/13/2022] Open
Abstract
The balance between excitation and inhibition is considered to be of significant importance for neural computation and cognitive function. Excitatory and inhibitory functional connectivity in intact cortical neuronal networks in wakefulness and graded levels of anesthesia has not been systematically investigated. We compared monosynaptic excitatory and inhibitory spike transmission probabilities using pairwise cross-correlogram (CCG) analysis. Spikes were measured at 64 sites in the visual cortex of rats with chronically implanted microelectrode arrays during wakefulness and three levels of anesthesia produced by desflurane. Anesthesia decreased the number of active units, the number of functional connections, and the strength of excitatory connections. Connection probability (number of connections per number of active unit pairs) was unaffected until the deepest anesthesia level, at which a significant increase in the excitatory to inhibitory ratio of connection probabilities was observed. The results suggest that the excitatory–inhibitory balance is altered at an anesthetic depth associated with unconsciousness.
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Affiliation(s)
- Jeannette A Vizuete
- Department of Biomedical Engineering, Marquette University Milwaukee, WI, USA
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42
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Dhanani NM, Jiang Y. Anosmia and hypogeusia as a complication of general anesthesia. J Clin Anesth 2012; 24:231-3. [PMID: 22495083 DOI: 10.1016/j.jclinane.2011.08.005] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2010] [Revised: 08/15/2011] [Accepted: 08/27/2011] [Indexed: 10/28/2022]
Abstract
A 57 year old woman with no previous history of any sensory deficits developed anosmia and hypogeusia after general anesthesia for laparoscopic cholecystectomy, with complete recovery over 6 months. There were no other identifiable factors that may have contributed to her anosmia and hypogeusia after general anesthesia. As anosmia and hypogeusia related to anesthesia and surgery are not frequently reported, the incidence of these events related to anesthesia may be higher than expected.
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Affiliation(s)
- Nadya M Dhanani
- Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, Boston, MA 02114, USA
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43
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Abstract
Consciousness is subjective experience. During both sleep and anesthesia, consciousness is common, evidenced by dreaming. A defining feature of dreaming is that, while conscious, we do not experience our environment; we are disconnected. Besides inducing behavioral unresponsiveness, a key goal of anesthesia is to prevent the experience of surgery (connected consciousness), by inducing either unconsciousness or disconnection of consciousness from the environment. Review of the isolated forearm technique demonstrates that consciousness, connectedness, and responsiveness uncouple during anesthesia; in clinical conditions, a median 37% of patients demonstrate connected consciousness. We describe potential neurobiological constructs that can explain this phenomenon: during light anesthesia the subcortical mechanisms subserving spontaneous behavioral responsiveness are disabled but information integration within the corticothalamic network continues to produce consciousness, and unperturbed norepinephrinergic signaling maintains connectedness. These concepts emphasize the need for developing anesthetic regimens and depth of anesthesia monitors that specifically target mechanisms of consciousness, connectedness, and responsiveness.
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Affiliation(s)
- Robert D Sanders
- Department of Anaesthetics, Intensive Care & Pain Medicine, Imperial College London, London, United Kingdom.
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44
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Preferential inhibition of frontal-to-parietal feedback connectivity is a neurophysiologic correlate of general anesthesia in surgical patients. PLoS One 2011; 6:e25155. [PMID: 21998638 PMCID: PMC3187752 DOI: 10.1371/journal.pone.0025155] [Citation(s) in RCA: 164] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2011] [Accepted: 08/26/2011] [Indexed: 11/19/2022] Open
Abstract
Background The precise mechanism and optimal measure of anesthetic-induced unconsciousness has yet to be elucidated. Preferential inhibition of feedback connectivity from frontal to parietal brain networks is one potential neurophysiologic correlate, but has only been demonstrated in animals or under limited conditions in healthy volunteers. Methods and Findings We recruited eighteen patients presenting for surgery under general anesthesia; electroencephalography of the frontal and parietal regions was acquired during (i) baseline consciousness, (ii) anesthetic induction with propofol or sevoflurane, (iii) general anesthesia, (iv) recovery of consciousness, and (v) post-recovery states. We used two measures of effective connectivity, evolutional map approach and symbolic transfer entropy, to analyze causal interactions of the frontal and parietal regions. The dominant feedback connectivity of the baseline conscious state was inhibited after anesthetic induction and during general anesthesia, resulting in reduced asymmetry of feedback and feedforward connections in the frontoparietal network. Dominant feedback connectivity returned when patients recovered from anesthesia. Both analytic techniques and both classes of anesthetics demonstrated similar results in this heterogeneous population of surgical patients. Conclusions The disruption of dominant feedback connectivity in the frontoparietal network is a common neurophysiologic correlate of general anesthesia across two anesthetic classes and two analytic measures. This study represents a key translational step from the underlying cognitive neuroscience of consciousness to more sophisticated monitoring of anesthetic effects in human surgical patients.
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45
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Meyer K. Primary sensory cortices, top-down projections and conscious experience. Prog Neurobiol 2011; 94:408-17. [PMID: 21683755 DOI: 10.1016/j.pneurobio.2011.05.010] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2011] [Revised: 05/20/2011] [Accepted: 05/20/2011] [Indexed: 10/18/2022]
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Cambiaghi M, Teneud L, Velikova S, Gonzalez-Rosa JJ, Cursi M, Comi G, Leocani L. Flash visual evoked potentials in mice can be modulated by transcranial direct current stimulation. Neuroscience 2011; 185:161-5. [PMID: 21515340 DOI: 10.1016/j.neuroscience.2011.04.022] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2010] [Revised: 04/08/2011] [Accepted: 04/11/2011] [Indexed: 11/27/2022]
Abstract
Transcranial direct current stimulation (tDCS) in humans has been shown to affect the size of visual evoked potentials (VEPs) in a polarity-dependent way. VEPs have been widely employed in mice to study the visual system in physiological and pathological conditions and are extensively used as animal models of neurological and visual disorders. The present study was performed to evaluate whether mice VEPs could be modulated by tDCS in the same manner as in humans. We describe here the effects of 10 min tDCS (anodal, cathodal or no stimulation) on flash-VEPs in C57BL/6 mice under sevoflurane anesthesia. VEP amplitudes of the first major peak (P1) were analyzed before, at 0, 5 and 10 min after tDCS. Compared with no stimulation condition, anodal tDCS increased P1 amplitude slightly more than 25%, while cathodal stimulation had opposite effects, with a decrease of P1 amplitude by about 30%. After-effects tended to reverse toward basal levels within 10 min after tDCS. These results, suggesting polarity-dependent modulation similar to what described in humans of tDCS effects on VEPs, encourage the use of mice models to study tDCS mechanisms of action and explore therapeutic applications on neurological models of disease.
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Affiliation(s)
- M Cambiaghi
- San Raffaele Scientific Institute, Vita-Salute San Raffaele University, Institute of Experimental Neurology (INSPE), Experimental Neurophysiology Unit, Milan, Italy
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47
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Ward LM. The thalamic dynamic core theory of conscious experience. Conscious Cogn 2011; 20:464-86. [PMID: 21349742 DOI: 10.1016/j.concog.2011.01.007] [Citation(s) in RCA: 91] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2010] [Revised: 01/19/2011] [Accepted: 01/21/2011] [Indexed: 10/18/2022]
Abstract
I propose that primary conscious awareness arises from synchronized activity in dendrites of neurons in dorsal thalamic nuclei, mediated particularly by inhibitory interactions with thalamic reticular neurons. In support, I offer four evidential pillars: (1) consciousness is restricted to the results of cortical computations; (2) thalamus is the common locus of action of brain injury in vegetative state and of general anesthetics; (3) the anatomy and physiology of the thalamus imply a central role in consciousness; (4) neural synchronization is a neural correlate of consciousness.
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Affiliation(s)
- Lawrence M Ward
- Department of Psychology, University of British Columbia, 2136 West Mall, Vancouver, BC, Canada V6T 1Z4.
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48
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Lee U, Oh G, Kim S, Noh G, Choi B, Mashour GA. Brain networks maintain a scale-free organization across consciousness, anesthesia, and recovery: evidence for adaptive reconfiguration. Anesthesiology 2010; 113:1081-91. [PMID: 20881595 PMCID: PMC2962769 DOI: 10.1097/aln.0b013e3181f229b5] [Citation(s) in RCA: 70] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
BACKGROUND Loss of consciousness is an essential feature of general anesthesia. Although alterations of neural networks during anesthesia have been identified in the spatial domain, there has been relatively little study of temporal organization. METHODS Ten healthy male volunteers were anesthetized with an induction dose of propofol on two separate occasions. The duration of network connections in the brain was analyzed by multichannel electroencephalography and the minimum spanning tree method. Entropy of the connections was calculated based on Shannon entropy. The global temporal configuration of networks was investigated by constructing the cumulative distribution function of connection times in different frequency bands and different states of consciousness. RESULTS General anesthesia was associated with a significant reduction in the number of network connections, as well as significant alterations of their duration. These changes were most prominent in the δ bandwidth and were also associated with a significant reduction in entropy of the connection matrix. Despite these and other changes, a global "scale-free" organization was consistently preserved across multiple subjects, anesthetic exposures, states of consciousness, and electroencephalogram frequencies. CONCLUSIONS Our data suggest a fundamental principle of temporal organization of network connectivity that is maintained during consciousness and anesthesia, despite local changes. These findings are consistent with a process of adaptive reconfiguration during general anesthesia.
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Affiliation(s)
- UnCheol Lee
- Post-doctoral Research Fellow, Department of Anesthesiology, University of Michigan Medical School, Ann Arbor, MI
| | - GabJin Oh
- Assistant Professor, Department of Management, Chosun University, Gwangju 501-759, Korea
| | - Seunghwan Kim
- Professor, Asia Pacific Center for Theoretical Physics & Nonlinear Complex Systems Laboratory, NCRS-SBD, Department of Physics, POSTECH, Pohang 790-784, Korea
| | - GyuJung Noh
- Professor and Chair, Department of Clinical Pharmacology and Therapeutics, Department of Anesthesiology and Pain Medicine, Asan Medical Center, University of Ulsan College of Medicine, Seoul 138-736, Korea
| | - ByungMoon Choi
- Public Health Physician, Department of Anesthesiology and Pain Medicine, National Medical Center, Seoul 100-799, Korea
| | - George A. Mashour
- Assistant Professor of Anesthesiology and Neurosurgery; Director, Division of Neuroanesthesiology; Associate Director, Anesthesiology Residency Program; University of Michigan Medical School. 1H247 UH/Box 5048, 1500 East Medical Center Drive, Ann Arbor, MI 48109-5048, Tel: 734-936-4280, Fax: 734-936-9091, ()
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Kreuzer M, Hentschke H, Antkowiak B, Schwarz C, Kochs EF, Schneider G. Cross-approximate entropy of cortical local field potentials quantifies effects of anesthesia--a pilot study in rats. BMC Neurosci 2010; 11:122. [PMID: 20863382 PMCID: PMC2955690 DOI: 10.1186/1471-2202-11-122] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2010] [Accepted: 09/23/2010] [Indexed: 12/02/2022] Open
Abstract
Background Anesthetics dose-dependently shift electroencephalographic (EEG) activity towards high-amplitude, slow rhythms, indicative of a synchronization of neuronal activity in thalamocortical networks. Additionally, they uncouple brain areas in higher (gamma) frequency ranges possibly underlying conscious perception. It is currently thought that both effects may impair brain function by impeding proper information exchange between cortical areas. But what happens at the local network level? Local networks with strong excitatory interconnections may be more resilient towards global changes in brain rhythms, but depend heavily on locally projecting, inhibitory interneurons. As anesthetics bias cortical networks towards inhibition, we hypothesized that they may cause excessive synchrony and compromise information processing already on a small spatial scale. Using a recently introduced measure of signal independence, cross-approximate entropy (XApEn), we investigated to what degree anesthetics synchronized local cortical network activity. We recorded local field potentials (LFP) from the somatosensory cortex of three rats chronically implanted with multielectrode arrays and compared activity patterns under control (awake state) with those at increasing concentrations of isoflurane, enflurane and halothane. Results Cortical LFP signals were more synchronous, as expressed by XApEn, in the presence of anesthetics. Specifically, XApEn was a monotonously declining function of anesthetic concentration. Isoflurane and enflurane were indistinguishable; at a concentration of 1 MAC (the minimum alveolar concentration required to suppress movement in response to noxious stimuli in 50% of subjects) both volatile agents reduced XApEn by about 70%, whereas halothane was less potent (50% reduction). Conclusions The results suggest that anesthetics strongly diminish the independence of operation of local cortical neuronal populations, and that the quantification of these effects in terms of XApEn has a similar discriminatory power as changes of spontaneous action potential rates. Thus, XApEn of field potentials recorded from local cortical networks provides valuable information on the anesthetic state of the brain.
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Affiliation(s)
- Matthias Kreuzer
- Department of Anesthesiology, Klinikum rechts der Isar, Technische Universität München, München, Germany
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Breakdown in cortical effective connectivity during midazolam-induced loss of consciousness. Proc Natl Acad Sci U S A 2010; 107:2681-6. [PMID: 20133802 DOI: 10.1073/pnas.0913008107] [Citation(s) in RCA: 353] [Impact Index Per Article: 25.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
By employing transcranial magnetic stimulation (TMS) in combination with high-density electroencephalography (EEG), we recently reported that cortical effective connectivity is disrupted during early non-rapid eye movement (NREM) sleep. This is a time when subjects, if awakened, may report little or no conscious content. We hypothesized that a similar breakdown of cortical effective connectivity may underlie loss of consciousness (LOC) induced by pharmacologic agents. Here, we tested this hypothesis by comparing EEG responses to TMS during wakefulness and LOC induced by the benzodiazepine midazolam. Unlike spontaneous sleep states, a subject's level of vigilance can be monitored repeatedly during pharmacological LOC. We found that, unlike during wakefulness, wherein TMS triggered responses in multiple cortical areas lasting for >300 ms, during midazolam-induced LOC, TMS-evoked activity was local and of shorter duration. Furthermore, a measure of the propagation of evoked cortical currents (significant current scattering, SCS) could reliably discriminate between consciousness and LOC. These results resemble those observed in early NREM sleep and suggest that a breakdown of cortical effective connectivity may be a common feature of conditions characterized by LOC. Moreover, these results suggest that it might be possible to use TMS-EEG to assess consciousness during anesthesia and in pathological conditions, such as coma, vegetative state, and minimally conscious state.
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