1
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Lefebvre J, Hutt A. Induced synchronization by endogenous noise modulation in finite-size random neural networks: A stochastic mean-field study. CHAOS (WOODBURY, N.Y.) 2023; 33:123110. [PMID: 38055720 DOI: 10.1063/5.0167771] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/14/2023] [Accepted: 11/09/2023] [Indexed: 12/08/2023]
Abstract
Event-related synchronization and desynchronization (ERS/ERD) are well-known features found experimentally in brain signals during cognitive tasks. Their understanding promises to have much better insights into neural information processes in cognition. Under the hypothesis that neural information affects the endogenous neural noise level in populations, we propose to employ a stochastic mean-field model to explain ERS/ERD in the γ-frequency range. The work extends previous mean-field studies by deriving novel effects from finite network size. Moreover, numerical simulations of ERS/ERD and their analytical explanation by the mean-field model suggest several endogenous noise modulation schemes, which may modulate the system's synchronization.
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Affiliation(s)
- J Lefebvre
- Krembil Brain Institute, University Health Network, Toronto, Ontario M5T 0S8, Canada
- Department of Biology, University of Ottawa, Ottawa, Ontario K1N 6N5, Canada
- Department of Mathematics, University of Toronto, Toronto, Ontario M5S 2E4, Canada
| | - A Hutt
- ICube, MLMS, University of Strasbourg, MIMESIS Team, Inria Nancy-Grand Est, 67000 Strasbourg, France
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2
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Mathematical Model Insights into EEG Origin under Transcranial Direct Current Stimulation (tDCS) in the Context of Psychosis. J Clin Med 2022; 11:jcm11071845. [PMID: 35407453 PMCID: PMC8999473 DOI: 10.3390/jcm11071845] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2022] [Revised: 03/12/2022] [Accepted: 03/22/2022] [Indexed: 02/04/2023] Open
Abstract
Schizophrenia is a psychotic disease that develops progressively over years with a transition from prodromal to psychotic state associated with a disruption in brain activity. Transcranial Direct Current Stimulation (tDCS), known to alleviate pharmaco-resistant symptoms in patients suffering from schizophrenia, promises to prevent such a psychotic transition. To understand better how tDCS affects brain activity, we propose a neural cortico-thalamo-cortical (CTC) circuit model involving the Ascending Reticular Arousal System (ARAS) that permits to describe major impact features of tDCS, such as excitability for short-duration stimulation and electroencephalography (EEG) power modulation for long-duration stimulation. To this end, the mathematical model relates stimulus duration and Long-Term Plasticity (LTP) effect, in addition to describing the temporal LTP decay after stimulus offset. This new relation promises to optimize future stimulation protocols. Moreover, we reproduce successfully EEG-power modulation under tDCS in a ketamine-induced psychosis model and confirm the N-methyl-d-aspartate (NMDA) receptor hypofunction hypothesis in the etiopathophysiology of schizophrenia. The model description points to an important role of the ARAS and the δ-rhythm synchronicity in CTC circuit in early-stage psychosis.
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3
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Liu Y, Chen B, Cai Y, Han Y, Xia Y, Li N, Fan B, Yuan T, Jiang J, Gao PO, Yu W, Jiao Y, Li W. Activation of anterior thalamic reticular nucleus GABAergic neurons promotes arousal from propofol anesthesia in mice. Acta Biochim Biophys Sin (Shanghai) 2021; 53:883-892. [PMID: 33929026 DOI: 10.1093/abbs/gmab056] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2021] [Indexed: 11/14/2022] Open
Abstract
Propofol is widely used for the induction and maintenance of anesthesia, which causes a rapid loss of consciousness. However, the mechanisms underlying the hypnosis effect of propofol are still not fully understood. The thalamic reticular nucleus (TRN) is crucial for regulating wakefulness, sleep rhythm generation, and sleep stability, while the role of TRN in the process of propofol-induced anesthesia is still unknown. Here, we investigated the function of the anterior TRN in propofol general anesthesia. Our results demonstrated that the neural activity of anterior TRN is suppressed during propofol anesthesia, whereas it is robustly activated from anesthesia by recording the calcium signals using fiber photometry technology. The results showed that the activation of anterior TRN neurons by chemogenetic and optogenetic methods shortens the emergency time without changing the induction time. Conversely, chemogenetic or optogenetic inhibition of the TRN neurons leads to a delay in the recovery time. Our study showed that anterior TRN is crucial for behavioral arousal without affecting the induction time of propofol anesthesia.
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Affiliation(s)
- Yanjun Liu
- Department of Anesthesiology, Eye and ENT Hospital, Fudan University, Shanghai 200031, China
| | - Bing Chen
- Department of Anesthesiology, Eye and ENT Hospital, Fudan University, Shanghai 200031, China
| | - Yirong Cai
- Department of Anesthesiology, Eye and ENT Hospital, Fudan University, Shanghai 200031, China
| | - Yuan Han
- Department of Anesthesiology, Eye and ENT Hospital, Fudan University, Shanghai 200031, China
| | - Ying Xia
- Department of Anesthesiology, Eye and ENT Hospital, Fudan University, Shanghai 200031, China
| | - Nanqi Li
- Department of Anesthesiology, Eye and ENT Hospital, Fudan University, Shanghai 200031, China
| | - Bingqian Fan
- Department of Anesthesiology, Eye and ENT Hospital, Fudan University, Shanghai 200031, China
| | - Tianjie Yuan
- Department of Anesthesiology, Eye and ENT Hospital, Fudan University, Shanghai 200031, China
| | - Junli Jiang
- Department of Anesthesiology, Renji Hospital, School of Medicine, Shanghai Jiaotong University, Shanghai 200127, China
| | - P o Gao
- Department of Anesthesiology, Renji Hospital, School of Medicine, Shanghai Jiaotong University, Shanghai 200127, China
| | - Weifeng Yu
- Department of Anesthesiology, Renji Hospital, School of Medicine, Shanghai Jiaotong University, Shanghai 200127, China
| | - Yingfu Jiao
- Department of Anesthesiology, Renji Hospital, School of Medicine, Shanghai Jiaotong University, Shanghai 200127, China
| | - Wenxian Li
- Department of Anesthesiology, Eye and ENT Hospital, Fudan University, Shanghai 200031, China
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4
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Arousal Fluctuations Govern Oscillatory Transitions Between Dominant [Formula: see text] and [Formula: see text] Occipital Activity During Eyes Open/Closed Conditions. Brain Topogr 2021; 35:108-120. [PMID: 34160731 DOI: 10.1007/s10548-021-00855-z] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2020] [Accepted: 06/07/2021] [Indexed: 10/21/2022]
Abstract
Arousal results in widespread activation of brain areas to increase their response in task and behavior relevant ways. Mediated by the Ascending Reticular Arousal System (ARAS), arousal-dependent inputs interact with neural circuitry to shape their dynamics. In the occipital cortex, such inputs may trigger shifts between dominant oscillations, where [Formula: see text] activity is replaced by [Formula: see text] activity, or vice versa. A salient example of this are spectral power alternations observed while eyes are opened and/or closed. These transitions closely follow fluctuations in arousal, suggesting a common origin. To better understand the mechanisms at play, we developed and analyzed a computational model composed of two modules: a thalamocortical feedback circuit coupled with a superficial cortical network. Upon activation by noise-like inputs originating from the ARAS, our model is able to demonstrate that noise-driven non-linear interactions mediate transitions in dominant peak frequency, resulting in the simultaneous suppression of [Formula: see text] limit cycle activity and the emergence of [Formula: see text] oscillations through coherence resonance. Reduction in input provoked the reverse effect - leading to anticorrelated transitions between [Formula: see text] and [Formula: see text] power. Taken together, these results shed a new light on how arousal shapes oscillatory brain activity.
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5
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Wang J, Deng B, Gao T, Wang J, Yi G, Wang R. Frequency-dependent response in cortical network with periodic electrical stimulation. CHAOS (WOODBURY, N.Y.) 2020; 30:073130. [PMID: 32752642 DOI: 10.1063/5.0007006] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/09/2020] [Accepted: 06/24/2020] [Indexed: 06/11/2023]
Abstract
Electrical stimulation can shape oscillations in brain activity. However, the mechanism of how periodic electrical stimulation modulates brain oscillations by time-delayed neural networks is poorly understood at present. To address this question, we investigate the effects of periodic stimulations on the oscillations generated via a time-delayed neural network. We specifically study the effect of unipolar and asymmetric bidirectional pulse stimulations by altering amplitude and frequency in a systematic manner. Our findings suggest that electrical stimulations play a central role in altering oscillations in the time-delayed neural network and that these alterations are strongly dependent on the stimulus frequency. We observe that the time-delayed neural network responds differently as the stimulation frequency is altered, as manifested by changes in resonance, entrainment, non-linear oscillation, or oscillation suppression. The results also indicate that the network presents similar response activities with increasing stimulus frequency under different excitation-inhibition ratios. Collectively, our findings pave the way for exploring the potential mechanism underlying the frequency-dependent modulation of network activity via electrical stimulations and provide new insights into possible electrical stimulation therapies to the neurological and psychological disorders in clinical practice.
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Affiliation(s)
- Jixuan Wang
- School of Electrical and Information Engineering, Tianjin University, 300072 Tianjin, China
| | - Bin Deng
- School of Electrical and Information Engineering, Tianjin University, 300072 Tianjin, China
| | - Tianshi Gao
- School of Electrical and Information Engineering, Tianjin University, 300072 Tianjin, China
| | - Jiang Wang
- School of Electrical and Information Engineering, Tianjin University, 300072 Tianjin, China
| | - Guosheng Yi
- School of Electrical and Information Engineering, Tianjin University, 300072 Tianjin, China
| | - Ruofan Wang
- School of Information Technology Engineering, Tianjin University of Technology and Education, 300222 Tianjin, China
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6
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Song JL, Paixao L, Li Q, Li SH, Zhang R, Westover MB. A novel neural computational model of generalized periodic discharges in acute hepatic encephalopathy. J Comput Neurosci 2019; 47:109-124. [PMID: 31506807 PMCID: PMC6881550 DOI: 10.1007/s10827-019-00727-3] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2018] [Revised: 08/12/2019] [Accepted: 08/19/2019] [Indexed: 01/13/2023]
Abstract
Acute hepatic encephalopathy (AHE) due to acute liver failure is a common form of delirium, a state of confusion, impaired attention, and decreased arousal. The electroencephalogram (EEG) in AHE often exhibits a striking abnormal pattern of brain activity, which epileptiform discharges repeat in a regular repeating pattern. This pattern is known as generalized periodic discharges, or triphasic-waves (TPWs). While much is known about the neurophysiological mechanisms underlying AHE, how these mechanisms relate to TPWs is poorly understood. In order to develop hypotheses how TPWs arise, our work builds a computational model of AHE (AHE-CM), based on three modifications of the well-studied Liley model which emulate mechanisms believed central to brain dysfunction in AHE: increased neuronal excitability, impaired synaptic transmission, and enhanced postsynaptic inhibition. To relate our AHE-CM to clinical EEG data from patients with AHE, we design a model parameter optimization method based on particle filtering (PF-POM). Based on results from 7 AHE patients, we find that the proposed AHE-CM not only performs well in reproducing important aspects of the EEG, namely the periodicity of triphasic waves (TPWs), but is also helpful in suggesting mechanisms underlying variation in EEG patterns seen in AHE. In particular, our model helps explain what conditions lead to increased frequency of TPWs. In this way, our model represents a starting point for exploring the underlying mechanisms of brain dynamics in delirium by relating microscopic mechanisms to EEG patterns.
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Affiliation(s)
- Jiang-Ling Song
- The Medical Big Data Research Center, Northwest University, Xi'an, 710127, China
- The Department of Neurology, Massachusetts General Hospital, Boston, MA, USA
| | - Luis Paixao
- The Department of Neurology, Massachusetts General Hospital, Boston, MA, USA
| | - Qiang Li
- The Medical Big Data Research Center, Northwest University, Xi'an, 710127, China
| | - Si-Hui Li
- The Medical Big Data Research Center, Northwest University, Xi'an, 710127, China
| | - Rui Zhang
- The Medical Big Data Research Center, Northwest University, Xi'an, 710127, China
| | - M Brandon Westover
- The Department of Neurology, Massachusetts General Hospital, Boston, MA, USA.
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7
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Yin L, Li L, Deng J, Wang D, Guo Y, Zhang X, Li H, Zhao S, Zhong H, Dong H. Optogenetic/Chemogenetic Activation of GABAergic Neurons in the Ventral Tegmental Area Facilitates General Anesthesia via Projections to the Lateral Hypothalamus in Mice. Front Neural Circuits 2019; 13:73. [PMID: 31798420 PMCID: PMC6878851 DOI: 10.3389/fncir.2019.00073] [Citation(s) in RCA: 29] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2019] [Accepted: 10/31/2019] [Indexed: 12/26/2022] Open
Abstract
The ventral tegmental area (VTA) reportedly regulates sleep and wakefulness through communication with the lateral hypothalamus (LH). It has also been suggested that adequate anesthesia produced by administration of chloral hydrate, ketamine, or halothane significantly reduces the GABAergic neuronal firing rate within the VTA. However, the exact effects on GABAergic neurons in the VTA and the mechanisms through which these neurons modulate anesthesia through associated neural circuits is still unclear. Here, we used optogenetic and chemogenetic methods to specifically activate or inhibit GABAergic neuronal perikarya in the VTA or their projections to the LH in Vgat-Cre mice. Electroencephalogram (EEG) spectral analyses and burst suppression ratio (BSR) calculations were conducted following administration of 0.8 or 1.0% isoflurane, respectively; and loss of righting reflex (LORR), recovery of righting reflex (RORR), and anesthesia sensitivity were assessed under 1.4% isoflurane anesthesia. The results showed that activation of GABAergic neurons in the VTA increased delta wave power from 40.0 to 46.4% (P = 0.006) and decreased gamma wave power from 15.2 to 11.5% (P = 0.017) during anesthesia maintenance. BSR was increased from 51.8 to 68.3% (P = 0.017). Induction time (LORR) was reduced from 333 to 290 s (P = 0.019), whereas arousal time (RORR) was prolonged from 498 to 661 s (P = 0.007). Conversely, inhibition of VTA GABAergic neurons led to opposite effects. In contrast, optical activation of VTA-LH GABAergic projection neurons increased power of slow delta waves from 44.2 to 48.8% (P = 0.014) and decreased that of gamma oscillations from 10.2 to 8.0%. BSR was increased from 39.9 to 60.2% (P = 0.0002). LORR was reduced from 330 to 232 s (P = 0.002), and RORR increased from 396 to 565 s (P = 0.007). Optical inhibition of the projection neurons caused opposite effects in terms of both the EEG spectrum and the BSR, except that inhibition of this projection did not accelerate arousal time. These results indicate that VTA GABAergic neurons could facilitate the anesthetic effects of isoflurane during induction and maintenance while postponing anesthetic recovery, at least partially, through modulation of their projections to the LH.
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Affiliation(s)
- Lu Yin
- Department of Anesthesiology and Perioperative Medicine, Xijing Hospital, The Fourth Military Medical University, Xi'an, China
| | - Long Li
- Department of Anesthesiology and Perioperative Medicine, Xijing Hospital, The Fourth Military Medical University, Xi'an, China
| | - Jiao Deng
- Department of Anesthesiology and Perioperative Medicine, Xijing Hospital, The Fourth Military Medical University, Xi'an, China
| | - Dan Wang
- Department of Anesthesiology and Perioperative Medicine, Xijing Hospital, The Fourth Military Medical University, Xi'an, China
| | - YongXin Guo
- Department of Anesthesiology and Perioperative Medicine, Xijing Hospital, The Fourth Military Medical University, Xi'an, China
| | - XinXin Zhang
- Department of Anesthesiology and Perioperative Medicine, Xijing Hospital, The Fourth Military Medical University, Xi'an, China
| | - HuiMing Li
- Department of Anesthesiology and Perioperative Medicine, Xijing Hospital, The Fourth Military Medical University, Xi'an, China
| | - ShiYi Zhao
- Department of Anesthesiology and Perioperative Medicine, Xijing Hospital, The Fourth Military Medical University, Xi'an, China
| | - HaiXing Zhong
- Department of Anesthesiology and Perioperative Medicine, Xijing Hospital, The Fourth Military Medical University, Xi'an, China
| | - HaiLong Dong
- Department of Anesthesiology and Perioperative Medicine, Xijing Hospital, The Fourth Military Medical University, Xi'an, China
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8
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Cortico-Thalamic Circuit Model for Bottom-Up and Top-Down Mechanisms in General Anesthesia Involving the Reticular Activating System. ARCHIVES OF NEUROSCIENCE 2019. [DOI: 10.5812/ans.95498] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
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9
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Toropova AP, Toropov AA, Benfenati E. Semi-correlations as a tool to build up categorical (active/inactive) model of GABAA receptor modulator activity. Struct Chem 2018. [DOI: 10.1007/s11224-018-1226-x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
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10
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Bukoski A, Steyn-Ross DA, Pickett AF, Steyn-Ross ML. Anesthesia modifies subthreshold critical slowing down in a stochastic Hodgkin-Huxley-like model with inhibitory synaptic input. Phys Rev E 2018; 97:062403. [PMID: 30011536 DOI: 10.1103/physreve.97.062403] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2018] [Indexed: 11/07/2022]
Abstract
The dynamics of a stochastic type-I Hodgkin-Huxley-like point neuron model exposed to inhibitory synaptic noise are investigated as a function of distance from spiking threshold and the inhibitory influence of the general anesthetic agent propofol. The model is biologically motivated and includes the effects of intrinsic ion-channel noise via a stochastic differential equation description as well as inhibitory synaptic noise modeled as multiple Poisson-distributed impulse trains with saturating response functions. The effect of propofol on these synapses is incorporated through this drug's principal influence on fast inhibitory neurotransmission mediated by γ-aminobutyric acid (GABA) type-A receptors via reduction of the synaptic response decay rate. As the neuron model approaches spiking threshold from below, we track membrane voltage fluctuation statistics of numerically simulated stochastic trajectories. We find that for a given distance from spiking threshold, increasing the magnitude of anesthetic-induced inhibition is associated with augmented signatures of critical slowing: fluctuation amplitudes and correlation times grow as spectral power is increasingly focused at 0 Hz. Furthermore, as a function of distance from threshold, anesthesia significantly modifies the power-law exponents for variance and correlation time divergences observable in stochastic trajectories. Compared to the inverse square root power-law scaling of these quantities anticipated for the saddle-node bifurcation of type-I neurons in the absence of anesthesia, increasing anesthetic-induced inhibition results in an observable exponent <-0.5 for variance and >-0.5 for correlation time divergences. However, these behaviors eventually break down as distance from threshold goes to zero with both the variance and correlation time converging to common values independent of anesthesia. Compared to the case of no synaptic input, linearization of an approximating multivariate Ornstein-Uhlenbeck model reveals these effects to be the consequence of an additional slow eigenvalue associated with synaptic activity that competes with those of the underlying point neuron in a manner that depends on distance from spiking threshold.
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Affiliation(s)
- Alex Bukoski
- College of Veterinary Medicine, University of Missouri, Columbia, Missouri 65211, USA
| | - D A Steyn-Ross
- School of Engineering, University of Waikato, Hamilton 3240, New Zealand
| | - Ashley F Pickett
- College of Veterinary Medicine, Auburn University, Auburn, Alabama 36849, USA
| | - Moira L Steyn-Ross
- School of Engineering, University of Waikato, Hamilton 3240, New Zealand
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11
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Hutt A, Griffiths JD, Herrmann CS, Lefebvre J. Effect of Stimulation Waveform on the Non-linear Entrainment of Cortical Alpha Oscillations. Front Neurosci 2018; 12:376. [PMID: 29997467 PMCID: PMC6028725 DOI: 10.3389/fnins.2018.00376] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2018] [Accepted: 05/16/2018] [Indexed: 01/06/2023] Open
Abstract
In the past decade, there has been a surge of interest in using patterned brain stimulation to manipulate cortical oscillations, in both experimental and clinical settings. But the relationship between stimulation waveform and its impact on ongoing oscillations remains poorly understood and severely restrains the development of new paradigms. To address some aspects of this intricate problem, we combine computational and mathematical approaches, providing new insights into the influence of waveform of both low and high-frequency stimuli on synchronous neural activity. Using a cellular-based cortical microcircuit network model, we performed numerical simulations to test the influence of different waveforms on ongoing alpha oscillations, and derived a mean-field description of stimulation-driven dynamics to better understand the observed responses. Our analysis shows that high-frequency periodic stimulation translates into an effective transformation of the neurons' response function, leading to waveform-dependent changes in oscillatory dynamics and resting state activity. Moreover, we found that randomly fluctuating stimulation linearizes the neuron response function while constant input moves its activation threshold. Taken together, our findings establish a new theoretical framework in which stimulation waveforms impact neural systems at the population-scale through non-linear interactions.
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Affiliation(s)
- Axel Hutt
- Deutscher Wetterdienst, Department FE12-Data Assimilation, Offenbach am Main, Germany
| | - John D Griffiths
- Rotman Research Institute, Baycrest Health Sciences, Toronto, ON, Canada.,Krembil Research Institute, University Health Network, Toronto, ON, Canada
| | - Christoph S Herrmann
- Experimental Psychology Lab, Department of Psychology, Cluster of Excellence "Hearing4all", European Medical, School, Carl von Ossietzky University, Oldenburg, Germany
| | - Jérémie Lefebvre
- Krembil Research Institute, University Health Network, Toronto, ON, Canada.,Department of Mathematics and Institute for Biomaterials and Biomedical Engineering, University of Toronto, Toronto, ON, Canada
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12
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Hutt A, Lefebvre J, Hight D, Sleigh J. Suppression of underlying neuronal fluctuations mediates EEG slowing during general anaesthesia. Neuroimage 2018; 179:414-428. [PMID: 29920378 DOI: 10.1016/j.neuroimage.2018.06.043] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2018] [Revised: 05/03/2018] [Accepted: 06/12/2018] [Indexed: 11/25/2022] Open
Abstract
The physiological mechanisms by which anaesthetic drugs modulate oscillatory brain activity remain poorly understood. Combining human data, mathematical and computational analysis of both spiking and mean-field models, we investigated the spectral dynamics of encephalographic (EEG) beta-alpha oscillations, observed in human patients undergoing general anaesthesia. The effect of anaesthetics can be modelled as a reduction of neural fluctuation intensity, and/or an increase in inhibitory synaptic gain in the thalamo-cortical circuit. Unlike previous work, which suggested the primary importance of gamma-amino-butryic-acid (GABA) augmentation in causing a shift to low EEG frequencies, our analysis demonstrates that a non-linear transition, triggered by a simple decrease in neural fluctuation intensity, is sufficient to explain the clinically-observed appearance - and subsequent slowing - of the beta-alpha narrowband EEG peak. In our model, increased synaptic inhibition alone, did not correlate with the clinically-observed encephalographic spectral changes, but did cause the anaesthetic-induced decrease in neuronal firing rate. Taken together, our results show that such a non-linear transition results in functional fragmentation of cortical and thalamic populations; highly correlated intra-population dynamics triggered by anaesthesia decouple and isolate neural populations. Our results are able to parsimoniously unify and replicate the observed anaesthetic effects on both the EEG spectra and inter-regional connectivity, and further highlight the importance of neural activity fluctuations in the genesis of altered brain states.
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Affiliation(s)
- Axel Hutt
- Department FE 12 - Data Assimilation, Deutscher Wetterdienst, 63067, Offenbach am Main, Germany; Department of Mathematics and Statistics, University of Reading, Reading, RG6 6AX, UK.
| | - Jérémie Lefebvre
- Krembil Research Institute, University Health Network, Toronto, Ontario, M5T 2S8, Canada; Department of Mathematics, University of Toronto, Toronto, Ontario, M5T 2S8, Canada; Institute of Biomaterials and Biomedical Engineering, University of Toronto, Toronto, Ontario, M5T 2S8, Canada
| | - Darren Hight
- Department of Anaesthesiology, Waikato Clinical Campus, University of Auckland, Hamilton, 3240, New Zealand; Department of Anaesthesiology and Pain Therapy, University Hospital Bern, Inselspital, Bern, Switzerland
| | - Jamie Sleigh
- Department of Anaesthesiology, Waikato Clinical Campus, University of Auckland, Hamilton, 3240, New Zealand.
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13
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Alswaihli J, Potthast R, Bojak I, Saddy D, Hutt A. Kernel Reconstruction for Delayed Neural Field Equations. JOURNAL OF MATHEMATICAL NEUROSCIENCE 2018; 8:3. [PMID: 29399710 PMCID: PMC5797727 DOI: 10.1186/s13408-018-0058-8] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 06/26/2017] [Accepted: 01/17/2018] [Indexed: 06/07/2023]
Abstract
Understanding the neural field activity for realistic living systems is a challenging task in contemporary neuroscience. Neural fields have been studied and developed theoretically and numerically with considerable success over the past four decades. However, to make effective use of such models, we need to identify their constituents in practical systems. This includes the determination of model parameters and in particular the reconstruction of the underlying effective connectivity in biological tissues.In this work, we provide an integral equation approach to the reconstruction of the neural connectivity in the case where the neural activity is governed by a delay neural field equation. As preparation, we study the solution of the direct problem based on the Banach fixed-point theorem. Then we reformulate the inverse problem into a family of integral equations of the first kind. This equation will be vector valued when several neural activity trajectories are taken as input for the inverse problem. We employ spectral regularization techniques for its stable solution. A sensitivity analysis of the regularized kernel reconstruction with respect to the input signal u is carried out, investigating the Fréchet differentiability of the kernel with respect to the signal. Finally, we use numerical examples to show the feasibility of the approach for kernel reconstruction, including numerical sensitivity tests, which show that the integral equation approach is a very stable and promising approach for practical computational neuroscience.
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Affiliation(s)
- Jehan Alswaihli
- Department of Mathematics and Statistics, University of Reading, Reading, UK
- Department of Mathematics, Faculty of Education, Misurata University, Misurata, Libya
| | - Roland Potthast
- Department of Mathematics and Statistics, University of Reading, Reading, UK
- Division for Data Assimilation (FE12), Deutscher Wetterdienst, Offenbach, Germany
| | - Ingo Bojak
- Centre for Integrative Neuroscience and Neurodynamics (CINN), Department of Psychology, University of Reading, Reading, UK
| | - Douglas Saddy
- Centre for Integrative Neuroscience and Neurodynamics (CINN), Department of Psychology, University of Reading, Reading, UK
| | - Axel Hutt
- Department of Mathematics and Statistics, University of Reading, Reading, UK
- Division for Data Assimilation (FE12), Deutscher Wetterdienst, Offenbach, Germany
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14
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Shaping Intrinsic Neural Oscillations with Periodic Stimulation. J Neurosci 2017; 36:5328-37. [PMID: 27170129 DOI: 10.1523/jneurosci.0236-16.2016] [Citation(s) in RCA: 86] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2016] [Accepted: 04/05/2016] [Indexed: 01/07/2023] Open
Abstract
UNLABELLED Rhythmic brain activity plays an important role in neural processing and behavior. Features of these oscillations, including amplitude, phase, and spectrum, can be influenced by internal states (e.g., shifts in arousal, attention or cognitive ability) or external stimulation. Electromagnetic stimulation techniques such as transcranial magnetic stimulation, transcranial direct current stimulation, and transcranial alternating current stimulation are used increasingly in both research and clinical settings. Currently, the mechanisms whereby time-dependent external stimuli influence population-scale oscillations remain poorly understood. Here, we provide computational insights regarding the mapping between periodic pulsatile stimulation parameters such as amplitude and frequency and the response dynamics of recurrent, nonlinear spiking neural networks. Using a cortical model built of excitatory and inhibitory neurons, we explored a wide range of stimulation intensities and frequencies systematically. Our results suggest that rhythmic stimulation can form the basis of a control paradigm in which one can manipulate the intrinsic oscillatory properties of driven networks via a plurality of input-driven mechanisms. Our results show that, in addition to resonance and entrainment, nonlinear acceleration is involved in shaping the rhythmic response of our modeled network. Such nonlinear acceleration of spontaneous and synchronous oscillatory activity in a neural network occurs in regimes of intense, high-frequency rhythmic stimulation. These results open new perspectives on the manipulation of synchronous neural activity for basic and clinical research. SIGNIFICANCE STATEMENT Oscillatory activity is widely recognized as a core mechanism for information transmission within and between brain circuits. Noninvasive stimulation methods can shape this activity, something that is increasingly capitalized upon in basic research and clinical practice. Here, we provide computational insights on the mechanistic bases for such effects. Our results show that rhythmic stimulation forms the basis of a control paradigm in which one can manipulate the intrinsic oscillatory properties of driven networks via a plurality of input-driven mechanisms. In addition to resonance and entrainment, nonlinear acceleration is involved in shaping the rhythmic response of our modeled network, particularly in regimes of high-frequency rhythmic stimulation. These results open new perspectives on the manipulation of synchronous neural activity for basic and clinical research.
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Hashemi M, Hutt A, Hight D, Sleigh J. Anesthetic action on the transmission delay between cortex and thalamus explains the beta-buzz observed under propofol anesthesia. PLoS One 2017; 12:e0179286. [PMID: 28622355 PMCID: PMC5473556 DOI: 10.1371/journal.pone.0179286] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2016] [Accepted: 05/26/2017] [Indexed: 11/18/2022] Open
Abstract
In recent years, more and more surgeries under general anesthesia have been performed with the assistance of electroencephalogram (EEG) monitors. An increase in anesthetic concentration leads to characteristic changes in the power spectra of the EEG. Although tracking the anesthetic-induced changes in EEG rhythms can be employed to estimate the depth of anesthesia, their precise underlying mechanisms are still unknown. A prominent feature in the EEG of some patients is the emergence of a strong power peak in the β-frequency band, which moves to the α-frequency band while increasing the anesthetic concentration. This feature is called the beta-buzz. In the present study, we use a thalamo-cortical neural population feedback model to reproduce observed characteristic features in frontal EEG power obtained experimentally during propofol general anesthesia, such as this beta-buzz. First, we find that the spectral power peak in the α- and δ-frequency ranges depend on the decay rate constant of excitatory and inhibitory synapses, but the anesthetic action on synapses does not explain the beta-buzz. Moreover, considering the action of propofol on the transmission delay between cortex and thalamus, the model reveals that the beta-buzz may result from a prolongation of the transmission delay by increasing propofol concentration. A corresponding relationship between transmission delay and anesthetic blood concentration is derived. Finally, an analytical stability study demonstrates that increasing propofol concentration moves the systems resting state towards its stability threshold.
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Affiliation(s)
- Meysam Hashemi
- INRIA Grand Est - Nancy, Team NEUROSYS, Villers-lès-Nancy, France
- CNRS, Loria, UMR nō 7503, Vandoeuvre-lès-Nancy, France
- Université de Lorraine, Loria, UMR nō 7503, Vandoeuvre-lès-Nancy, France
- Aix Marseille Université, INSERM, INS, Institut de Neurosciences des Systèmes, Marseille, France
| | - Axel Hutt
- German Meteorology Service, Offenbach am Main, Germany
- Department of Mathematics and Statistics, University of Reading, Reading, United Kingdom
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Liu X, Gao J, Wang G, Chen ZW. Controllability Analysis of the Neural Mass Model with Dynamic Parameters. Neural Comput 2016; 29:485-501. [PMID: 28030778 DOI: 10.1162/neco_a_00925] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
Abstract
The development of control technology for the brain is of potential significance to the prevention and treatment of neuropsychiatric disorders and the improvement of humans' mental health. A controllability analysis of the brain is necessary to ensure the feasibility of the brain control. In this letter, we investigate the influences of dynamical parameters on the controllability in the neural mass model by using controllability indices as quantitative indicators. The indices are obtained by computing Lie brackets and condition numbers of the system model. We show how controllability changes with important parameters of our dynamical (neuronal) model. Our results suggest that the underlying dynamical parameters have certain ranges with better controllability. We hope it can play potential roles in therapy for brain nervous disorder disease.
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Affiliation(s)
- Xian Liu
- Key Lab of Industrial Computer Control Engineering of Hebei Province, Institute of Electrical Engineering, Yanshan University, Qinhuangdao 066004, P.R.C.
| | - Jing Gao
- Institute of Electrical Engineering, Yanshan University, Qinhuangdao 066004, P.R.C.
| | - Guan Wang
- Institute of Electrical Engineering, Yanshan University, Qinhuangdao 066004, P.R.C.
| | - Zhi-Wang Chen
- Institute of Electrical Engineering, Yanshan University, Qinhuangdao 066004, P.R.C.
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Hutt A, Mierau A, Lefebvre J. Dynamic Control of Synchronous Activity in Networks of Spiking Neurons. PLoS One 2016; 11:e0161488. [PMID: 27669018 PMCID: PMC5036852 DOI: 10.1371/journal.pone.0161488] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2016] [Accepted: 08/06/2016] [Indexed: 11/19/2022] Open
Abstract
Oscillatory brain activity is believed to play a central role in neural coding. Accumulating evidence shows that features of these oscillations are highly dynamic: power, frequency and phase fluctuate alongside changes in behavior and task demands. The role and mechanism supporting this variability is however poorly understood. We here analyze a network of recurrently connected spiking neurons with time delay displaying stable synchronous dynamics. Using mean-field and stability analyses, we investigate the influence of dynamic inputs on the frequency of firing rate oscillations. We show that afferent noise, mimicking inputs to the neurons, causes smoothing of the system’s response function, displacing equilibria and altering the stability of oscillatory states. Our analysis further shows that these noise-induced changes cause a shift of the peak frequency of synchronous oscillations that scales with input intensity, leading the network towards critical states. We lastly discuss the extension of these principles to periodic stimulation, in which externally applied driving signals can trigger analogous phenomena. Our results reveal one possible mechanism involved in shaping oscillatory activity in the brain and associated control principles.
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Affiliation(s)
- Axel Hutt
- Deutscher Wetterdienst, Section FE12 - Data Assimilation, 63067, Offenbach am Main, Germany
| | - Andreas Mierau
- Institute of Movement and Neurosciences, German Sport University, Cologne, Germany
| | - Jérémie Lefebvre
- Krembil Research Institute, University Health Network, Toronto, Ontario, M5T 2S8, Canada
- Department of Mathematics, University of Toronto, Toronto, Ontario, M5S 3G3, Canada
- * E-mail:
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Kuhlmann L, Manton JH, Heyse B, Vereecke HEM, Lipping T, Struys MMRF, Liley DTJ. Tracking Electroencephalographic Changes Using Distributions of Linear Models: Application to Propofol-Based Depth of Anesthesia Monitoring. IEEE Trans Biomed Eng 2016; 64:870-881. [PMID: 27323352 DOI: 10.1109/tbme.2016.2562261] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
OBJECTIVE Tracking brain states with electrophysiological measurements often relies on short-term averages of extracted features and this may not adequately capture the variability of brain dynamics. The objective is to assess the hypotheses that this can be overcome by tracking distributions of linear models using anesthesia data, and that anesthetic brain state tracking performance of linear models is comparable to that of a high performing depth of anesthesia monitoring feature. METHODS Individuals' brain states are classified by comparing the distribution of linear (auto-regressive moving average-ARMA) model parameters estimated from electroencephalographic (EEG) data obtained with a sliding window to distributions of linear model parameters for each brain state. The method is applied to frontal EEG data from 15 subjects undergoing propofol anesthesia and classified by the observers assessment of alertness/sedation (OAA/S) scale. Classification of the OAA/S score was performed using distributions of either ARMA parameters or the benchmark feature, Higuchi fractal dimension. RESULTS The highest average testing sensitivity of 59% (chance sensitivity: 17%) was found for ARMA (2,1) models and Higuchi fractal dimension achieved 52%, however, no statistical difference was observed. For the same ARMA case, there was no statistical difference if medians are used instead of distributions (sensitivity: 56%). CONCLUSION The model-based distribution approach is not necessarily more effective than a median/short-term average approach, however, it performs well compared with a distribution approach based on a high performing anesthesia monitoring measure. SIGNIFICANCE These techniques hold potential for anesthesia monitoring and may be generally applicable for tracking brain states.
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Kuhlmann L, Freestone DR, Manton JH, Heyse B, Vereecke HE, Lipping T, Struys MM, Liley DT. Neural mass model-based tracking of anesthetic brain states. Neuroimage 2016; 133:438-456. [DOI: 10.1016/j.neuroimage.2016.03.039] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2015] [Revised: 02/26/2016] [Accepted: 03/18/2016] [Indexed: 01/22/2023] Open
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Puelma Touzel M, Wolf F. Complete Firing-Rate Response of Neurons with Complex Intrinsic Dynamics. PLoS Comput Biol 2015; 11:e1004636. [PMID: 26720924 PMCID: PMC4697854 DOI: 10.1371/journal.pcbi.1004636] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2015] [Accepted: 10/29/2015] [Indexed: 11/23/2022] Open
Abstract
The response of a neuronal population over a space of inputs depends on the intrinsic properties of its constituent neurons. Two main modes of single neuron dynamics–integration and resonance–have been distinguished. While resonator cell types exist in a variety of brain areas, few models incorporate this feature and fewer have investigated its effects. To understand better how a resonator’s frequency preference emerges from its intrinsic dynamics and contributes to its local area’s population firing rate dynamics, we analyze the dynamic gain of an analytically solvable two-degree of freedom neuron model. In the Fokker-Planck approach, the dynamic gain is intractable. The alternative Gauss-Rice approach lifts the resetting of the voltage after a spike. This allows us to derive a complete expression for the dynamic gain of a resonator neuron model in terms of a cascade of filters on the input. We find six distinct response types and use them to fully characterize the routes to resonance across all values of the relevant timescales. We find that resonance arises primarily due to slow adaptation with an intrinsic frequency acting to sharpen and adjust the location of the resonant peak. We determine the parameter regions for the existence of an intrinsic frequency and for subthreshold and spiking resonance, finding all possible intersections of the three. The expressions and analysis presented here provide an account of how intrinsic neuron dynamics shape dynamic population response properties and can facilitate the construction of an exact theory of correlations and stability of population activity in networks containing populations of resonator neurons. Dynamic gain, the amount by which features at specific frequencies in the input to a neuron are amplified or attenuated in its output spiking, is fundamental for the encoding of information by neural populations. Most studies of dynamic gain have focused on neurons without intrinsic degrees of freedom exhibiting integrator-type subthreshold dynamics. Many neuron types in the brain, however, exhibit complex subthreshold dynamics such as resonance, found for instance in cortical interneurons, stellate cells, and mitral cells. A resonator neuron has at least two degrees of freedom for which the classical Fokker-Planck approach to calculating the dynamic gain is largely intractable. Here, we lift the voltage-reset rule after a spike, allowing us to derive a complete expression of the dynamic gain of a resonator neuron model. We find the gain can exhibit only six shapes. The resonant ones have peaks that become large due to intrinsic adaptation and become sharp due to an intrinsic frequency. A resonance can nevertheless result from either property. The analysis presented here helps explain how intrinsic neuron dynamics shape population-level response properties and provides a powerful tool for developing theories of inter-neuron correlations and dynamic responses of neural populations.
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Affiliation(s)
- Maximilian Puelma Touzel
- Department for Nonlinear Dynamics, Max Planck Institute for Dynamics and Self-Organization, Goettingen, Germany
- Bernstein Center for Computational Neuroscience, Goettingen, Germany
- Institute for Nonlinear Dynamics, Georg-August University School of Science, Goettingen, Germany
- * E-mail:
| | - Fred Wolf
- Department for Nonlinear Dynamics, Max Planck Institute for Dynamics and Self-Organization, Goettingen, Germany
- Bernstein Center for Computational Neuroscience, Goettingen, Germany
- Institute for Nonlinear Dynamics, Georg-August University School of Science, Goettingen, Germany
- Kavli Institute for Theoretical Physics, University of California Santa Barbara, Santa Barbara, California, United States of America
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Nichols EJ, Hutt A. Neural field simulator: two-dimensional spatio-temporal dynamics involving finite transmission speed. Front Neuroinform 2015; 9:25. [PMID: 26539105 PMCID: PMC4611063 DOI: 10.3389/fninf.2015.00025] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2015] [Accepted: 10/02/2015] [Indexed: 12/14/2022] Open
Abstract
Neural Field models (NFM) play an important role in the understanding of neural population dynamics on a mesoscopic spatial and temporal scale. Their numerical simulation is an essential element in the analysis of their spatio-temporal dynamics. The simulation tool described in this work considers scalar spatially homogeneous neural fields taking into account a finite axonal transmission speed and synaptic temporal derivatives of first and second order. A text-based interface offers complete control of field parameters and several approaches are used to accelerate simulations. A graphical output utilizes video hardware acceleration to display running output with reduced computational hindrance compared to simulators that are exclusively software-based. Diverse applications of the tool demonstrate breather oscillations, static and dynamic Turing patterns and activity spreading with finite propagation speed. The simulator is open source to allow tailoring of code and this is presented with an extension use case.
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Affiliation(s)
- Eric J. Nichols
- Team Neurosys, Loria, Centre National de la Recherche Scientifique, INRIA, UMR no. 7503, Université de LorraineNancy, France
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How the cortico-thalamic feedback affects the EEG power spectrum over frontal and occipital regions during propofol-induced sedation. J Comput Neurosci 2015; 39:155-79. [PMID: 26256583 DOI: 10.1007/s10827-015-0569-1] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2015] [Revised: 07/05/2015] [Accepted: 07/13/2015] [Indexed: 12/16/2022]
Abstract
Increasing concentrations of the anaesthetic agent propofol initially induces sedation before achieving full general anaesthesia. During this state of anaesthesia, the observed specific changes in electroencephalographic (EEG) rhythms comprise increased activity in the δ- (0.5-4 Hz) and α- (8-13 Hz) frequency bands over the frontal region, but increased δ- and decreased α-activity over the occipital region. It is known that the cortex, the thalamus, and the thalamo-cortical feedback loop contribute to some degree to the propofol-induced changes in the EEG power spectrum. However the precise role of each structure to the dynamics of the EEG is unknown. In this paper we apply a thalamo-cortical neuronal population model to reproduce the power spectrum changes in EEG during propofol-induced anaesthesia sedation. The model reproduces the power spectrum features observed experimentally both in frontal and occipital electrodes. Moreover, a detailed analysis of the model indicates the importance of multiple resting states in brain activity. The work suggests that the α-activity originates from the cortico-thalamic relay interaction, whereas the emergence of δ-activity results from the full cortico-reticular-relay-cortical feedback loop with a prominent enforced thalamic reticular-relay interaction. This model suggests an important role for synaptic GABAergic receptors at relay neurons and, more generally, for the thalamus in the generation of both the δ- and the α- EEG patterns that are seen during propofol anaesthesia sedation.
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Hashemi M, Hutt A, Sleigh J. Anesthetic action on extra-synaptic receptors: effects in neural population models of EEG activity. Front Syst Neurosci 2014; 8:232. [PMID: 25540612 PMCID: PMC4261904 DOI: 10.3389/fnsys.2014.00232] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2014] [Accepted: 11/19/2014] [Indexed: 12/13/2022] Open
Abstract
The role of extra-synaptic receptors in the regulation of excitation and inhibition in the brain has attracted increasing attention. Because activity in the extra-synaptic receptors plays a role in regulating the level of excitation and inhibition in the brain, they may be important in determining the level of consciousness. This paper reviews briefly the literature on extra-synaptic GABA and NMDA receptors and their affinity to anesthetic drugs. We propose a neural population model that illustrates how the effect of the anesthetic drug propofol on GABAergic extra-synaptic receptors results in changes in neural population activity and the electroencephalogram (EEG). Our results show that increased tonic inhibition in inhibitory cortical neurons cause a dramatic increase in the power of both δ− and α− bands. Conversely, the effects of increased tonic inhibition in cortical excitatory neurons and thalamic relay neurons have the opposite effect and decrease the power in these bands. The increased δ-activity is in accord with observed data for deepening propofol anesthesia; but is absolutely dependent on the inclusion of extrasynaptic (tonic) GABA action in the model.
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Affiliation(s)
- Meysam Hashemi
- INRIA CR Nancy - Grand Est, Team Neurosys Villers-les-Nancy, France
| | - Axel Hutt
- INRIA CR Nancy - Grand Est, Team Neurosys Villers-les-Nancy, France
| | - Jamie Sleigh
- Department of Anaesthesiology, Waikato Clinical School, University of Auckland Hamilton, New Zealand
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