The sensory thalamus and cerebral motor cortex are affected concurrently during induction of anesthesia with propofol: a case series with intracranial electroencephalogram recordings

Globus pallidus externus drives increase in network-wide alpha power with propofol-induced loss-of-consciousness in humans

States of consciousness are likely mediated by multiple parallel yet interacting cortico-subcortical recurrent networks. Although the mesocircuit model has implicated the pallidocortical circuit as one such network, this circuit has not been extensively evaluated to identify network-level electrophysiological changes related to loss of consciousness (LOC). We characterize changes in the mesocircuit in awake versus propofol-induced LOC in humans by directly simultaneously recording from sensorimotor cortices (S1/M1) and globus pallidus interna and externa (GPi/GPe) in 12 patients with Parkinson disease undergoing deep brain stimulator implantation. Propofol-induced LOC is associated with increases in local power up to 20 Hz in GPi, 35 Hz in GPe, and 100 Hz in S1/M1. LOC is likewise marked by increased pallidocortical alpha synchrony across all nodes, with increased alpha/low beta Granger causal (GC) flow from GPe to all other nodes. In contrast, LOC is associated with decreased network-wide beta coupling and beta GC from M1 to the rest of the network. Results implicate an important and possibly central role of GPe in mediating LOC-related increases in alpha power, supporting a significant role of the GPe in modulating cortico-subcortical circuits for consciousness. Simultaneous LOC-related suppression of beta synchrony highlights that distinct oscillatory frequencies act independently, conveying unique network activity.

Propofol-induced loss of consciousness is associated with a decrease in thalamocortical connectivity in humans

Although the molecular effects of many anaesthetics have been well characterized, a network-level explanation for how these changes lead to loss of consciousness remains unclear. Studies using electroencephalography have characterized changes in neural oscillations in the cortex at specific frequency bands during propofol-induced anaesthesia and modelling work suggests these changes result from changes in thalamocortical functional connectivity. However, it is unclear if the neurophysiological changes seen at the cortex are due to enhanced or disrupted thalamocortical communication. Direct recordings from these sites during anaesthesia that could be used to confirm such models are rare. We recorded local field potentials from the ventral intermediate nucleus of the thalamus and electrocorticography signals from the ipsilateral sensorimotor cortex in 10 patients undergoing deep brain stimulation surgery. Signals were acquired during induction of propofol anaesthesia while subjects were resting. After confirming direct structural connectivity between the thalamus and the cortical recording site, we investigated propofol-associated changes in thalamic and cortical local power as well as thalamocortical functional connectivity, as measured with coherence, debiased weighted phase lag index, and phase amplitude coupling. Propofol anaesthesia resulted in local power increases at α frequencies (8-12 Hz) across both thalamic and cortical areas. At sensorimotor cortices, there was a broadband power increase (12-100 Hz), while the power of this same broad frequency band was suppressed within the thalamus. Despite the increase in local α power both within the thalamus and cortex, thalamocortical coherence and debiased weighted phase lag index in the α/low β frequencies (8-16 Hz, which was present in the awake state) significantly decreased with propofol administration (P < 0.05, two group test of coherence). Likewise, propofol administration resulted in decreased phase amplitude coupling between the phase of α/low β in the thalamus and the amplitude of broadband gamma (50-200 Hz) in the cortex (P = 0.031, Wilcoxon signed-rank test). We also report phase amplitude coupling between the phase of slow wave oscillations (0.1-1 Hz) and amplitude of broadband frequencies (8-200 Hz) within the cortex and across thalamocortical connections, during anaesthesia, both following a peak-max pattern. While confirming α-power increases with propofol administration both in thalamus and cortex, we observed decreased thalamocortical connectivity, contradicting models that suggest increasing cortical low frequency power is necessarily related to increased thalamocortical coherence but in support of the theory that propofol-induced loss of consciousness is associated with disrupted thalamocortical communication.

The effects of different doses of dexmedetomidine on the requirements for propofol for loss of consciousness in patients monitored via the bispectral index: a double-blind, placebo-controlled trial

BACKGROUND

The α₂-adrenergic agonist dexmedetomidine (DEX) is a sedative and can be used as an adjunct to hypnotics. The study sought to evaluate the effects of different doses of DEX on the requirements for propofol for loss of consciousness (LOC) in patients monitored via the bispectral index (BIS).

METHODS

In this randomized, double-blind, three arm parallel group design and placebo-controlled trial, 73 patients aged between 18 and ~ 65 years with a BMI range of 18.0-24.5 kg·m^- 2 and an American Society of Anesthesiologists (ASA) grade I or II who were scheduled for general anesthesia at the General Hospital of Ningxia Medical University were included in this study. Anesthesiologists and patients were blinded to the syringe contents. All patients were randomly assigned in a 1:1:1 ratio to receive a 0.5 μg·kg^- 1 DEX infusion (0.5 μg·kg^- 1 DEX group; n = 24), a 1.0 μg·kg^- 1 DEX infusion (1.0 μg·kg^- 1 DEX group; n = 25) or a saline infusion (control group; n = 24) for 10 min. Propofol at a concentration of 20 mg·kg^- 1·h^- 1 was then infused at the end of the DEX or saline infusion. The propofol infusion was stopped when the patient being infused lost consciousness. The primary endpoint were propofol requirements for LOC and BIS value at LOC.

RESULTS

The data from 73 patients were analyzed. The propofol requirements for LOC was reduced in the DEX groups compared with the control group (1.12 ± 0.33 mg·kg^- 1 for the 0.5 μg·kg^- 1 DEX group vs. 1.79 ± 0.39 mg·kg^- 1 for the control group; difference, 0.68 mg·kg^- 1 [95% CI, 0.49 to 0.87]; P = 0.0001) (0.77 ± 0.27 mg·kg^- 1 for the 1.0 μg·kg^- 1 DEX group vs. 1.79 ± 0.39 mg·kg^- 1 for the control group; difference, 1.02 mg·kg^- 1 [95% CI, 0.84 to 1.21]; P = 0.0001). The propofol requirements for LOC was lower in the 1.0 μg·kg^- 1 DEX group than the 0.5 μg·kg^- 1 DEX group (0.77 ± 0.27 mg·kg^- 1 vs. 1.12 ± 0.33 mg·kg^- 1, respectively; difference, 0.34 mg·kg^- 1 [95% CI, 0.16 to 0.54]; P = 0.003). At the time of LOC, the BIS value was higher in the DEX groups than in the control group (67.5 ± 3.5 for group 0.5 μg·kg^- 1 DEX vs. 60.5 ± 3.8 for the control group; difference, 7.04 [95% CI, 4.85 to 9.23]; P = 0.0001) (68.4 ± 4.1 for group 1.0 μg·kg^- 1 DEX vs. 60.5 ± 3.8 for the control group; difference, 7.58 [95% CI, 5.41 to 9.75]; P = 0.0001).

CONCLUSION

The study showed that DEX (both 0.5 and 1.0 μg·kg^- 1 DEX) reduced the propofol requirements for LOC. DEX pre-administration increased the BIS value for LOC induced by propofol.

CLINICAL TRIAL REGISTRATION

The study was registered at ClinicalTrials.gov (trial ID: NCT02783846 on May 26, 2016).

Dynamic changes in rhythmic and arrhythmic neural signatures in the subthalamic nucleus induced by anaesthesia and tracheal intubation

BACKGROUND

Subcortical structures, including the basal ganglia, have been proposed to be crucial for arousal, consciousness, and behavioural responsiveness. How the basal ganglia contribute to the loss and recovery of consciousness during anaesthesia has, however, not yet been well characterised.

METHODS

Twelve patients with advanced Parkinson's disease, who were undergoing deep brain stimulation (DBS) electrode implantation in the subthalamic nucleus (STN), were included in this study. Local field potentials (LFPs) were recorded from the DBS electrodes and EEG was recorded from the scalp during induction of general anaesthesia (with propofol and sufentanil) and during tracheal intubation. Neural signatures of loss of consciousness and of the expected arousal during intubation were sought in the STN and EEG recordings.

RESULTS

Propofol-sufentanil anaesthesia resulted in power increases in delta, theta, and alpha frequencies, and broadband power decreases in higher frequencies in both STN and frontal cortical areas. This was accompanied by increased STN-frontal cortical coherence only in the alpha frequency band (119 [68]%; P=0.0049). We observed temporal activity changes in STN after tracheal intubation, including power increases in high-beta (22-40 Hz) frequency (98 [123]%; P=0.0064) and changes in the power-law exponent in the power spectra at lower frequencies (2-80 Hz), which were not observed in the frontal cortex. During anaesthesia, the dynamic changes in the high-gamma power in STN LFPs correlated with the power-law exponent in the power spectra at lower frequencies (2-80 Hz).

CONCLUSIONS

Apart from similar activity changes in both STN and cortex associated with anaesthesia-induced unresponsiveness, we observed specific neuronal activity changes in the STN in response to the anaesthesia and tracheal intubation. We also show that the power-law exponent in the power spectra in the STN was modulated by tracheal intubation in anaesthesia. Our results support the hypothesis that subcortical nuclei may play an important role in the loss and return of responsiveness.

Attenuation of high-frequency (30-200 Hz) thalamocortical EEG rhythms as correlate of anaesthetic action: evidence from dexmedetomidine

Background

Gamma (30-80 Hz) and high-gamma (80-200 Hz) thalamocortical EEG rhythms are involved in conscious processes and are attenuated by isoflurane and propofol. To explore the hypothesis that this attenuation is a correlate of anaesthetic action, we characterized the effect dexmedetomidine, a selective adrenergic α-2 agonist with lesser hypnotic potency, on these rhythms.

Methods

We recorded local field potentials from barrel cortex and ventroposteromedial thalamic nucleus in ten previously instrumented rats to measure spectral power (30-50 Hz, 51-75 Hz, 76-125 Hz, 126-200 Hz bands) during baseline, at four dexmedetomidine plasma concentrations obtained by i.v. target-controlled infusion (1.86, 3.75, 5.63 and 7.50 ng ml -1 ), and during recovery. Thalamocortical coherence over 0.3-200 Hz was also measured.

Results

Loss of righting reflex (LORR) occurred with 5.63 ng ml -1 . Dexmedetomidine produced a linear concentration-dependent attenuation of cortical ( P <0.04) and thalamic ( P  ≤ 0.0051) log power in all bands. Slopes for cortex and thalamus were similar. The slope for dexmedetomidine on thalamic power in the 76-200 Hz range was less than half that of the other agents ( P <0.003). LORR was associated with an increase in delta band (0.3-4.0 Hz) thalamocortical coherence ( P <0.001). Increased low-frequency coherence also occurred with propofol and isoflurane.

Conclusions

Dexmedetomidine attenuates high-frequency thalamocortical rhythms, but to a lesser degree than isoflurane and propofol. The main differences between dexmedetomidine and the other anaesthetics involved thalamic rhythms, further substantiating the link between impaired thalamic function and anaesthesia. Increased delta coherence likely reflects cyclic hyperpolarization of thalamocortical networks and may be a marker for loss of consciousness.

Propofol-induced Changes in α-β Sensorimotor Cortical Connectivity

BACKGROUND

Anesthetics are believed to alter functional connectivity across brain regions. However, network-level analyses of anesthesia, particularly in humans, are sparse. The authors hypothesized that propofol-induced loss of consciousness results in functional disconnection of human sensorimotor cortices underlying the loss of volitional motor responses.

METHODS

The authors recorded local field potentials from sensorimotor cortices in patients with Parkinson disease (N = 12) and essential tremor (N = 7) undergoing deep brain stimulation surgery, before and after propofol-induced loss of consciousness. Local spectral power and interregional connectivity (coherence and imaginary coherence) were evaluated separately across conditions for the two populations.

RESULTS

Propofol anesthesia caused power increases for frequencies between 2 and 100 Hz across the sensorimotor cortices and a shift of the dominant spectral peak in α and β frequencies toward lower frequencies (median ± SD peak frequency: 24.5 ± 2.6 Hz to 12.8 ± 2.3 Hz in Parkinson disease; 13.8 ± 2.1 Hz to 12.1 ± 1.0 Hz in essential tremor). Despite local increases in power, sensorimotor cortical coherence was suppressed with propofol in both cohorts, specifically in β frequencies (18 to 29 Hz) for Parkinson disease and α and β (10 to 48 Hz) in essential tremor.

CONCLUSIONS

The decrease in functional connectivity between sensory and motor cortices, despite an increase in local spectral power, suggests that propofol causes a functional disconnection of cortices with increases in autonomous activity within cortical regions. This pattern occurs across diseases evaluated, suggesting that these may be generalizable effects of propofol in patients with movement disorders and beyond. Sensorimotor network disruption may underlie anesthetic-induced loss of volitional control.

Oscillatory neural representations in the sensory thalamus predict neuropathic pain relief by deep brain stimulation

OBJECTIVE

Understanding the function of sensory thalamic neural activity is essential for developing and improving interventions for neuropathic pain. However, there is a lack of investigation of the relationship between sensory thalamic oscillations and pain relief in patients with neuropathic pain. This study aims to identify the oscillatory neural characteristics correlated with pain relief induced by deep brain stimulation (DBS), and develop a quantitative model to predict pain relief by integrating characteristic measures of the neural oscillations.

APPROACH

Measures of sensory thalamic local field potentials (LFPs) in thirteen patients with neuropathic pain were screened in three dimensional feature space according to the rhythm, balancing, and coupling neural behaviours, and correlated with pain relief. An integrated approach based on principal component analysis (PCA) and multiple regression analysis is proposed to integrate the multiple measures and provide a predictive model.

MAIN RESULTS

This study reveals distinct thalamic rhythms of theta, alpha, high beta and high gamma oscillations correlating with pain relief. The balancing and coupling measures between these neural oscillations were also significantly correlated with pain relief.

SIGNIFICANCE

The study enriches the series research on the function of thalamic neural oscillations in neuropathic pain and relief, and provides a quantitative approach for predicting pain relief by DBS using thalamic neural oscillations.

Attenuation of High-Frequency (50-200 Hz) Thalamocortical Electroencephalographic Rhythms by Isoflurane in Rats Is More Pronounced for the Thalamus Than for the Cortex

BACKGROUND

Thalamocortical electroencephalographic rhythms in gamma (30-80 Hz) and high-gamma (80-200 Hz) ranges have been linked to arousal and conscious processes. We have recently shown that propofol causes a concentration-dependent attenuation of the power of thalamocortical rhythms in the 50 to 200 Hz range and that this effect is far more pronounced for the thalamus. To determine whether similar attenuation occurs with other anesthetics, we characterized the concentration-effect relationship of the inhaled anesthetic isoflurane on the spectral power of these rhythms.

METHODS

Local field potentials were recorded from the barrel cortex and ventroposteromedial thalamic nucleus in 9 chronically instrumented rats to measure spectral power in the gamma/high-gamma range (30-200 Hz). Rats were placed in an airtight chamber and isoflurane was administered at 0.75%, 1.1%, and 1.5% concentrations. Spectral power was assessed during baseline, at the 3 isoflurane concentrations after 30 minutes for equilibration, and during recovery over 4 frequency bands (30-50, 51-75, 76-125, and 126-200 Hz). Unconsciousness was defined as sustained loss of righting reflex. Multiple linear regression was used to model the change in power (after logarithmic transformation) as a function of concentration and recording site. P values were corrected for multiple comparisons.

RESULTS

Unconsciousness occurred at the 1.1% concentration in all animals. Isoflurane caused a robust (P ≤ 0.008) linear concentration-dependent attenuation of cortical and thalamic power in the 30 to 200 Hz range. The concentration-effect slope for the thalamus was steeper than for the cortex in the 51 to 75 Hz (P = 0.029) and 76 to 200 Hz (P < 0.001) ranges but not for the 30 to 50 Hz range (P = 0.320). Comparison with our previously published propofol data showed that slope for cortical power was steeper with isoflurane than with propofol for all frequency bands (P = 0.033). For thalamic power, the slope differences between isoflurane and propofol were not statistically significant (0.087 ≤ P ≤ 0.599).

CONCLUSIONS

Isoflurane causes a concentration-dependent attenuation of the power of thalamocortical rhythms in the 30 to 200 Hz range, and this effect is more pronounced for the thalamus than for the cortex for frequencies >50 Hz. In comparison with propofol, isoflurane caused a greater attenuation in the cortex, but the effects on the thalamus were similar. Isoflurane and propofol cause common alterations of fast thalamocortical rhythms that may constitute an electrophysiologic signature of the anesthetized state.

Effects of Etomidate on GABAergic and Glutamatergic Transmission in Rat Thalamocortical Slices

Although accumulative evidence indicates that the thalamocortical system is an important target for general anesthetics, the underlying mechanisms of anesthetic action on thalamocortical neurotransmission are not fully understood. The aim of the study is to explore the action of etomidate on glutamatergic and GABAergic transmission in rat thalamocortical slices by using whole cell patch-clamp recording. We found that etomidate mainly prolonged the decay time of spontaneous GABAergic inhibitory postsynaptic currents (sIPSCs), without changing the frequency. Furthermore, etomidate not only prolonged the decay time of miniature inhibitory postsynaptic currents (mIPSCs) but also increased the amplitude. On the other hand, etomidate significantly decreased the frequency of spontaneous glutamatergic excitatory postsynaptic currents (sEPSCs), without altering the amplitude or decay time in the absence of bicuculline. When GABA_A receptors were blocked using bicuculline, the effects of etomidate on sEPSCs were mostly eliminated. These results suggest that etomidate enhances GABAergic transmission mainly through postsynaptic mechanism in thalamocortical neuronal network. Etomidate attenuates glutamatergic transmission predominantly through presynaptic action and requires presynaptic GABA_A receptors involvement.

Prospective Pilot Investigation: Presurgical Depressive Symptom Severity and Anesthesia Response in Women Undergoing Surgery for Gynecologic Mass Removal

BACKGROUND

Anesthesia depth has been associated with mortality. The association between anesthesia depth and presurgery physical and health status, however, is currently debated. Depression is one comorbid condition that warrants investigation given its association to reduced frontal lobe activity and high prevalence in known surgery samples (e.g., gynecologic mass removal).

PURPOSE

This pilot study examined the hypothesis that severity of acute depressive symptoms would associate with greater sensitivity to anesthesia as measured by a frontal lobe electroencephalogram (EEG)-based monitor during the anesthesia induction phase among women undergoing gynecologic mass removal.

METHOD

This was a prospective and surgery anesthesia-controlled pilot investigation with 31 women undergoing surgery for removal of pelvic/gynecologic masses. Participants completed the Millon Behavioral Medicine Diagnostic (MBMD) inventory to assess depressive-related symptomatology. A Bispectral Index Score (BIS™) monitor (Aspect Medical Systems Inc., MA) was placed on the left frontal region to measure change in response from a set pre-anesthesia baseline point throughout the induction phase (6.5 min of the anesthetic). BIS™ change was calculated using a modified "area under the curve with respect to ground" formula.

RESULTS

Greater sensitivity to anesthesia during induction was significantly associated with higher MBMD future pessimism scores and marginally associated with higher MBMD depression scores. Depressive personality, anxiety severity, tumor type, age, medication use, and comorbidity scores were not found to be predictors of BIS score change.

CONCLUSION

These pilot findings suggest that preoperative psychological health and anesthesia response are not independent. Acute presurgery depression and anesthesia response warrant closer empirical examination.

Motor System Interactions in the Beta Band Decrease during Loss of Consciousness

Communication between brain areas and how they are influenced by changes in consciousness are not fully understood. One hypothesis is that brain areas communicate via oscillatory processes, utilizing network-specific frequency bands, that can be measured with metrics that reflect between-region interactions, such as coherence and phase amplitude coupling (PAC). To evaluate this hypothesis and understand how these interactions are modulated by state changes, we analyzed electrophysiological recordings in humans at different nodes of one well-studied brain network: the basal ganglia-thalamocortical loops of the motor system during loss of consciousness induced by anesthesia. We recorded simultaneous electrocorticography over primary motor cortex (M1) with local field potentials from subcortical motor regions (either basal ganglia or thalamus) in 15 movement disorder patients during anesthesia (propofol) induction as a part of their surgery for deep brain stimulation. We observed reduced coherence and PAC between M1 and the subcortical nuclei, which was specific to the beta band (∼18-24 Hz). The fact that this pattern occurs selectively in beta underscores the importance of this frequency band in the motor system and supports the idea that oscillatory interactions at specific frequencies are related to the capacity for normal brain function and behavior.

Attenuation of high-frequency (50-200 Hz) thalamocortical EEG rhythms by propofol in rats is more pronounced for the thalamus than for the cortex

BACKGROUND

Thalamocortical EEG rhythms in gamma (30-80 Hz) and high-gamma (80-200 Hz) ranges have been linked to arousal and conscious processes. To test the hypothesis that general anesthetics attenuate these rhythms, we characterized the concentration-effect relationship of propofol on the spectral power of these rhythms. In view of the ongoing debate about cortex versus thalamus as the primary site of anesthetic action for unconsciousness, we also compared the relative sensitivity of cortex and thalamus to this effect propofol.

METHODS

Adult male Long-Evans rats were chronically implanted with electrodes in somatosensory (barrel) cortex and ventroposteromedial thalamus. Propofol was delivered by a computer-controlled infusion using real-time pharmacokinetic modeling to obtain the desired plasma concentration. Spectral power was assessed during baseline, at four stable propofol plasma-concentrations (0, 3,6,9,12 μg/ml) and during recovery over four frequency ranges (30-50, 51-75, 76-125, 126-200 Hz). Unconsciousness was defined as complete loss of righting reflex. Multiple regression was used to model the change of power (after logarithmic transformation) as a function of propofol concentration and recording site.

RESULTS

Unconsciousness occurred at the 9 μg/ml concentration in all animals. Propofol caused a robust linear concentration-dependent attenuation of cortical power in the 76-200 Hz range and of thalamic power in the 30-200 Hz range. In all instances the concentration-effect slope for the thalamus was markedly steeper than for the cortex. Furthermore the lowest concentration causing unconsciousness significantly reduced cortical power in the 126-200 Hz range and thalamic power in the 30-200 Hz range.

CONCLUSIONS

Propofol causes a concentration-dependent attenuation of the power of thalamocortical rhythms in the 30-200 Hz range and this effect is far more pronounced for the thalamus, where the attenuation provides a robust correlate of the hypnotic action of propofol [corrected].

Effects of general anesthesia with propofol on thalamocortical sensory processing in rats

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&ndash;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.