R D Sanders1, M I Banks2, M Darracq2, R Moran3, J Sleigh4, O Gosseries5, V Bonhomme6, J F Brichant7, M Rosanova8, A Raz9, G Tononi10, M Massimini8, S Laureys11, M Boly12. 1. Department of Anesthesiology, University of Wisconsin, Madison, WI, USA. Electronic address: robert.sanders@wisc.edu. 2. Department of Anesthesiology, University of Wisconsin, Madison, WI, USA. 3. Faculty of Engineering, University of Bristol, Bristol, UK. 4. Department of Anaesthesia, Waikato Hospital, Hamilton, New Zealand. 5. Coma Science Group, GIGA-consciousness, University of Liège, Liège, Belgium. 6. Anesthesia and Intensive Care Laboratory, GIGA-Consciousness, University of Liège, Liège, Belgium; Department of Anestheisa and ICM, CHU Liège, Liège, Belgium; University Department of Anesthesia and ICM, CHR Citadelle, Liège, Belgium. 7. Department of Anestheisa and ICM, CHU Liège, Liège, Belgium. 8. Department of Biomedical and Clinical Sciences, University of Milan, Milan, Italy. 9. Department of Anesthesiology, University of Wisconsin, Madison, WI, USA; Rambam Healthcare Campus, Haifa, Israel. 10. Department of Psychiatry, University of Wisconsin, Madison, WI, USA. 11. Coma Science Group, GIGA-consciousness, University of Liège, Liège, Belgium; Department of Neurology, CHU Liège, Liège, Belgium. 12. Department of Psychiatry, University of Wisconsin, Madison, WI, USA; Department of Neurology, University of Wisconsin, Madison, WI, USA.
Abstract
BACKGROUND: Impaired consciousness has been associated with impaired cortical signal propagation after transcranial magnetic stimulation (TMS). We hypothesised that the reduced current propagation under propofol-induced unresponsiveness is associated with changes in both feedforward and feedback connectivity across the cortical hierarchy. METHODS: Eight subjects underwent left occipital TMS coupled with high-density EEG recordings during wakefulness and propofol-induced unconsciousness. Spectral analysis was applied to responses recorded from sensors overlying six hierarchical cortical sources involved in visual processing. Dynamic causal modelling (DCM) of induced time-frequency responses and evoked response potentials were used to investigate propofol's effects on connectivity between regions. RESULTS: Sensor space analysis demonstrated that propofol reduced both induced and evoked power after TMS in occipital, parietal, and frontal electrodes. Bayesian model selection supported a DCM with hierarchical feedforward and feedback connections. DCM of induced EEG responses revealed that the primary effect of propofol was impaired feedforward responses in cross-frequency theta/alpha-gamma coupling and within frequency theta coupling (F contrast, family-wise error corrected P<0.05). An exploratory analysis (thresholded at uncorrected P<0.001) also suggested that propofol impaired feedforward and feedback beta band coupling. Post hoc analyses showed impairments in all feedforward connections and one feedback connection from parietal to occipital cortex. DCM of the evoked response potential showed impaired feedforward connectivity between left-sided occipital and parietal cortex (T contrast P=0.004, Bonferroni corrected). CONCLUSIONS: Propofol-induced loss of consciousness is associated with impaired hierarchical feedforward connectivity assessed by EEG after occipital TMS.
BACKGROUND: Impaired consciousness has been associated with impaired cortical signal propagation after transcranial magnetic stimulation (TMS). We hypothesised that the reduced current propagation under propofol-induced unresponsiveness is associated with changes in both feedforward and feedback connectivity across the cortical hierarchy. METHODS: Eight subjects underwent left occipital TMS coupled with high-density EEG recordings during wakefulness and propofol-induced unconsciousness. Spectral analysis was applied to responses recorded from sensors overlying six hierarchical cortical sources involved in visual processing. Dynamic causal modelling (DCM) of induced time-frequency responses and evoked response potentials were used to investigate propofol's effects on connectivity between regions. RESULTS: Sensor space analysis demonstrated that propofol reduced both induced and evoked power after TMS in occipital, parietal, and frontal electrodes. Bayesian model selection supported a DCM with hierarchical feedforward and feedback connections. DCM of induced EEG responses revealed that the primary effect of propofol was impaired feedforward responses in cross-frequency theta/alpha-gamma coupling and within frequency theta coupling (F contrast, family-wise error corrected P<0.05). An exploratory analysis (thresholded at uncorrected P<0.001) also suggested that propofol impaired feedforward and feedback beta band coupling. Post hoc analyses showed impairments in all feedforward connections and one feedback connection from parietal to occipital cortex. DCM of the evoked response potential showed impaired feedforward connectivity between left-sided occipital and parietal cortex (T contrast P=0.004, Bonferroni corrected). CONCLUSIONS:Propofol-induced loss of consciousness is associated with impaired hierarchical feedforward connectivity assessed by EEG after occipital TMS.
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