Abstract
The lack of direct neurophysiological recordings from the thalamus and the cortex hampers our understanding of vegetative state/unresponsive wakefulness syndrome and minimally conscious state in humans. We obtained microelectrode recordings from the thalami and the homolateral parietal cortex of two vegetative state/unresponsive wakefulness syndrome and one minimally conscious state patients during surgery for implantation of electrodes in both thalami for chronic deep brain stimulation. We found that activity of the thalamo-cortical networks differed among the two conditions. There were half the number of active neurons in the thalami of patients in vegetative state/unresponsive wakefulness syndrome than in minimally conscious state. Coupling of thalamic neuron discharge with EEG phases also differed in the two conditions and thalamo-cortical cross-frequency coupling was limited to the minimally conscious state patient. When consciousness is physiologically or pharmacologically reversibly suspended there is a significant increase in bursting activity of the thalamic neurons. By contrast, in the thalami of our patients in both conditions fewer than 17% of the recorded neurons showed bursting activity. This indicates that these conditions differ from physiological suspension of consciousness and that increased thalamic inhibition is not prominent. Our findings, albeit obtained in a limited number of patients, unveil the neurophysiology of these conditions at single unit resolution and might be relevant for inspiring novel therapeutic options.
Highlights
IntroductionSingle unit thalamic activity and disorders of consciousness inconsistent (MCS) behavioral evidence of awareness of self and surrounding
This is suggested by the low number of bursting neurons (BN) we found in disorders of consciousness (DOC) patients, while BN are increased in Parkinson disease in which increased inhibitory input to the thalamus has been documented [18,33]
Indications of decreased excitatory input and widespread damage come from the observation that the number of active units was lower in vegetative state/unresponsive wakefulness syndrome (VS/UWS) patients compared to minimally conscious state (MCS)
Summary
Single unit thalamic activity and disorders of consciousness inconsistent (MCS) behavioral evidence of awareness of self and surrounding Unconsciousness in these patients is correlated with decreased positive connectivity within the default mode network and abnormally increased positive connectivity between this and the task-positive network [3], while the activities of these two networks are anticorrelated in normal subjects [4]. These changes in functional connectivity are not exclusively generated by cortical damage and reflect changes in the activity of the thalamus and basal ganglia [5,6]. Thalamic damage followed by atrophy is usually more extensive in trauma patients [8]
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