Single unit activities recorded in the thalamus and the overlying parietal cortex of subjects affected by disorders of consciousness

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.