Patients in a vegetative state following traumatic brain injury display a reduced intracortical modulation

Patients in coma who fail to wake develop a condition known as a vegetative state (VS). While we know that some cortical activities exist in patients in VS, it remains unclear whether interneuronal modulation can be abnormal in the cerebral cortex of these patients. The aim of the study was to evaluate the inhibitory and excitatory interneuronal circuits in patients in VS following a traumatic brain injury.

Cortical excitability was studied in 5 VS patients and in 10 healthy subjects using paired pulses transcranial magnetic stimulation (TMS). Resting motor threshold and intracortical inhibition and facilitation at short intervals (2 and 10 ms, respectively) were evaluated. Two patients were studied again after their level of consciousness transitioned into a minimally conscious state (MCS).

Both intracortical inhibition and facilitation were significantly reduced in patients compared to healthy subjects (p<0.05). In addition, these results did not significantly change in the 2 patients who evolved into a MCS.

This is the first report showing an abnormal cortical excitability in patients in VS.

Our findings suggest a pathophysiological base for future work aiming to restore the lack of interneuronal transmission in patients in VS.