Reduced intra-cortical inhibition after sleep deprivation: a transcranial magnetic stimulation study.

Sleep deprivation has multiple effects on brain function. It increases the risk for epileptic seizures both in healthy individuals and in patients with epilepsy. Furthermore it represents an effective antidepressive intervention with rapid onset. However, the mechanisms underlying these effects are still largely unknown. Transcranial magnetic stimulation (TMS) can be used as a non-invasive method for the measurement of motor cortex excitability. Here we used TMS for assessing sleep deprivation effects on cortical excitability in healthy individuals. Before and after 24 h of sleep deprivation, parameters of cortical excitability (resting motor threshold, short intracortical inhibition, intracortical facilitation, cortical silent period) were measured in a sample of 15 healthy volunteers (11 women, 4 men, aged between 21 and 30 years with a mean of 24.3±2.7 years). We detected a significant (p=0.042) reduction of short intracortical inhibition (SICI) after sleep deprivation. Motor threshold, intracortical facilitation and contralateral silent period remained unchanged. Our results confirm previous studies which have demonstrated changes of SICI after sleep deprivation. Our findings further suggest that the increased risk for epileptic seizures after sleep deprivation is mediated by a reduction of intracortical inhibition. Whether this mechanism is also involved in mediating the antidepressant effect of sleep deprivation has to be addressed by further studies in depressive patients.