Cortical excitability and sleep deprivation: a transcranial magnetic stimulation study

The objective was to assess the changes in cortical excitability after slee p deprivation in normal subjects. Sleep deprivation activates EEG epileptif orm activity in an unknown way. Transcranial magnetic stimulation (TMS) can inform on the excitability of the primary motor cortex. Eight healthy subj ects (four men and four women) were studied. Transcranial magnetic stimulat ion (single and paired) was performed by a focal coil over the primary moto r cortex, at the "hot spot" for the right first dorsal interosseous muscle. The following motor evoked potential features were measured: (a) active an d resting threshold to stimulation; (b) duration of the silent period; (c) amount of intracortical inhibition on paired TMS at the interstimulus inter vals of 2 and 3 ms and amount of facilitation at interstimulus intervals of 14 and 16 ins. The whole TMS session was repeated after a sleep deprivatio n of at least 24 hours. After the sleep deprivation, the threshold to stimu lation (in the active and resting muscle), as well as the silent period, di d not change significantly. By contrast, the paired stimulus study showed a significant (p <0.05) reduction in both intracortical inhibition and facil itation. Thus, TMS showed that sleep deprivation is associated with changes in inhibition-facilitation balance in the primary motor cortex of normal s ubjects. These changes might have a link with the background factors of the "activating" effects of sleep deprivation.