Changes of cortical excitability due to steep deprivation: A transcranial magnetic stimulation study

Objective Sleep deprivation activates EEG epileptic discharges in an unknown way. Transcranial magnetic stimulation (TMS) can give information on the excitability status of the primary motor cortex, including the balance between inhibitory and facilitatory phenomena. Methods We studied seven healthy subjects (four men and four women). TMS (single and paired) was performed by a focal coil over the primary motor cortex, at the "hot spot" for the right first dorsal interosseous muscle (FDD. We measured the following motor evoked potential (MEP) features: (a) active and resting threshold to stimulation; (b) duration of the central silent period; (c) amount of inhibition on paired TMS at the interstimulus intervals (ISIs) 2 and 3 ms; amount of facilitation at ISIs 14 and 16 ms. We recorded 8 conditioned and 8 control responses at each ISI. The amplitude of the conditioned MEP was expressed as percent of control. The whole TMS session was repeated after sleep deprivation of at least 24 hours. Statistical evaluation was based on a repeated measures ANOVA model with post hoc Bonferroni tests. Results After sleep deprivation, the threshold to stimulation (in the active and resting muscle), as well as the silent period did not change significantly. On the contrary, the paired stimulus study showed significant (/><0.05) reduction in both cortico-cortical inhibition and facilitation. Conclusions TMS disclosed that sleep deprivation was associated with changes in the inhibition-facilitation balance in primary motor cortex. These may represent one background factor favouring the appearance of EEG epileptic discharges.