Increasing cortical excitability: A possible explanation for the proconvulsant role of sleep deprivation

Study Objective: Sleep deprivation (SD) is known to facilitate both seizures and interictal epileptiform abnormalities. For this reason, it is often used in the routine diagnostic workup of epileptic patients as an activating procedure for eliciting epileptiform and/or seizure patterns in their EEGs. In order to evaluate the effects of SD on cortical excitability, we studied the effects of sleep loss on healthy subjects by transcranial magnetic stimulation (TMS). Design and Participants: Seven normal subjects underwent TMS examination in baseline condition and after total sleep deprivation. The TMS investigation included two protocols: a) the evaluation of motor evoked potential and silent period parameters recorded in response to single-pulse magnetic stimulation; and b) the evaluation of the time course of intracortical motor activity tested with paired-pulse TMS applied at inter-stimulus intervals of 1-6 ms. Setting: Clinical neurophysiology laboratory in a general hospital. Interventions: None Results: After SD, the principal finding observed using single-pulse TMS was a decrease of the silent period duration, whereas a reduction of the intracortical inhibition, in particular at inter-stimulus intervals 1 and 2 ms, was found, using the paired-pulse TMS. Conclusion: Our findings suggest that SID may modify cortical excitability, seen as the balance between inhibitory and excitatory cortical phenomena, which could reduce the epileptic threshold.