SLEEP DEPRIVATION AND CORTICAL EXCITABILITY INTRODUCTION SLEEP AND EPILEPSY ARE INTIMATELY RELATED AND INFLUENCE EACH OTHER.1 FOR EXAMPLE, FLUCTUA- TIONS OF ALERTNESS INDUCE QUALITATIVE AND quan-

SLEEP AND EPILEPSY ARE INTIMATELY RELATED AND INFLUENCE EACH OTHER.1 FOR EXAMPLE, FLUCTUATIONS OF ALERTNESS INDUCE QUALITATIVE AND quantitative changes of EEG epileptiform abnormalities. Conversely, epileptic activity may alter sleep architecture.2 In particular, sleep deprivation (SD) is capable of influencing ictal/interictal epileptic activities.3 SD may induce seizures in patients with epilepsy and may activate focal and, particularly, generalized interictal epileptiform discharges in almost 50% of epileptic patients.4 SD is therefore used in clinical settings as an activating procedure of EEG in the diagnosis of epilepsy.5 The mechanisms underlying such phenomena are controversial.6-9 Two main hypotheses have been suggested: a) the induced activation of epileptic phenomena is a direct consequence of SD, so that it is “per se” capable of promoting an increased cortical excitability10; b) the induced epilepsy is mediated by vigilance modification as drowsiness following SD, often documented in the EEG recordings.11 A few studies concerning the mutual influences of cortical excitability, interictal epileptiform abnormalities, and sleep/wake rhythm have been reported.12-14 Transcranial magnetic stimulation (TMS) is a safe and noninvasive diagnostic technique for the study of the motor pathways in healthy and diseased humans.15,16 Standard TMS measures, such as excitability threshold and amplitude of motor evoked potential, are very sensitive for detecting both physiological and pathological conditions involving central motor pathways. In addition, more complex TMS protocols, such as paired-pulse TMS and silent period, allow the documentation of motor intracortical inhibition.11 The aim of our study was to use TMS in order to explore the effects of total SD upon the balanced excitatory/inhibitory properties of the brain in healthy subjects.