138. Is median nerve somatosensory stimulation associated to cortical changes as a function of sleep deprivation?

Sleep deprivation (SD) induces detrimental effects on alertness and cognitive performance, suggesting alterations in cortical functioning. In animals has been observed an increase in cortical excitability after SD, while results in humans are conflicting and almost exclusively limited to the motor cortex. The aim of the present study was to assess somatosensory cortical excitability after SD by means of somatosensory evoked potentials (SEPs). Sixteen healthy subjects, during 40 h of SD, participated in 4 experimental sessions (at 11.00 a.m. and 11.00 p.m. of the 1st and 2nd day) in the following sequence: (a) subjective sleepiness by means of Karolinska Sleepiness Scale (KSS) and Visual-Analog Scale for Global Vigor (VAS); (b) SEPs recordings; (c) behavioural sleepiness by means of Psychomotor Vigilance Task (PVT). SD induced an increase of subjective and behavioural sleepiness. The amplitude of different early SEPs components in S1increased as a function of time awake. Moreover, higher voltages associated with SEPs have been observed after SD in fronto-central and occipital areas. Voltage changes after SD were positively correlated with fluctuations in subjective and behavioural sleepiness. Somatosensory cortical excitability is enhanced by SD. The increase in cortical excitability seems to be at least one of the neural mechanisms underlying alterations in vigilance and cognitive performance after SD.