Despite decades of study, no ironclad conclusion has been reached concerning the biological function of sleep in humans. Recent theories have proposed that sleep might play a role in maintaining cortical excitability at safe levels by downregulating excessive intersynaptic connections accumulated during a waking episode. In line with this theory, sleep deprivation has been shown to increase cortical excitability in studies using transcranial magnetic stimulation (TMS) and electroencephalography (EEG). In this pilot study (N=4) we used magnetoencephalography (MEG) to study the effects of 24 hours of sleep deprivation on somatosensory evoked fields (SEFs). Sleep deprivation increased the amplitude of primary somatosensory P35m component by 36%. Our preliminary findings confirm and delineate the previous EEG findings of enhanced somatosensory activation after sleep deprivation, thus indicating increased cortical excitability following sleep loss.