RecruitingDevice studyTranscranial Electrical Stimulation (TES) at Slow Oscillation (SO) Frequency During NREM SleepThe purpose of this study is to determine if the enhancement of electroencephalographic (EEG) slow-wave activity using transcranial electrical stimulation (TES) at Slow Oscillation (SO) frequency, during a restricted period of nocturnal sleep, enhances the restorative properties of that period of sleep and improves performance during a subsequent period of sleep deprivation.