Brain responsiveness to non-painful tactile stimulation during sleep

Aim: Electrophysiological responses evoked in the brain in response to non painful tactile stimuli were examined as evoked potentials during sleep.Method: First night sleep recordings of 11 volunteers (age range : 21-24, mean age: 22,55 ± 1,21; 6 male) were examined in the study. Uniform non painful tactile pressure stimulation was applied to two fingers (fore and middle fingers) of the left and right hand by means pneumatic stimulator. Electroencephalography was recorded from 40 channels throughout the night. Sleep stages were determined according to the sleep scoring system; somatosensory evoked potentials, and somatosensory event related potentials corresponding to each sleep stage was examined.Results: As sleep deepened an increase was observed in amplitude and latency of the N300, N_late negative components and the P450 positive component. P900 late positive component latency was found to be later in light sleep compared to deep sleep. The amplitude of responses in frontal areas was observed to be greater than those in the occipital and parietal regions.Conclusion: Response to somatosensory evoked potential and somatosensory event related potential stimuli were observed to be generalized throughout the cortex. Furthermore in our study which employed non painful tactile stimulation, the latency and amplitude of somatosensory evoked potentials were found to differ in various sleep stages.Key Words: Sleep, Electrophysiology, Somatosensory Evoked Potentials, somatosensory event related potential