Electrophysiological evidence of hemispheric asymmetry in non-REM sleep

The study presents evidence that the left (verbal) hemisphere, generally considered to be more active during the awake state, is subject to a more intense non-REM sleep. EEG, visual evoked potentials (VEP) and skin conductance response (SCR) were bilaterally recorded in 12 normal subjects during three consecutive nights. The significant results of the study (.05 rejection region) were as follows: A significant prevalence of spindles was observed over the right hemisphere while more slow activity was found over the left hemisphere. Higher amplitude of the slow secondary negative wave of the VEP substituting alpha-afteractivity in sleep was more prominent over the left hemisphere. With sleep onset higher SCR values were recorded on the left hand. In wakefulness higher SCR scores were observed on the right side of the body. Since in wakefulness the contralateral control of SCR was found to dominate, the shift towards homolateral control suggests a selective interference with the contralateral control of electrodermal activity. The results indicate that cerebral hemispheres are functionally disconnected during non-REM sleep. The implications for the analysis of sleep psychophysiology and pathology are discussed.