INTERHEMISPHERIC DIFFERENCES OF SLEEP EEG COMPLEXITY

Complexity of EEG (Omega), a global measure reflecting degree of spati al synchronization, was computed for whole night recordings of sleep E EG of 10 healthy volunteers, 9 males and 1 female (age 21-53) and 6 de pressive patients, 5 males and 1 female (age 23-64). Sleep was scored visually in 20 s epochs, Omega was calculated in 2.5 s segments and th e median from 8 segments (20 s) was calculated. Omega was calculated f or the whole field of 21 electrodes and for the left and right hemisph ere separately (2 x 8 electrodes). Measure of global power (Sigma) and generalized frequency (Phi) were also computed for the same data. In healthy subjects the complexity was higher over the right hemisphere d uring waking, and the difference shifted to higher complexity over the left hemisphere in slow wave sleep (F=5.15, df(1)=4, df(2)=6856, P < 0.0005). The opposite trend was found in depressives (F=10.51, df(1)=4 , df(2)=3960, P < 0.0001).