Regional differences of the human sleep EEG in response to selective slow-wave sleep deprivation.

Objectives: Recent evidence suggests that the human sleep electroencephalogram (EEG) shows regional differences over both the sagittal and coronal planes. In the present study we investigated the presence of antero-posterior and interhemispheric differences in the homeostatic regulation of human sleep EEG power, during selective slow-wave sleep (SWS) deprivation and the ensuing recovery sleep. Methods: After one adaptation and two baseline nights, 10 normal male subjects underwent two consecutive nights of selective SWS deprivation, accomplished by means of an acoustic stimulation technique. A recovery night then followed. EEG power spectra of seven derivations (C3-A2, C4-A1, Fpz-A1, Fz-A1, Cz-A1, Pz-A1, Oz-A1) were computed by a Fast Fourier Transform routine in the 1–25 Hz range, separately for NREM (stage 2+3+4) and REM sleep. Results: During the SWS deprivation nights, larger decreases of EEG power were found over the right central, frontopolar, central and parietal derivations, encompassing the delta, theta and alpha range, while only the slow-delta range (1–2 Hz) was affected at the frontal and left central derivations. Recovery sleep was characterized, at least at the more anterior derivations, by a generalized increase of power during NREM sleep encompassing the delta, theta and alpha bands. A clear anterio-posterior gradient of EEG power increases was found, the frontal derivation showing the largest rebound effect. As regards the interhemispheric differences in response to SWS deprivation, only the left central derivation (C3) showed an increase of EEG power in the delta–theta range during NREM sleep of the recovery night. Modifications of EEG power during REM sleep were also found. During the SWS deprivation nights there was an increase of EEG power in the entire 1–25 Hz frequency range, in particular at C3 and Cz, while recovery sleep was characterized by an increase of EEG power in the delta–theta frequency range at Fz, Cz and C3 derivations. The !resistance" to selective SWS deprivation of the frontal and left central derivations, together with their larger increases of EEG power during recovery sleep, may be interpreted as an index of higher sleep need of both the frontal cortical areas and the left hemisphere, further confirming that some aspects of the regulatory processes of human sleep are local in nature and that the human sleep EEG shows usedependent characteristics. Conclusions: EEG power is characterized by antero-posterior and hemispheric asymmetries during SWS deprivation and the following recovery night.