Deprivation, brain topography and quantitative EEG measures during sleep.

Results obtained with a protocol of selective slow-wave sleep (SWS) deprivation, that does not affect sleep stage architecture (1), have detailed a pattern of neurophysiological changes supporting the viewof homeostatic (restorative)mechanismsduring bothREM andNREMsleep.Tonic and phasic changes have been found during recovery NREM sleep (as compared to baseline NREM sleep): a. a general increase of EEG power spectra within delta and theta frequency bands (1); b. a clear antero-posterior gradient with a further increase of spectral power on frontal areas, including also the alpha range (1); c. a greater power increase in the 1–25 Hz frequency range at C3 than C4 derivation (2); d. a decrease of sleep spindles density limited to the first sleep cycle (3); e. a reduction of ASDAarousal frequency (4) and of Cyclic Alternating Pattern (5). Although not predicted, quantitative EEG changes have been observed also during recovery REM sleep: a. an increase of delta and theta power on frontal and central derivations (1); b. a greater power increase in the 1–25 Hz frequency range at C3 than C4 derivation (2); c. a decrease in REM density, negatively correlated to the amount of SWS (3). The whole findings lead to a re-consideration of homeostatic mechanisms during REM sleep and of the functional meaning of the traditional EEG frequency bands during sleep.