Antero-posterior EEG changes during the wakefulness-sleep transition.
OBJECTIVE
To investigate the brain topography of the human sleep EEG along the antero-posterior axis during the wakefulness-sleep transition, by means of both a single Hz analysis and a grouped-frequency analysis of EEG changes.


METHODS
EEG power values were calculated across a 1-28 Hz frequency range in a 1 Hz resolution during the wakefulness-sleep transition of 7 normal subjects. Topographical changes were assessed from C3-A2, C4-A1, Fpz-A1, Fz-A1, Cz-A1, Pz-A1, Oz-A1 recordings, after averaging individual time series, aligned with respect to the onset of stage 2.


RESULTS
The single Hz analysis showed that before sleep onset (SO), the <7 Hz slow frequencies were more prominent at the more anterior scalp locations; this anterior prominence was counterbalanced by a reciprocal prevalence across the >8 Hz frequencies of EEG activity from the occipital areas; while the >13 Hz fast frequencies were not characterized by significant antero-posterior differences. After SO, more EEG power was found in the range of slow frequencies at the centro-frontal scalp locations and a second peak of EEG activity was also revealed within the range of the sigma frequency, higher at the centro-parietal scalp locations. No consistent topographical changes were observed within the range of faster EEG frequencies. Grouped-frequency analysis confirmed these results, also pointing to different changes in the alpha frequency as a function of the SO point.


CONCLUSIONS
The results suggest that: (a) the alpha rhythm spreads anteriorly as the transition progresses; (b) several anterior areas first synchronize EEG activity; (c) the functional meaning of the EEG bands during the SO period should be partially revised with regard at least to alpha rhythm; (d) SO coincides with the start of stage 2.
De Gennaro
L
L
Dipartimento di Psicologia, Sezione di Neuoroscienze, Università degli Studi di Roma La Sapienza, Via dei Marsi, 78, 00185, Rome, Italy. luigi.degennaro@uniroma1.it
Ferrara
M
M
Curcio
G
G
Cristiani
R
R
D000328:Adult; D000704:Analysis of Variance; D001921:Brain / Q000502:physiology*; D004569:Electroencephalography; D007839:Functional Laterality; D006801:Humans; D008297:Male; D015999:Multivariate Analysis; D017286:Polysomnography; D012016:Reference Values; D012535:Scalp / Q000502:physiology; D012890:Sleep / Q000502:physiology*; D012894:Sleep Stages / Q000502:physiology*; D013997:Time Factors; D014851:Wakefulness / Q000502:physiology*