Dynamics of the EEG slow-wave synchronization during sleep.
OBJECTIVE
To study the dynamics of spatial synchronization of the slow-wave activity recorded from different scalp electrodes during sleep in healthy normal controls.


METHODS
We characterized the different levels of EEG synchronization during sleep (in the 0.25-2.5 Hz band) of five healthy subjects by means of the synchronization likelihood (SL) algorithm and analyzed its long-range temporal correlations by means of the detrended fluctuation analysis (DFA).


RESULTS
We found higher levels of interregional synchronization during 'cyclic alternating pattern' (CAP) sleep than during nonCAP with a small but significant difference between its A and B phases. SL during CAP showed fluctuations probably corresponding to the single EEG slow-wave elements. DFA showed the presence of two linear scaling regions in the double-logarithmic plot of the fluctuations of SL level as a function of time scale. This indicates the presence of a characteristic time scale in the underlying dynamics which was very stable among the different subjects (1.23-1.33 s). We also computed the DFA exponent of the two scaling regions; the first, with values approximately 1.5, corresponded to fluctuations with period 0.09-0.75 s and the second, with values approximately 1, corresponded to fluctuations with period 1.5-24.0 s. Only the first exponent showed different values during the different sleep stages.


CONCLUSIONS
All these results indicate a different role for each sleep stage and CAP condition in the EEG synchronization processes of sleep which show a complex time structure correlated with its neurophysiological mechanisms.


CONCLUSIONS
Very slow oscillations in spatial EEG synchronization might play a critical role in the long-range temporal EEG correlations during sleep which might be the chain of events responsible for the maintenance and correct complex development of sleep structure during the night.
Ferri
Raffaele
R
Department of Neurology I.C., Oasi Institute (IRCCS), Sleep Research Centre, Troina, Italy. rferri@oasi.en.it
Rundo
Francesco
F
Bruni
Oliviero
O
Terzano
Mario G
MG
Stam
Cornelis J
CJ
D000328:Adult; D003344:Cortical Synchronization; D005260:Female; D006801:Humans; D008297:Male; D008959:Models, Neurological; D010507:Periodicity; D017286:Polysomnography; D012890:Sleep / Q000502:physiology*; D012895:Sleep, REM / Q000502:physiology*