Connettivita’ funzionale fronto-posteriore durante l’addormentamento.

The aim of this study was to assess the functional coupling between anterior and posterior areas as induced by the sleep onset (SO) process. The cortico-cortical functional coupling was indexed by the directed transfer function (DTF), an advanced computational analysis of EEG data which provides an estimation of the direction of the information flow. Since it has been reported that more anterior areas first synchronize sleep EEG activity, we hypothesized a antero-posterior (A-P) direction of the cortical functional coupling during the SO, and that this change in the direction of information flow should be enhanced by a Slow-Wave Sleep (SWS) deprivation. Methods. Ten normal male students slept for six consecutive nights (1: adaptation, 2: baseline, 3: baseline with awakenings, 4-5: SWS deprivations, 6: recovery), with standard polysomnographic recordings. The DTF was computed on data recorded during nights 2 and 6 from anterior (FzA1) and posterior (PzA1, OzA1) derivations. Results. During the baseline night, the presleep period was characterized by posterior-anterior functional cortical coupling, while at SO there was an inversion of that direction, confirming the notion that anterior cortical areas first synchronize sleep EEG activity. During the recovery night following SWS deprivation, the anterior-to-posterior direction of functional cortical coupling was already present in the presleep period, indicating that SWS deprivation advances the shift to an A-P directionality of functional cortical coupling, possibly as a consequence of heightened sleep pressure. Conclusions. These findings support the notion of sleep as a local process, showing that the SO process is sub-served by the functional coordination of a cortical fronto-posterior network and that a spread of synchronizing signals from associative prefrontal to posterior areas plays a role in the wake-sleep transition.