Sequential reinstatement of neocortical activity during slow oscillations depends on cells’ global activity
Résumé
During Slow Wave Sleep (SWS), cortical activity is dominated by endogenous processes
modulated by slow oscillations (0.1–1 Hz): cell ensembles fl uctuate between states of sustained
activity (UP states) and silent epochs (DOWN states). We investigate here the temporal
structure of ensemble activity during UP states by means of multiple single unit recordings in
the prefrontal cortex of naturally sleeping rats. As previously shown, the fi ring rate of each PFC
cell peaks at a distinct time lag after the DOWN/UP transition in a consistent order. We show
here that, conversely, the latency of the fi rst spike after the UP state onset depends primarily
on the session-averaged fi ring rates of cells (which can be considered as an indirect measure
of their intrinsic excitability). This latency can be explained by a simple homogeneous process
(Poisson model) of cell fi ring, with sleep averaged fi ring rates employed as parameters. Thus,
at DOWN/UP transitions, neurons are affected both by a slow process, possibly originating in
the cortical network, modulating the time course of fi ring for each cell, and by a fast, relatively
stereotyped reinstatement of activity, related mostly to global activity levels.