Build-up of delta activity within NREM sleep episodes. Data correspond to mean (± SEM) of normalized delta activity of 18 animals under BL and FR (cyan and reddish symbols respectively) obtained at one 15-s epoch time resolution. The first unequivocal NREM sleep epoch of the episode was considered zero level. Data were analyzed within 6 blocks defined for its biological significance: ZT 0–1, before Food Anticipatory Interval; ZT 2–4, Food Anticipatory Interval; ZT 5–8, food availability window; ZT 9-11, from end of food availability window to lights-off; ZT 12–17, first half of dark phase; and ZT 18–23, second half of dark phase. Up and down arrowheads indicate higher or lower values respect to BL (paired t-test comparisons, P < 0.05, after 2-way rmANOVA for factors epoch and protocol within each block).