second analysis evaluated the circadian modulation of PVT brain responses using an empirical marker of the circadian process: the mean melatonin levels across volunteers (Fig. 3A, red). We simultaneously assessed whether brain responses to the PVT were modulated by accumulating sleep pressure (blue) and how circadian rhythm and homeostatic sleep pressure interact (green). Because no pure marker of homeostatic sleep pressure can be derived from empirical data obtained during sleep deprivation, its effect was modelled as monotonically decreasing with elapsed time awake and increasing after recovery sleep (Supplementary materials), as empirically observed (14) and usually modelled (15). A Fig. 3.PVT fMRI analysis 2. Illustration of dimensionless fixed-effects fMRI contrasts testing (1) a decrease in response with increasing sleep pressure during wakefulness and its recovery after sleep (blue), (2) their fluctuation in association with mean melatonin level (red) and the interaction between these two factors (green). Note that the interaction is characterized by a steady level of response up to the evening sessions of day 3. Middle column: significant effects of homeostatic sleep pressure (blue), circadian (red) and their interaction (green), displayed at pFamily Wise Error (FWE) whole brain<0.05 over an individual normalized T1-weighted MR scan. Left- and right-hand side columns provide two different representations of the time course of brain responses which were significant for sleep debt (blue border), circadian (red border) or the interaction (green border) contrasts. Irrespective of the contrast, beta estimates are plotted against clock time (left-hand panels, linear regression is computed with respect to time awake during the SD period) and time relative to DLMO (right-hand panels; mean melatonin levels in grey; activity estimates have been interpolated every 2h24min from -12h to +28h). Coordinates expressed in mm along z axis. NS: non-significant. This second analysis indicated that the time course of responses significantly correlated with mean melatonin levels in a number of subcortical areas (midbrain, cerebellum, basal ganglia,
second analysis evaluated the circadian modulation of PVT brain responses using an empirical marker of the circadian process: the mean melatonin levels across volunteers (Fig. 3A, red). We simultaneously assessed whether brain responses to the PVT were modulated by accumulating sleep pressure (blue) and how circadian rhythm and homeostatic sleep pressure interact (green). Because no pure marker of homeostatic sleep pressure can be derived from empirical data obtained during sleep deprivation, its effect was modelled as monotonically decreasing with elapsed time awake and increasing after recovery sleep (Supplementary materials), as empirically observed (14) and usually modelled (15). A Fig. 3.PVT fMRI analysis 2. Illustration of dimensionless fixed-effects fMRI contrasts testing (1) a decrease in response with increasing sleep pressure during wakefulness and its recovery after sleep (blue), (2) their fluctuation in association with mean melatonin level (red) and the interaction between these two factors (green). Note that the interaction is characterized by a steady level of response up to the evening sessions of day 3. Middle column: significant effects of homeostatic sleep pressure (blue), circadian (red) and their interaction (green), displayed at pFamily Wise Error (FWE) whole brain<0.05 over an individual normalized T1-weighted MR scan. Left- and right-hand side columns provide two different representations of the time course of brain responses which were significant for sleep debt (blue border), circadian (red border) or the interaction (green border) contrasts. Irrespective of the contrast, beta estimates are plotted against clock time (left-hand panels, linear regression is computed with respect to time awake during the SD period) and time relative to DLMO (right-hand panels; mean melatonin levels in grey; activity estimates have been interpolated every 2h24min from -12h to +28h). Coordinates expressed in mm along z axis. NS: non-significant. This second analysis indicated that the time course of responses significantly correlated with mean melatonin levels in a number of subcortical areas (midbrain, cerebellum, basal ganglia,
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