Figure 1: Schematic diagram of the impact of ancestral versus modern day light exposure and social constraints on sleep patterns. | Scientific Reports

Figure 1: Schematic diagram of the impact of ancestral versus modern day light exposure and social constraints on sleep patterns.

From: The effects of self-selected light-dark cycles and social constraints on human sleep and circadian timing: a modeling approach

Figure 1

(a) Light input into the circadian pacemaker representative of hunter/gatherers in black and humans in industrialised societies in red. In both conditions the light input depicted is gated by the sleep-wake cycle, i.e. light input occurs during wake but not during sleep. By switching on electric light modern humans can extend the light period. (b) Core processes that govern wake/sleep timing are the circadian wake/sleep propensity rhythm and the sleep homeostat. Under normal conditions, circadian wake propensity (C-WP) is high during the day (wakefulness) and low during the night (sleep). Homeostatic sleep propensity (H-SP) increases during wakefulness and dissipates during sleep. The C-WP and the H-WP are shown in the absence/presence of evening light in black/red respectively. (c) Evening light exposure delays the timing of sleep onset and the circadian rhythm, but social constraints, indicated by the alarm clock, force us to wake up early. In the absence of social contraints, indicated by the crossed out alarm clock, we wake up later, in phase with the delayed circadian clock. Overall the self-selection of light leads to a delayed and irregular sleep pattern. Sleep timing is shown in the absence/presence of evening light in black/red respectively.

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