Fig. 6.

Hierarchical multi-oscillator circadian system. a In addition to the central circadian clock in the SCN, two extra-SCN oscillators, food-entrainable oscillator (FEO) and methamphetamine-induced oscillator (MAO), are known to regulate various physiological functions, including sleep–wake rhythms. These are under the control of the SCN, but can be dissociated when food is restricted at certain hours in daytime (FEO) or methamphetamine is administered (MAO). b The SCN is composed of regional oscillators such as those in the core and shell, right and left, and anterior and posterior, each of which is comprised of multiple cellular oscillators. Regional oscillators are dissociable under specific conditions such as LD shifts, constant light, and photoperiod changes. c Peripheral clocks and behavioral rhythms are thought to be orchestrated by the SCN via neural signals (e.g., sympathetic nerves) and humoral signals (e.g., hormones and cytokines)