Fig. 3

The SCN regulates behavioral circadian rhythms. a The SCN in a coronal section (50-μm thickness) of the hypothalamus stained by neutral red. The scale bar indicates 200 μm. A pair of nuclei with densely packed neurons is apparent in the middle base of the brain. b A male mouse on a running wheel. c A representative actogram of wheel-running activity in an SCN-lesioned mouse under an LD cycle. The nocturnal (night-active) rhythm has disappeared except for an ultradian rhythm, with a period of 2–4 h. Light condition is indicated at the top of the figure; the open bar is a light phase, and the closed bar is dark