In addition to environmental manipulations, physiological manipulations that affect circadian rhythmicity, such as clock gene mutations (Per1−/−: 11; Cry1−/− Cry2−/−: 49; Per2−/−: 50; Bmal1−/−: 51; 52; Clk: 51) or SCN lesions [12,53], can also elicit hippocampal-dependent memory impairments in rodents. The gene discussed is CLOCK; the disease is memory impairment.