CLOCK and Alzheimer disease: The precise mechanisms by which 40 Hz light therapy enhances cognitive capacity is not known; however, given 1) the role of the circadian clock in the gating of daily gamma power, 2) the reduction in gamma power in AD, and 3) the disruption in cortical/limbic circadian rhythms in AD, it is reasonable to posit that the gamma frequency therapy could be working, in part, by strengthening the circadian rhythm generating capacity of telencephalic oscillator populations.