These results, besides the preservation of memory performances observed after 2 h of light exposure at early night under T24, demonstrate that memory impairments observed in mice exposed to ultradian light cycle are not due to direct effects of light, contrary to the assumption of LeGates et al.18, but rather rely on non-physiologic regulation of the circadian clock, which is in accordance with human data showing that the non-circadian direct influence of light improves alertness and cognitive performances1, 32, 33. The gene discussed is CLOCK; the disease is memory impairment.