Rodent control of chamber brightness leads to the emergence of unique circadian rhythms

Abstract Internal circadian rhythms deviate slightly from 24 h, depending on species and individuals; thus, an environment with a 24-h light/dark cycle may not be ideal. In this study, we enabled mice to control room brightness via nose pokes and investigated subsequent biological rhythms as well as physiological and cognitive functions. The mice immediately learned the relationship between nose pokes and the resulting illuminance change and generated 24.5 ± 0.4 h-cycles in both illuminance and locomotor activity, with the illuminance phase preceding the locomotion phase. This circadian rhythm emerged during the first 3 d and was maintained for at least 30 d. Compared to mice whose light cycle was controlled by other mice (in a separate chamber) or those maintained on a regular 12 h-light/12 h-dark cycle, mice that controlled their own light cycle exhibited fewer mid-sleep awakenings, lower levels of stress-related steroids, and improved cognitive performance. These emergent circadian rhythms provide insight into the evolution of ecological circadian dynamics and may inform the development of efficient lifestyles in humans.