Martian Photoperiod Attenuates Waking Theta Activity at Night and Disrupts Short-term Object Memory in Mice Despite Circadian Realignment

Abstract

Aberrant light:dark cycles (T-cycles) that deviate considerably from our naturally evolved intrinsic period (τ) of ~24 h pose severe environmental challenges for the mammalian circadian system. But adaptability to T-cycles that deviate only slightly (<1 h) from T24, notably the Martian 12.33-h light:12.33-h dark cycle (T24.66) remains unexplored. By using laboratory mice, we examined the effects of T24.66 on circadian entrainment, ultradian rhythm, sleep and alertness, as well as hippocampus-mediated object memory. T24.66 lengthened τ, allowing rest–activity rhythm to realign with the slightly longer Martian photoperiod without free running. Circadian rhythmic power was not dampened under T24.66 but ultradian noise was amplified, as revealed by fast Fourier transform (FFT) and wavelet analysis. Despite circadian realignment, sleep pattern was altered with increased sleep at midnight due to an advance in the siesta peak. EEG spectral analysis revealed that waking EEG theta activity (8–12 Hz) was attenuated at night. These time-of-day dependent changes in sleep pattern and alertness were accompanied by attenuated short-term object memory at night, due to dysregulated response to familiar objects without affecting response to novelty. The T24.66 regime provides a promising approach to study the ramifications of (mal)adaptation to the Martian photoperiod for brain function.

Recommended citation: Shu Kit Eric Tam, Juntang Wang, Aleksandra Stryjska, Pascal Grange, Sze Chai Kwok. (2025). "Martian Photoperiod Attenuates Waking Theta Activity at Night and Disrupts Short-term Object Memory in Mice Despite Circadian Realignment." iScience.