Aberrant Light Schedules Could Directly Impair Mood, Learning

In experimental study, impairment occurs despite no effect on sleep and circadian rhythms

THURSDAY, Nov. 15 (HealthDay News) -- Mice exposed to aberrant light schedules show impaired mood and learning, even though their sleep and circadian rhythms are unaffected, according to a study published online Nov. 14 in Nature.

To investigate whether irregular light schedules directly affect mood and cognitive functions, Tara A. LeGates, from Johns Hopkins University in Baltimore, and colleagues subjected mice to an aberrant cycle of 3.5 hours of light and 3.5 hours of darkness.

The researchers found that, while the aberrant light cycle did not affect sleep architecture, sleep amounts, or circadian rhythms, the mice displayed increased depression-like behaviors and impaired learning and hippocampal long-term potentiation. Antidepressants such as fluoxetine or desipramine restored learning. Mice lacking intrinsically photosensitive retinal ganglion cells, which signal light information for non-image-forming visual functions, did not have impaired mood and learning after exposure to the aberrant light cycle.

"These findings demonstrate the ability of light to influence cognitive and mood functions directly through intrinsically photosensitive retinal ganglion cells," LeGates and colleagues conclude.

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