Nocturnal Light Exposure Impairs Affective Responses in a Wavelength-Dependent Manner

Aug 9, 2013The Journal of neuroscience : the official journal of the Society for Neuroscience

Nighttime light affects emotions differently depending on its color

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Abstract

Exposure to nocturnal light at night (LAN) influences behavior and neuronal plasticity in hamsters.

Light is detected by rods, cones, and intrinsically photosensitive retinal ganglion cells (ipRGCs), which regulate circadian rhythms.
Recent findings indicate that ipRGCs project to brain regions involved in cognition and mood.
Nocturnal light exposure is associated with depressive responses and changes in neuronal structure.
Red wavelength light has limited effects on behavior and brain structure compared to shorter wavelengths.
Exposure to blue wavelengths in modern lighting conditions may disrupt mood regulation and circadian systems.

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Life on earth is entrained to a 24 h solar cycle that synchronizes circadian rhythms in physiology and behavior; light is the most potent entraining cue. In mammals, light is detected by (1) rods and cones, which mediate visual function, and (2) intrinsically photosensitive retinal ganglion cells (ipRGCs), which primarily project to the suprachiasmatic nucleus (SCN) in the hypothalamus to regulate circadian rhythms. Recent evidence, however, demonstrates that ipRGCs also project to limbic brain regions, suggesting that, through this pathway, light may have a role in cognition and mood. Therefore, it follows that unnatural exposure to light may have negative consequences for mood or behavior. Modern environmental lighting conditions have led to excessive exposure to light at night (LAN), and particularly to blue wavelength lights. We hypothesized that nocturnal light exposure (i.e., dim LAN) would induce depressive responses and alter neuronal structure in hamsters (Phodopus sungorus). If this effect is mediated by ipRGCs, which have reduced sensitivity to red wavelength light, then we predicted that red LAN would have limited effects on brain and behavior compared with shorter wavelengths. Additionally, red LAN would not induce c-Fos activation in the SCN. Our results demonstrate that exposure to LAN influences behavior and neuronal plasticity and that this effect is likely mediated by ipRGCs. Modern sources of LAN that contain blue wavelengths may be particularly disruptive to the circadian system, potentially contributing to altered mood regulation.

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Nocturnal Light Exposure Impairs Affective Responses in a Wavelength-Dependent Manner

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