Pre-clinical work suggests that the amygdala is one of the primary brain areas which may underpin the direct effects of light on mood.
Light therapy is an effective, rapidly acting intervention for depressive disorders, including major depression and seasonal affective disorder. In humans, light exposure improves mood and alters function in brain areas that are important for cognition. Light acutely enhances fear-related learning, and the retina-amygdala pathway is involved in light-related alterations in both mood and learning. This circuitry is critical for the regulation of negative affect. The amygdala, and connections between the ventro-medial prefrontal cortex (vmPFC) and amygdala, play a role in regulating fear-related responses. In rodents, ipRGCs directly innervate the amygdala, a neural structure that is central to the regulation of emotion. These effects are likely to be largely driven by intrinsically photosensitive retinal ganglion cells (ipRGCs) containing the photopigment melanopsin, which project to many subcortical brain regions. Non-visual effects of light include the regulation of the circadian clock, alertness, physiological arousal, and mood. This does not alter our adherence to PLOS ONE policies on sharing data and materials.īeyond vision, light has powerful effects on brain function and human health. SWC has additionally consulted for Versalux and Dyson. AJKP and SWC are both investigators on projects funded by the Alertness Safety and Productivity CRC, have received research funds from Versalux and Delos, and, consulted for Beacon. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Ĭompeting interests: EMM, GRP & SDJ declare no relevant conflicts. SDJ is supported by an Australian National Health and Medical Research Council Fellowship (APP1174164). GRP is supported by an ACURF Program Grant. įunding: This work was funded by a Turner Institute Strategic Project Grant awarded to SWC, SDJ, EMM and AJKP and a Medicine Nursing and Health Sciences Platform Access Grant awarded to SWC and GRP. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.ĭata Availability: The first-level model outputs and scripts supporting our findings are available at. Received: JanuAccepted: Published: June 16, 2021Ĭopyright: © 2021 McGlashan et al. Badea, National Eye Centre, UNITED STATES These effects may contribute to light’s mood-elevating effects, via a reduction in negative, fear-related affect and enhanced processing of negative emotion.Ĭitation: McGlashan EM, Poudel GR, Jamadar SD, Phillips AJK, Cain SW (2021) Afraid of the dark: Light acutely suppresses activity in the human amygdala. Furthermore, functional connectivity between the amygdala and ventro-medial prefrontal cortex was enhanced during light relative to dark. Moderate light exposure resulted in greater suppression of amygdala activity than dim light. Light, compared with dark, suppressed activity in the amygdala. Participants were exposed to alternating 30s blocks of light (10 lux or 100 lux) and dark (<1 lux), with each light intensity being presented separately.
We examined the effect of passive dim-to-moderate white light exposure on activation of the amygdala in healthy young adults using the BOLD fMRI response (3T Siemens scanner n = 23). However, the effect of light on activity in the amygdala in humans is not well understood.
A direct effect of light on the amygdala represents a plausible mechanism of action for light’s mood-elevating effects in humans. In rodents the amygdala receives direct light input from the retina, and light may play a role in fear-related learning. The amygdala plays a critical role in regulating emotion, including fear-related responses.