Exposure to light supresses the activity of the medial and superior amygdala during emotional processing

Abstract

Background: Light can influence several non-image-forming biological effects including the modulation of mood and emotional processing through neural circuitry that remains to be fully established. Rodent data showed that nuclei the amygdala, known to be important to mood regulation and emotional processing, receive direct inputs from the retina and mediate part of the affective impact of light. Here, we wanted to assess whether these animal findings translate to human beings. We determine the dynamics of the impact of light exposure on the activity of the amygdala, and whether the dynamics varied across its volume, during the processing of emotional stimulation. Methods: We used 7 Tesla functional magnetic resonance imaging to assess the impact of variations in light illuminance on the regional activity of the amygdala in healthy young adults (N = 29; 18 women; 24 +- 3.1y) during an auditory emotional task. Results: We find that several subregions of the amygdala, including the medial nucleus that receives direct retinal projection, showed a marked and linear reduction of activity with increasing illuminance when processing emotionally charged stimuli. Conclusion: We speculate that it is through the medial nucleus that light affects the emotional state of healthy individuals. These findings shed more light on the mechanisms that underlie the biological impact of light on the brain and may contribute to the benefits of light therapy in the treatment of mood disorders.