Effects of light therapy on amygdala connectivity and serotoninergic system in young adults with subthreshold depression

Motivation: Bright light therapy (BLT) is effective for subthreshold depression (StD), with the amygdala playing a key role. Goal(s): To assess BLT's impact on amygdala subregion functional connectivity (FC) and its link to monoaminergic activity. Approach: StD were divided into BLT and placebo groups, undergoing MRI before and after 8 weeks. Both static and dynamic FC analyses of the amygdala and subfields were conducted. Results: BLT reduced Hamilton Depression Rating Scale (HAM-D) scores and altered amygdala FC with thalamus, frontal lobe, and middle temporal gyrus (MTG) in StD. Baseline amygdala FC predicted post-BLT HAM-D changes. Amygdala subregion FC changes linked to 5-HT1A/2A receptors. Impact: Correlations between FC changes of the amygdala subregions and the serotoninergic system activity after BLT may underline the antidepressant mechanisms of BLT. Combining baseline static and dynamic FC of the amygdala may assess the effectiveness of BLT in treating StD.