Luxotonic signals in human prefrontal cortex as a possible substrate for effects of light on mood and cognition

Animal studies revealed a mood-regulating neural pathway linking intrinsically photosensitive retinal ganglion cells (ipRGCs) and the prefrontal cortex (PFC), involved in the pathophysiology of mood disorders. As humans too have luminance-encoding ipRGCs, we asked whether a similar pathway exist in humans. Here, fMRI was used to identify PFC regions and other areas exhibiting luminance-dependent signals. We report 29 human brain regions where activation either monotonically decreased or increased with luminance. Luxotonic activity was identified across the cerebral cortex, in diverse subcortical structures, and in the cerebellum, regions that have functions related to visual image formation, motor control, cognition, emotion, and reward processing. Light suppressed PFC activation level, the activation monotonically decreasing with increasing luminance. The sustained time course of light-evoked PFC responses, and their susceptibility to prior light exposure, most closely resembled those of ipRGCs. These findings offer a functional link between light exposure and PFC-mediated cognitive and affective phenomena.