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

Studies with experimental animals have 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. Since humans also have light-intensity-encoding ipRGCs, we asked whether a similar pathway exists in humans. Here, functional MRI was used to identify PFC regions and other areas exhibiting light-intensity-dependent signals. We report 26 human brain regions having activation that either monotonically decreases or monotonically increases with light intensity. Luxotonic-related activation occurred across the cerebral cortex, in diverse subcortical structures, and in the cerebellum, encompassing regions with functions related to visual image formation, motor control, cognition, and emotion. Light suppressed PFC activation, which monotonically decreased with increasing light intensity. The sustained time course of light-evoked PFC responses and their susceptibility to prior light exposure resembled those of ipRGCs. These findings offer a functional link between light exposure and PFC-mediated cognitive and affective phenomena.

Automated summary

Studies with experimental animals have found a neural pathway connecting intrinsically photosensitive retinal ganglion cells (ipRGCs) and the prefrontal cortex (PFC) that is involved in mood disorders. This study aimed to investigate whether a similar pathway exists in humans. Functional MRI analysis revealed activation in 26 human brain regions that either decreased or increased monotonically with light intensity, including regions related to visual image formation, motor control, cognition, and emotion. PFC activation was suppressed by light, decreasing monotonically with increasing light intensity. The sustained time course and susceptibility to prior light exposure of light-evoked PFC responses resembled those of ipRGCs. These findings provide a functional link between light exposure and PFC-mediated cognitive and affective phenomena.