Light Impact on Thalamo-Cortical Connectivity During an Executive Cognitive Task: Effects of Time of Day and Specificities of Teenagers

Light affects not only vision but also attention, alertness, and cognition, primarily through intrinsically photosensitive retinal ganglion cells sensitive to blue-wavelength light. While previous research has shown that light influences brain regional activity, its impact on brain connectivity remains unclear. Using 7-Tesla fMRI, this study examined how light modulates thalamo-cortical connectivity during an auditory executive task involving the thalamus, the prefrontal cortex (in supramarginal gyrus : SMG), and parietal cortex (in the inferior frontal junction : IFJ). Fifty-five participants, including young adults (19-30y: scanned in the morning or evening) and adolescents (15-16y: scanned in the evening), were studied. Across all groups, moderate blue-enriched light strengthened SMG-to-IFJ connectivity, while low-illuminance orange light enhanced thalamus-to-SMG connectivity. High-illuminance blue-enriched light strengthened thalamus-to-IFJ connectivity only in the morning for young adults, while moderate blue-enriched light enhanced thalamus-to-SMG connectivity in adolescents in the evening. These findings suggest that the thalamus plays a key role in mediating cognitive effects of light and timing and age influence non-image-forming responses.