Light Impact on Thalamo-Cortical Connectivity During a Cognitive Task Depends on Time of Day and is Different in Teenagers

BackgroundLight 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. MethodsUsing 7-Tesla fMRI, this study examined how light illuminance modulates canonical left-lateralized verbal thalamo-prefrontal-parietal network connectivity during an auditory executive task. Fifty-five participants, including young adults (19-30 y, 23 Females: scanned in the morning or evening) and adolescents (15-18 y, 6 Females: scanned only in the evening), were studied. ResultsWe first found that across all the groups, moderate blue-enriched light strengthened parietal-to-frontal connectivity, while low-illuminance orange light enhanced thalamus-to-parietal connectivity. When focusing on time-of-day differences in young adults, we found that higher-illuminance blue-enriched light strengthened thalamus-to-prefrontal connectivity in the morning compared to the evening. When focusing on developmental stages differences, during the evening session only, we observe that moderate blue-enriched light enhanced thalamus-to-parietal connectivity in adolescents compared to young adults. ConclusionThese findings reinforce the view that the thalamus plays a key role in mediating the impact of light on cognition and the impact of light depends on the context of light administration, i.e. with timing and age.