When Light Influences Mood: The Amygdala at the Heart of Seasonality
Light is far more than a simple vehicle for vision. For decades, researchers have known that it exerts “non-visual effects” on our bodies: synchronizing the biological clock, regulating melatonin, modulating mood, and boosting attention. These effects rely on specific retinal photoreceptors sensitive to blue light thanks to a pigment called melanopsin.
Yet, the brain mechanisms that translate these light signals into emotional responses remain largely unknown. That’s precisely what Gilles Vandewalle’s team at the Sleep and Health Laboratory (GIGA Neuroscience) set out to explore: “We wanted to understand whether light’s impact on mood could be explained by the activity of certain parts of the amygdala, a central structure in emotion processing,” he explains.
Using 7-Tesla magnetic resonance imaging, the researchers analyzed the amygdala’s nuclei. Twenty-nine volunteers (men and women) were exposed to lights of varying intensities while listening to emotional or neutral sounds. The results show that the activity of certain medial and superior amygdala nuclei varies with the seasons and photoperiod. “We observed the strongest impact of light at the beginning of summer, around the solstice,” notes Gilles Vandewalle.
These findings confirm that humans exhibit seasonality and that light plays a decisive role in this phenomenon. This seasonality could influence mood by involving specific parts of the amygdala.
The research opens therapeutic perspectives: “Understanding these mechanisms helps us explain why light therapy is effective against certain mood disorders, such as seasonal depression and other types of depression,” the researcher emphasizes.
In other words, light doesn’t just set the rhythm of our days, it communicates with our brain, subtly shaping our emotions. An interaction that could illuminate new paths for mental health.
Reference
Regional activity within the human amygdala varies with season, mood and illuminance
Islay Campbell*, Jose Fermin Balda Aizpurua*, Roya Sharifpour, Ilenia Paparella, Elise Beckers, Nasrin Mortazavi, John Read, Christophe Phillips, Fabienne Collette, Puneet Talwar, Laurent Lamalle, Mikhail Zubkov, Gilles Vandewalle
GIGA-CRC-Human Imaging, University of Liège, Liège, 4000 Belgium
