Study in Tree Shrews Uncovers Brain Circuit Connecting Nighttime Light Exposure and Depression

A recent groundbreaking study published in the Proceedings of the National Academy of Sciences has shed light on how artificial light exposure at night (LAN) may influence mood and mental health. Conducted on tree shrews—small diurnal mammals genetically close to primates—the research explored how prolonged exposure to blue light during nighttime hours can induce depression-like behaviors. The scientists found that exposing these animals to blue light for two hours nightly over three weeks led to notable symptoms such as reduced interest in pleasurable activities (measured by decreased sucrose preference), decreased exploratory behavior, and impaired long-term memory.

Using sophisticated neural tracing methods, the researchers identified a specific visual pathway that mediates these effects. They discovered that retinal ganglion cells send direct signals to the perihabenular nucleus (pHb), which then projects to the nucleus accumbens—a vital brain region involved in mood regulation. Notably, silencing the pHb neurons prevented the mice from exhibiting depression-like symptoms despite ongoing light exposure, suggesting that this pathway plays a crucial role in mediating LAN-induced mood changes. Further genetic analysis showed alterations in depression-related gene activity, indicating potential long-lasting effects of such light exposure.

Given the rising prevalence of light pollution and increased screen time in modern society, these findings raise important concerns about the psychological impacts of artificial lighting. The study emphasizes that while artificial light supports our productivity and convenience, it may also be subtly reshaping brain circuits linked to mood disorders. Experts like Prof. Yao Yonggang highlight the importance of understanding these neural pathways to develop targeted interventions that could mitigate adverse mental health effects while maintaining the benefits of nighttime lighting.

This research offers valuable insights into the biological mechanisms underlying the relationship between artificial light and depression, paving the way for future therapies aimed at protecting mental health in our illuminated world.