Uncovering the Brain's Role in Circadian Regulation and Jet Lag Adaptation

Recent advancements in deep brain imaging have shed light on the intricate mechanisms governing our internal biological clock, especially in how it adapts to changes such as crossing time zones. The circadian clock, an internal system that influences sleep, metabolism, immune response, and alertness, is primarily regulated by the suprachiasmatic nucleus (SCN) located deep within the hypothalamus. This tiny yet vital brain region coordinates our 24-hour rhythms, aligning them with daylight cycles.

When we travel across multiple time zones, our internal clock struggles to synchronize with the external environment, leading to jet lag. Although it is known that specialized cells in the eye called intrinsically photosensitive retinal ganglion cells detect blue light and send signals to reset the SCN, the specific neuronal responses within this nucleus have remained obscure.

A groundbreaking study published in Nature Communications, led by researchers from National Taiwan University and National Tsing Hua University, utilized the most detailed two-photon calcium imaging in awake mice to observe how individual neurons in the SCN respond to light stimuli. Challenging existing assumptions, the findings revealed that the process of light-induced clock resetting is far more complex than the previously believed simple relay of signals.

The researchers found that certain neurons are activated by light, while others are inhibited. Remarkably, despite the variability in which neurons respond in each trial, the overall balance between activation and inhibition remains consistent. This suggests that the SCN functions more like a dynamic network capable of complex computations, akin to decision-making regions in higher brain areas.

Further investigations identified a specific subset of neurons that are activated by light during the early night and play a crucial role in delaying the internal clock. By artificially stimulating these neurons, scientists could shift the mice’s circadian rhythm later, even during times when the system normally ignores light signals. This discovery opens up potential avenues for developing interventions to speed up jet lag recovery or assist late sleepers in adjusting more easily.

Professor Shih-Kuo Chen highlighted the broader implications, noting that understanding these neuronal circuits could lead to innovative treatments for circadian-related disorders such as insomnia and jet lag. Instead of viewing circadian adjustment as straightforward, these findings underscore the brain’s intricate network and its capacity for adaptable regulation of our biological timekeeping.

Overall, this research revolutionizes our understanding of how the central clock in the brain integrates external light cues and provides a promising foundation for future therapies aligned with the body’s natural rhythms.

source: https://medicalxpress.com/news/2025-06-rewiring-body-clock-deep-brain.html