Hub cells in the brain keep the body clock on time ^{CEFR B2}

Scientists at Washington University in St. Louis introduced a new computational tool called MITE (Mutual Information and Transfer Entropy), pronounced "mighty", to map directional communication between cells in the suprachiasmatic nucleus (SCN), the brain's central circadian pacemaker. The study, led by Professor Erik Herzog and KL Nikhil and published in the Proceedings of the National Academy of Sciences, combined weeks-long, cell-level recordings of gene expression with advanced information-theory analysis.

Using those recordings, the team reconstructed more than 25 million connections among over 8,000 cells across 17 mice, achieving over 95% accuracy. The maps reveal that, although the mouse SCN contains roughly 20,000 neurons, synchrony depends on a relatively small subset of highly connected hub cells. The researchers grouped cells into five functional types based on connection patterns.

• Highly connected hub cells, including a small subset of VIP-expressing neurons that broadcast synchrony signals.
• Bridge cells that relay signals from hubs to other network regions.
• Sink cells that receive converging signals and likely pass timing information to the rest of the body.

Computational tests showed that removing only the hub neurons caused synchrony across the network to collapse, which supports the idea that hub cells are critical to SCN timekeeping. The authors propose next steps to pinpoint how hubs exert influence and whether targeted interventions could tune SCN timing. This tool could aid efforts to realign the body clock and help shift workers, people affected by seasonal affective disorder, and others with circadian problems.