Patterns (New York, N.Y.)Sep 16, 2026

Explainable machine learning shows uneven day-night switching between the brain's left and right internal clocks

Circadian Biology Weekly Brief ↗PubMed ↗DOI ↗

Updated Sep 17, 2026

Abstract

The suprachiasmatic nucleus (SCN) contains approximately 20,000 neurons organized into a bilaterally symmetric structure.

Distinct neural spatiotemporal states and subtypes were identified in SCN neurons.
Hemispheric asymmetry was observed, particularly during the subjective day.
Each hemisphere encoded a full yet unique representation of time features related to circadian rhythms.
Spectral features of calcium signals were found to be the primary elements distinguishing this asymmetry.
Hemispheric asymmetry of state switching may be a fundamental characteristic of the brain's circadian clock.

Simplified

The suprachiasmatic nucleus (SCN) is the master circadian clock in mammals, comprising ∼20,000 neurons organized into a bilaterally symmetric oval structure. System-level time computations in the SCN depend on coordinated spatiotemporal patterns of neuronal activity, yet most prevailing methods perform time-series analyses while disregarding neural spatiotemporal organization. Here, we developed an interpretable machine learning framework for the integrative analysis of large-scale spatiotemporal calcium signals from SCN neurons, with built-in validation and biological interpretability. Applying this framework, we identified distinct neural spatiotemporal states and subtypes whose spatial mapping across hemispheres revealed hemispheric asymmetry, particularly during the subjective day. Circadian timekeeping ability also displayed side specificity, with each hemisphere encoding a full yet unique time feature representation. Attribution analysis further indicated spectral features of calcium signals as the primary discriminative elements underlying this asymmetry. Overall, we demonstrate that hemispheric asymmetry of state switching is a fundamental property of the brain's circadian clock.

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Explainable machine learning shows uneven day-night switching between the brain's left and right internal clocks

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