The European journal of neuroscienceDec 15, 2010

Daily and seasonal adjustment of the body’s internal clock needs flexibility in the brain’s timekeeping neurons

Circadian Biology Weekly Brief ↗PubMed ↗DOI ↗

Updated Mar 21, 2026

Abstract

Circadian rhythms, governed by an internal clock in the suprachiasmatic nucleus (SCN), are essential for many living organisms.

Basic adaptive functions of the circadian system may depend on changes in the organization of neuronal networks.
Photic entrainment adjusts the circadian clock to align with the light-dark cycle.
Seasonal adaptation of the clock is influenced by changes in day length.
Plasticity in the phase relationship between different regions of the SCN is observed during environmental cycle adjustments.
Both photic entrainment and seasonal adaptation involve a redistribution of oscillatory activity patterns within the SCN, but utilize different neuronal coupling mechanisms.

Simplified

Circadian rhythms are an essential property of many living organisms, and arise from an internal pacemaker, or clock. In mammals, this clock resides in the suprachiasmatic nucleus (SCN) of the hypothalamus, and generates an intrinsic circadian rhythm that is transmitted to other parts of the CNS. We will review the evidence that basic adaptive functions of the circadian system rely on functional plasticity in the neuronal network organization, and involve a change in phase relation among oscillatory neurons. We will illustrate this for: (i) photic entrainment of the circadian clock to the light-dark cycle; and (ii) seasonal adaptation of the clock to changes in day length. Molecular studies have shown plasticity in the phase relation between the ventral and dorsal SCN during adjustment to a shifted environmental cycle. Seasonal adaptation relies predominantly on plasticity in the phase relation between the rostral and caudal SCN. Electrical activity is integrated in the SCN, and appears to reflect the sum of the differently phased molecular expression patterns. While both photic entrainment and seasonal adaptation arise from a redistribution of SCN oscillatory activity patterns, different neuronal coupling mechanisms are employed, which are reviewed in the present paper.

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Daily and seasonal adjustment of the body’s internal clock needs flexibility in the brain’s timekeeping neurons

Abstract

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