When the inner clock fades: Interoceptive decline and consolidation of phase resetting in cortical rhythms by cardiac events underlie healthy lifespan aging.

The integration of internal bodily signals with ongoing neural activity is fundamental to adaptive brain function and the maintenance of homeostasis. Among these signals, cardiac activity provides a continuous, quasi-periodic interoceptive input that interacts with intrinsic neural dynamics. Rather than functioning as a dedicated “internal clock” (), it is increasingly conceptualized as a temporally structured physiological rhythm that shapes cortical activity and contributes to perception, attention, and memory processes (, ) making it a tractable model for studying brain–body interactions. Aging is accompanied by widespread changes in cognition and brain function, including alterations in attention, emotion processing and subjective experience of time, together with large-scale changes in neural oscillatory activity and functional connectivity. Although these changes are well documented, the mechanisms underlying their emergence remain incompletely understood. Emerging evidence suggests that they may partly reflect alterations in the integration of internal bodily signals with ongoing neural activity (). For example, neural responses to individual heartbeats modulate conscious visual perception, demonstrating that cardiac signals can shape ongoing cortical activity and behavior (). Likewise, interoceptive awareness has been linked to the subjective experience of time, with individuals exhibiting greater sensitivity to bodily signals showing stronger alterations in perceived time passage (; ). Interestingly, subjective time perception itself changes across the lifespan, with many individuals reporting an apparent acceleration of time with advancing age (), a phenomenon also observed in neurodegenerative conditions such as Parkinson’s disease () and dementia (). Together, these findings raise an important question: how is the cortical representation of cardiac activity reorganized across the adult lifespan during the resting state, and what neural mechanisms underlie this reorganization? One promising avenue for investigating this interaction involves heartbeat-evoked responses (HERs), which reflects the brain’s response to afferent cardiac signals (; ; ; ; ). Cardiac signals reach the insula, Anterior cingulate cortex (ACC), Orbitofrontal cortex (OFC), and related regions via vagal and spinal pathways (). HERs have been implicated in a wide range of cognitive and affective processes, including arousal (), predictive coding (; ), interoceptive accuracy in emotional tasks (; ), heart disease (), somatosensory perception (), attention (), consciousness (), mental disorders (; ; ), time perception (), and, importantly, aging (). Importantly, HERs provide a neurophysiological index of interoceptive processing, rather than a direct measure of interoceptive accuracy or subjective awareness.