Age associated alterations in the cortical representation of cardiac signals: A heartfelt tale

Neural representation of cardiac rhythms, known as heartbeat evoked responses (HERs), provide a avenue for investigating the interaction between the brain and the heart, pivotal for various physiological and cognitive functions. Concomitantly, age is recognized as a significant factor influencing this interaction, given its impact on both the structural and functional aspects of the brain and the cardiovascular system. Nonetheless, the precise nature of this interaction during the healthy ageing process remains elusive. This study aims to investigate how the influence of cardiac rhythms on spontaneous brain activity varies with age, using HERs as a measure. Subsequently, it aims to explore the mechanism underlying HERs generation and characterize the brain networks that prominently represent HERs from a large (N = 620) human healthy ageing dataset (18-88 years). The results show that HERs exhibit time-locked activity around 180-320 ms post R-peak of the electrocardiogram (ECG) waveform, with significant decrease in HER amplitude across age for both the genders. Furthermore, inter-trial phase coherence (ITPC) analysis indicates that cardiac signals modulate the phases of the ongoing neural oscillations rather than altering the spectral power. Causal functional maps among brain areas computed using Granger causality (GC) reveals consistent connectivity in the fronto-temporal network, though with varying strength across age groups revealing a compensatory mechanism in play to maintain homeostasis. Overall, these findings provide a comprehensive understanding of the interaction between heart and brain in healthy ageing and present opportunities to identify non-invasive markers for characterizing pathological development in neurological and cardiovascular functions.