Estimating the stability of heartbeat counting in middle childhood: a twin study

There is growing interest in interoception, the perception of the body’s internal state, and its relevance for health and higher-order cognition across development. To date, most evidence linking interoception to health and cognition has used the heartbeat counting task. However, the stability of the measure across time, particularly during childhood, and the etiological factors that underlie individual differences in stability remain largely unexamined. Using data from the ECHO twin sample (N=204 twin pairs), we estimated the magnitude of genetic and environmental influences on the stability of heartbeat counting across a two-year period (8-10 years), the longest time-frame examined. We found a relatively modest correlation between heartbeat counting accuracy across time (r=.35), with accuracy on the heartbeat counting task improving with age. In our longitudinal twin analysis, we found that the heritability of heartbeat counting dropped between Time 1 and Time 2 from 30% to 6%. No new genetic influences were observed at Time 2, suggesting that genetic influences across this age-range are entirely stable. In contrast, shared environmental influences increased from 6% to 22%, with most of the influence at Time 2 due to new environmental factors. Of note, nonshared environmental factors accounted for the greatest proportion of variance at both time points, 64% and 73% respectively, and were the main contributors to temporal stability in heartbeat counting accuracy. Future research should seek to identify these non-shared environmental factors and elucidate whether this relatively modest stability reflects variability of interoception across development or unreliability of the heartbeat counting task.