Circadian rhythms in monkeys: Variability and behavioral correlations

Abstract

Heart rate (HR) and body temperature (BT) data were collected for a total of eighty 24-hour days from 5 infant pigtailed ( M. nemestrina) monkeys using totally implantable multichannel biotelemetry systems. Best fit (least squares) cosine functions were fit to each 24-hour block of HR and BT data providing estimates of circadian cosine level, amplitude and phase. Within animal correlations were computed among 6 cosine variables and these correlations were then pooled using Fisher's transformation. The relation between circadian variables and 26 daytime behavioral variables were also assessed. We found relatively large long term day to day changes in circadian HR and BT measures, especially HR level. BT level and HR level were correlated, and BT phase and HR phase covaried. Several measures of activity were found to have significant correlations with HR amplitude, while one measure of the nature of the mother-infant relationship was significantly correlated with HR level. It is hypothesized that variability in HR level may reflect long term alterations in autonomic nervous system balance.