The relationship between heart rate variability, auditory evoked heart rate responses, and performance on recognition memory tests in low birth weight and normal birth weight infant macaques (Macaca nemestrina)

Abstract

This study describes heart rate variability (HRV) in the first two months of life and explores the relationships between HRV, auditory evoked heart rate responses and performance on tests of visual recognition memory (VRM). A sample of 9 low birth weight (LBW) and 15 normal birth weight (NBW) infant monkeys was studied.Measures of HRV including heart period, standard deviation, and RMSSD were obtained from five minutes of heart period data collected during sleep at six estimated postconceptional days of age: 175, 180, 190, 200, 210, and 230. Spectral analysis HRV measures were also computed. Heart rate responses to a series of auditory stimuli were tested at age 200. Performance on visual recognition memory problems was assessed at: 180, 190, 200, and 210 days of age.The NBW group had a developmental pattern for heart period and HRV which started out higher at the early ages of 175 and 180, dropped to a low level at age 190 and began to rise again at 200 days of postconceptional age. The LBW group had a similar pattern which was not statistically significant. Values for LBW and NBW groups did not differ significantly. HRV measures were not stable for individuals across time for either group of infants.LBW infants had a more marked biphasic HR response to the auditory stimuli and habituated more slowly. Infants with higher HRV during sleep had a greater response to the auditory evoked heart rate testing. No relationship was found between measures of HRV and performance on VRM.The failure to find differences in HRV measures between groups or to find individual differences which were stable across time mitigates against concluding that HRV is indicative of inherent autonomically based self-regulatory abilities or predictive of future cognitive outcomes. A macaque model for studying HRV was supported.