Studied the autonomic regulation of 37 infants with a typical cry threshold and 17 infants with a high cry threshold (typical of problems in nervous system function). Infants with a high cry threshold had a longer latency to cry, a shorter first cry sound, and a shorter overall bout of crying. Spectrum analysis of 2 hours of heart rate variability showed that a high cry threshold was predictive of fewer reliable rhythms and a lower power of the basic 40-min rhythm in heart rate. High cry threshold infants also showed fewer startles and changes in behavioral state. Results suggest a high cry threshold predicts disrupted autonomic regulation and poor coordination among rhythmic systems affecting cardiac activity.

The rhythmic organization underlying long-term heart rate variability was examined in 36 newborn infants. Heart rate was registered every 30 s for 2 continuous hr while infants rested in a temperature-controlled isolette. Spectrum analysis of the time-series of the 240 observations detected rhythmically organized changes in the heart rates of 33 of the 36 infants. Thirty of the 33 infants showed a basic rhythm at 1.5 +/- .5 cycles per hr (one cycle every 30 to 60 min). While 9 infants showed this single cycle in behavioral activity, 24 infants showed additional cycles at a wide range of faster frequencies. Infants with signs of atypical fetal growth less often showed evidence of these multiple cycles, had reliably fewer cycles in heart rate, and had a marginally lower power in their basic cycle than infants with typical patterns of fetal growth. Infants with multiple cycles in the power spectra, independent of fetal growth group, were more often observed in Alert and Active Alert behavioral states and less often in Active Sleep than comparison infants. Results indicate that 1) heart rates of newborn infants show evidence of the 30- to 60-min cycle characteristic of the Basic Rest-Activity Cycle found in other behaviors, and 2) the complexity of behavioral rhythms may be affected by prenatal malnutrition. Viewed within a dynamical systems approach to development, results suggest that the complexity of rhythms in behavior may reflect the complexity of behavioral organization.

A large sample of pigeons (n = 458) was trained in a classical conditioning paradigm where whole-field retinal illumination and foots hock were paired to produce conditioned heart-rate change. Analysis of the acquisition data indicated two distinct learning patterns (denoted C and C), and any given group of animals can be ~haracterized by describing the proportion of animals showing each acquisition pattern (the C:C ratio). It is shown that mean learning curve variability among groups is largely a function of group differences in this ratio, such that accurate prediction of mean learning curves is possible knowing only this parameter. Furthermore, this ratio is itself predictable only from responses to an initial visual stimulus presentation. Consequently, from reactivity (orienting response) to a single presentation of the to-be-conditioned stimulus, it is possible to predict accurately the mean learning curve of any given group.

Heart rates and behavioural states of 14 breast-fed and 14 bottlefed newborn infants were assessed every 30 seconds for 2 continuous hours. The 240 observations of heart rate were treated as time-series data and spectrum-analysed for behavioural rhythmicities. Of the 28 infants, 25 showed reliable cycles in heart rate; 22 of the 25 infants showed a dominant frequency with a 30-60 min periodicity, one that approximates the basic-rest activity cycle (BRAC). In addition to this basic cycle, additional higher frequency cycles in long-term heart rate variability were evident in the spectra of many infants. Breast-fed newborns had greater numbers of reliable cycles in heart rate than bottle-fed newborns. Further, breast-fed newborns had lower overall mean heart rates and lower mean heart rates in Quiet and Active Sleep states than bottle-fed newborns. Bottle-fed newborns were observed more often in Quiet Sleep than breast-fed newborns. Without knowledge of the specific mechanisms causing these behavioural differences, the results of this study suggest that the context in which breast-feeding occurs results in a more complex and energy-efficient pattern of behavioural organization than the context of bottle-feeding.

No abstract