Z01 HD 001123-13 LCE and Z01 HD 001124-13 LCE are companion projects that together investigate auditory communication in primates. The overall goal of these studies is to provide a comprehensive understanding of primate auditory communication in terms of development, neural mechanisms, endocrine factors, and social context. Two non-human primates, the squirrel monkey and common marmoset, are the main subjects of study, with additional data collected from other species where appropriate. Prior work in this project has shown that production of sounds that are the functional and acoustic equivalents of cry sounds in human infants are mediated by limbic cortex located along the anterior midline of the frontal lobe of the cerebral cortex, and that single neural elements in the auditory cortex (superior temporal gyrus) are particularly responsive to subtle differences in the acoustic structure of species-specific vocalizations, suggesting an important role in mediating individual differences (vocal signatures). Studies of endocrine mechanisms in marmosets have shown that endogenous prolactin levels correlate with carrying time in infant retrieval tests, and that reducing prolactin by administering bromocryptine (a dopamine agonist) disrupts infant retrieval. Using a method for collecting urine samples noninvasively from social groups of squirrel monkeys has shown that prolactin is elevated when infants are present in this species, as well. The impact of actively playing juveniles on adult stress levels has been tested in squirrel monkey groups, with elevated cortisol (a measure of stress) associated with the presence of playing juveniles. New findings are (a) immunocytochemical processing for expression of Fos (the protein product of the c-fos gene) in brain sections from infant marmosets following a period of robust vocalizing revealed label in the hypothalamus and periaqueductal gray of the midbrain, but no label in the anterior cingulate gyrus (which has been implicated in production of adult vocalizations in squirrel monkeys); (b) collaborative studies involving human parents and their infants showed that parents can select their own infant's cry from an audio library including the cries of unfamiliar infants with high reliability. The neural substrates underlying recognition of infant cries will be the focus of future studies in human and nonhuman primate parents.