The mechanisms of early learning have been difficult to study becuase of the limited behavioral repertoire of infants and the lack of suitable rewards. An emerging understanding of the development of ingestive behavior in rat pups now provides a motivational system in which to examine appetitive learning in infants. Aspects of appetitive learning will be investigated in four groups of experiments: (1) Two similar forms of early learning, conditioned orientation and response conditioning, will be compared to define their similarities and differences. Both forms of conditioning occur when maternally and nutritionally deprived infants are rewarded with small oral infusions of milk. These infusions produce a marked behavioral activation or excitement at the time they occur, and this activation may reflect the actions of underlying neural reward mechanisms. (2) Experiments are proposed to evaluate the importance of activation to learning, and to determine what critical sensory and nutritive events during deprivation are responsible for it. (3) To assess whether similar factors have longer-term effects on behavioral development, pups will be studied during and after periods of artificial rearing, a procedure which allows close control and manipulation of pups' rearing experience. Findings from this study, regarding how sensory and nutritive events influence activity patterns and later reactivity, could have implications for intervention and diagnosis in infant chronic-care nurseries. (4) These behavioral analyses provide a basis for investigation of the neural mechanisms in early learning. Deoxyglucose autoradiography will be used to examine changes in patterns of neural activity in pups that are being trained or rewarded, and in pups responding to stimuli to which they have previously been conditioned. Each of these four proposed investigations is based on a conceptualization of learning as part of a broader system of infant adaptive behavior, and each is designed to take advantage of unique opportunities existing during development to dissect behavioral processes and to relate them to neural mechanisms.
