Offspring-induced nurturance: animal-human parallels.

Offspring provide mothers with stimuli that impel their own nurturance. In rats, distal sensory stimuli from pups--sight, sound, odor--contribute to contact-seeking, whereas tactile stimuli from pups to dam's snout and ventrum elicit essential maternal behavioral reflexes involved in retrieval, licking, and the quiescent, upright nursing posture (kyphosis). Brain sites involved with maternal behavior--assessed by lesions, immunocytochemical visualization of gene activity, and neurophysiological mapping--include the midbrain central gray, medial preoptic nucleus, limbic system, and somatosensory cortex; these may change with experience. Human mothers inadvertently learn to identify their own baby rapidly after birth and can do so via a single sensory modality. Subsequently maternal responsiveness and gratification are impaired by inappropriate, insufficient, or nonreciprocal interactions such as occurs when the baby cries excessively, is blind, deaf, or autistic. Thus, maternal behavior characterized by elicited responses and emotional reactions to stimuli from offspring may be evolutionarily conserved.