Research

Regina M. Sullivan

Research Areas

Neonatal humans and rats.
Neurobiology of mammalian mother-infant attachment.
Ontogeny of memory.
Ontogeny and plasticity of olfactory and somatosensory systems

Our research explores the neural basis of attachment - how does an infant become attached to its caregiver? We research this question by using both infant rats and newborn human infants. Based on our basic research in rats, we suggest that the infant's brain is uniquely designed to ensure it quickly learns to like its mother regardless of whether the mother is treating it gently or harshly.

Basic research in rats:
We have developed a mammalian model of imprinting in which rat pups show unique learning during a neonatal sensitive period lasting until postnatal day (PN)10. This learning underlies attachment to the mother and is required for pup survival. Specifically, pups exhibit enhanced ability to acquire learned odor preferences and a decreased ability to acquire learned odor aversions. While heightened preference learning (attachment) is widely known to be a characteristic of infant learning, attenuated aversion learning is also quite common, and infant rats readily learn an odor preference from odor-shock conditioning. Similar preference/attachment learning is seen in infant chicks, puppies, and nonhuman primates, and clinical literature suggests this phenomenon is also expressed in abused human children. The young of these species are perfectly capable of feeling pain. As described below in rat pups, it is a specially designed brain that permits the learning of an attraction in painful situations. We hypothesized that this attachment system evolved across species to ensure altricial (dependent upon care at birth) animals easily form a repertoire of proximity-seeking behaviors to the caregiver, regardless of the quality of care-giving received.
Our research has identified a unique circuitry and functioning of the infant brain that underlies the unique learning abilities seen in attachment. Our work suggests 1) The locus coeruleus (LC) supports pups' heightened preference learning. While the LC is not necessary for adult learning, it is required for the neonate's sensitive period learning. 2) The lack of amygdala functioning underlies the attenuated ability to learn odor aversions. Specifically, the adult amygdala is used in both learned and natural fear (odor-shock conditioning is called fear conditioning). However, we have found that pups can only learn about fear when the amygdala functionally emerges, and this occurs as the sensitive period ends.

Clinically oriented human infant research:
The human infant must also learn about its caregiver. This learning begins during the first few hours of life and includes learning about the mother's odor. We have found that learned odors take on the characteristics of maternal odor. Specifically, similar to maternal odor, the newly learned odor appears to modulate behaviors used in interacting with the mother by causing the baby to turn to the source of the odor and begin mouthing, presumably in preparation for nursing.