Parenting and plasticity

Abstract

As any new parent knows, having a baby provides opportunities for enrichment, learning and stress - experiences known to change the adult brain. Yet surprisingly little is known about the effects of maternal experience, and even less about the effects of paternal experience, on neural circuitry not directly involved in parenting. Here we discuss how caregiving and the accompanying experiential and hormonal changes influence the hippocampus and prefrontal cortex, brain regions involved in cognition and mood regulation. A better understanding of how parenting impacts the brain is likely to help in devising strategies for treating parental depression, a condition that can have serious cognitive and mental health consequences for children.

Figure 1

Parental experience produces changes in structural plasticity in the hippocampus and PFC. Top: Schematic diagram of the hippocampus showing the dentate gyrus, the location of adult neurogenesis (boxed area indicates region from which photomicrographs were obtained). Mother rats exhibit suppressed adult neurogenesis in the dentate gyrus prior to weaning of their offspring. (a) Virgin female rats have more proliferating cells, labeled here with the thymidine analog bromodeoxyuridine (BrdU) (arrows), compared with postpartum rats (b). BrdU-labeled cells are stained brown and cells labeled for Nissl are stained purple. Scale bar, 20 μm. Bottom: Schematic diagram of cortical layers (I–VI) in the PFC showing the neuron type affected by parenting (boxed area indicates layers II/III, where changes were detected in pyramidal neurons). Father marmosets exhibit enhanced dendritic spine density on pyramidal neurons of layer II/III PFC compared to non-fathers. (c) Layer II/III PFC pyramidal cell of a marmoset father labeled with the lipophilic tracer DiI (fluorescent green). Magnified views of DiI labeled dendritic segments showing dendritic spines (arrows) in a control (right upper) and a father (right lower). Scale bar, 30 μm for cell, 5 μm for dendritic segments. Adapted, with permission, from Ref. [25,73].

Figure 2

Parenting can alter anxiety and cognition by inducing structural changes through potentially different mechanisms. This model diagram illustrates some of the structural changes that occur with parenting, including suppressed neurogenesis in the dentate gyrus, reduced dendritic complexity in the CA3 pyramidal cell population of the hippocampus, and enhanced dendritic spine density in pyramidal cells of the CA1 hippocampal region and layer 2–3 of the PFC. Parenting-induced elevated glucocorticoid levels might underlie changes in the dentate gyrus and CA3 regions of the hippocampus, whereas the enriching aspects of infant contact might produce changes in the CA1 region and PFC. Changes in the structure of the hippocampus and PFC might be responsible for parenting-induced alterations in behaviors associated with these brain regions, including reduced anxiety-like behavior and enhanced cognition. Photo credit: J. Alberts (University of Indiana).