What turns a young female concerned mainly about herself into a good mother who will make sure her offspring survive in an otherwise hostile world? The bodily changes of childbearing are obvious, but as we are discovering, the changes in the brain are no less dramatic.
The maternal brain is a formidable object, a singular entity forged by hormones, neurochemicals, and exposure to the ravening demands and irresistible cuteness of offspring. During pregnancy, the female brain is effectively revving up for the difficult tasks that await. A mother-to-be may most notice her cravings for ice cream and pickles, but inside her head, a transformation is afoot in fundamental functions ranging from attention to memory. As an intriguing new paper demonstrates, even her sensitivity to others' emotions increases.
Before we describe the new paper, let us contemplate the maternal brain in all of its wet majesty. Among its remarkable changes are those that allow the mother to focus on her infant in the persistent attempt to puzzle out the child’s needs and wants. As any parent knows, the infant is inscrutable – indeed, the child remains so for much of the parent’s life – and intuition is the mother’s best friend. The parent tests hypotheses: Is the baby hungry? Tired? A sensitized brain facilitates these “experiments.” In humans, rodents and other animals, we find data showing that the mother’s interest in, and motivation toward young increases dramatically as pregnancy nears term, and still further immediately following birth.
Underlying such change is a manifest shift in neuronal size, activity and capacity. Neurons in the part of the brain that largely regulate maternal behavior, called the medial preoptic area (mPOA), grow impressively during late pregnancy, increasing the protein-synthesizing capabilities of the cell. Like a race-car burning rubber before the green light, these mPOA neurons are readying themselves to respond to offspring stimuli with appropriate and sensitized impulses.
Further, in another brain region, the hippocampus, neurons are undergoing changes of another sort, leading to increases in the concentration of tiny projections on the surface of dendrites, called dendritic spines. These dendritic spines provide more neuronal surface and are believed to regulate inter-neuronal commerce. That the spines are increasing in the hippocampus, which controls learning and memory, suggests a possible function: enhancing memory, particularly spatial memory, that may be required of the new mother.
Fittingly, many data from numerous labs show that females with offspring have an increased facility for remembering the location of food caches and rewards in a variety of spatial environments. These females -- particularly multiparous females, those with two or more pregnancies under their belts -- are especially good at these tasks. Now, think about why: a mother that must leave her nest to forage for food – or her home for work – exposes both herself and her young to risk of predators and may benefit from an enhancement to her foraging skills or to the economy of her behavior, in general. The cost:benefit ratio decreases if she can find food and get back as quickly as possible to her lonely and vulnerable offspring.
In their recent paper, Rebecca Pearson of the University of Bristol’s Academic Unit of Psychiatry and her co-authors add fuel to the race-car-burning-rubber theory. They find that not only are neurons ramping up their own activity levels, but that the hormones estrogen and progesterone are also intensifying emotive activity, helping mothers become more focused on their offspring and their offspring’s myriad cues.