Nesting, nursing and grooming: these are some of the most crucial steps in the process of raising young. They are steps taken throughout the animal kingdom, with equivalents found in most nurturing species, including humans.
Scientists, for ages, have hypothesized and measured the changes in infant brains following weaning. But in a historical first, a group of researchers watched the changes occur in real time.
Researchers at NYU Langone Medical Center found that a mother's nurturing behavior shapes the neural activity quite early in her offspring. The presence of the mother can control the neuronal signaling that occurs in the baby's brain.
The researchers found that the signaling patterns seen between the first 12 and 20 days of a rat pup's life are quite similar to those patterns seen in a meditating, sleeping or highly focused human brain. During these early stages in infant brains, permanent communication pathways form between neurons, and nerve axons (projections of neurons) become covered in a fatty layer called myelin to speed up signaling. These processes are crucial to proper development of the infant brain.
"Our research shows how in mammals the mother's sensory stimulation helps sculpt and mold the infant's growing brain...and offers overall greater insight into what constitutes good mothering," says Regina Sullivan, a professor at NYU School of Medicine, in a press release.
The research gives a close glimpse into some of the ways variations in mothering cause variations in behavior among animals, including people, with "similar backgrounds, or uniform, tightly knit cultures," says Sullivan.
The study involved six rat mothers and their litters. One pup from each litter had a wireless transmitter implanted right under the skin, beside the brain, to pick up recordings of electrical patterns.
When the mothers left the litters, the pups displayed a jump in cortical brain electrical activity from 50 to 100 percent. Wave patterns became irregular and inconsistent. However, the researchers explained that this erratic pattern is important for healthy development of the brain and the signaling between different regions.
While nursed by their mothers, the pups' brain activities slowed and became more consistent. Bursts of electric activity, twice or five times the previous bursts, occurred during nursing. As the pups grew and became more independent, the researchers saw that these brain surges declined. On the outside, they saw the pups leave the nest more often in search of their own food.
They also found that much of the effects of nurturing are controlled by a neurotransmitter called norepinephrine. When this neurotransmitter was blocked, the effects of nursing and weaning were reduced significantly.
The team hopes to create tools and therapies for people whose brains may have been impaired or underdeveloped in infancy. The rat model studies help to understand exactly what happens during nurturing that is so essential to infant brain development.
"There are so many factors that go into rearing children," says Emma Sarro, lead investigator of the study, which was published in Current Biology. "Our findings will help scientists and clinicians better understand the whole-brain implications of quality interactions and bonding."