Changes in Pregnancy May Boost Brain Power
Motherhood may make women smarter--perhaps permanently--as hormones released during pregnancy and nursing dramatically enrich parts of the brain involved in learning and memory, new animal studies suggest.
The findings, made public at a meeting of the Society for Neuroscience in Los Angeles, are among a series of emerging insights into how the subtle ebb and flow of sex hormones change the brain.
Indeed, so responsive is the female brain to changing hormone levels that aspects of neural cell structure appear to change during the course of a monthly cycle, new research indicates. Overall, researchers are discovering that, compared to the male brain, the female brain retains a remarkable capacity for change throughout a lifetime.
The enriching effects of child-bearing were discovered in an unusual series of experiments with laboratory animals by neuroscientists at the University of Richmond and Randolph Macon College in Virginia, who wanted to understand what effect the higher hormone levels of pregnancy had on brain structures involved in learning and memory.
Pictures of the brains reveal that special brain cell structures called dendrites--essential for communication between neurons--doubled in pregnant and nursing laboratory animals. At the same time, the number of the brain’s glial cells, which act as scaffolding and communication conduits, also doubled.
The mothering mice were bolder, more curious and energetic. They learned mazes more quickly, made fewer mistakes, and retained their new knowledge longer. And the effects appeared to be long-lasting, researchers found.
“We are seeing significant changes,” said Richmond neuro-psychologist Craig H. Kinsley, who conducted the study with Randolph Macon psychologist Kelly Lambert. “Pregnancy, a perfectly natural biological experience for the female, appears to mark the brain for a lifetime.
“In a way, the brain of a late-pregnant female resembles a toy factory at Christmastime, receiving orders and gearing up for the increased demands about to be placed on it,” Kinsley said. “It looks like this does something to make their learning much more efficient than females without that experience. It suggests there is a permanent change in that female’s behavior, reflective of some sort of permanent change in the brain.”
Findings at Odds With USC Research
The new findings are at odds with earlier clinical research at the University of Southern California that showed how pregnancy temporarily interferes with intellectual functions. Pregnant women performed poorly on a battery of cognitive tests designed to test memory, perceptual speed and learning ability. Other researchers discovered that women’s brains even shrink slightly during pregnancy, perhaps affecting concentration.
While no one is certain, some researchers attribute those feelings of fuzzy-mindedness among many expectant mothers to the emotional stresses of pregnancy, which provoke higher levels of a hormone called cortisol that interferes with memory.
The Richmond study, however, suggests that more fundamental changes in brain structure also may be at work, with the promise of a more lasting beneficial effect.
In recent decades, supplements of sex steroids have become powerful tools to control or alter human biology--from birth control pills and fertility drugs to muscle-building performance-enhancers and post-menopausal estrogen therapies. But only recently have scientists come to appreciate how these sex hormones continuously affect the brain.
Although researchers traditionally have focused on how sex hormones control reproduction, scientists have long been aware that these natural steroids--estrogen, progesterone and testosterone--set the basic gender mold of each brain.
Evidence of Changes in Nervous System
The newest pregnancy research adds to a small but growing body of evidence that demonstrates how reproductive experience can alter the nervous system.
Last year, for example, researchers at UC Berkeley reported on how sexual experience can change brain structure in male animals, by enlarging or shrinking nerve cells in the same manner as genetic changes.
In recent years, there has been a flood of evidence from imaging studies of the human brain that highlight how male and female thinking differ as a matter of brain function. Those differences in brain organization are controlled by powerful surges of hormones at crucial stages of prenatal development and then again during puberty.
But only now are scientists learning how these powerful steroids promote survival of brain cells, encourage new neural connections, guide the growth of many brain regions well into old age and prompt distinctively different cell structures in male and female brains.
“We are recognizing with some surprise the extent to which the brain responds to circulating levels of steroid hormones,” said Douglas Meinecke, chief of the developmental neuroscience program at the National Institute of Mental Health.
“These hormones--estrogen, testosterone and progesterone--have a profound effect on the brain,” Meinecke said. “And the brain is profoundly responsive to these hormones in many different places and times during development and throughout life.”
Demonstrating how fundamentally steroids influence the brain, researchers also reported at this week’s neuroscience conference that sex hormones:
* Influence which neurons survive in the male brain. Physiologist Margaret McCarthy at the University of Maryland Medical School also reported that testosterone and estrogen affect how the brain wires itself. In some parts of the brain, neural synapses differ dramatically in men and women. Glial cells also take different form in the male and female brains.
* Guide normal development of motor neurons and other areas of the nervous system. The hormones appear to promote the production and release of neural growth factors. Male hormones called androgens “are changing the nerve’s ability to gain protective support,” said researcher Nancy Forger, a psychologist at the University of Massachusetts at Amherst.
* Steer new brain cells into position during development. Stuart Tobet of the Shriver Center in Waltham, Mass., found that in the prenatal period, sex steroids and steroid receptors influence where different types of cells end up in the brain.
* Change the characteristics of brain cells in the hippocampus, which is involved in learning and memory. John Morrison, a neurobiology professor at Mt. Sinai Medical School in New York, found that the number of receptors on hippocampal cells fluctuates depending on estrogen levels.
“Hormones act throughout life on the brain but they don’t act the same throughout life,” McCarthy said. “They have very different effects at different times.”
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(BEGIN TEXT OF INFOBOX / INFOGRAPHIC)
Mothering the Brain
New laboratory studies suggest that hormones released during pregnancy and nursing may enrich parts of the brain responsible for learning and memory.
NEURON CELLS
Brain cell structures called dendrites, essential for communication between neurons, doubled in pregnant and nursing laboratory mice. Dendrites extend from the cell body of a neuron and receive messages from other neurons. Dendrites are covered with synapses, which serve as the contact points for communication between neurons.
Dendrites of mouse before pregnancy
Dendrites of pregnant mouse
Dendrites of nursing mouse
Dendrites
Nucleus
Neuron cell
****
GLIAL CELLS
The number of supporting brain cells, called glial cells, also doubled. Glial cells fill most of the space in the brain not occupied by neurons and blood vessels. They act as scaffolding and communication conduits, and play an important role in the growth of neurons.
Glial cells of mouse before pregnancy
Glial cells of pregnant mouse
Glial cells of nursing mouse
Glial cell
SOURCE: UNIVERSITY OF RICHMOND, RANDOLPH MACON COLLEGE, SOCIETY FOR NEUROSCIENCE
