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July 19, 2000
Web posted at: 9:16 AM EDT (1316 GMT)

(AP) — Be grateful for the times Mom cooed over you and rocked you to sleep.
All of that fussing, it appears, may have made you smarter.

Experiments on rats by Canadian researchers suggest that mothers’ nurturing
stimulates neural connections in their babies’ brains and enhances learning. Those
offspring subsequently scored higher in intelligence and memory tests.

The researchers said the results, which appear in the August issue of Nature
Neuroscience, are broadly applicable to humans, too.

“It’s never nature vs. nurture. The influences are inseparable,” said Michael
Meaney, a neuroendocrinologist at McGill University who led the study. “Activity
of the genes is always influenced by the environment. And the most important
feature of the environment for an infant is mother.”

Other researchers described the findings as impressive.

“The stimulation provided by these mothers is certainly a large part of what
causes the brain to develop more extensively,” said neuroendocrinologist Bruce
McEwen of Rockefeller University in New York City.

However, some scientists cautioned against comparing rat and humans mothers
too closely, or attributing infants’ intelligence to relatively small differences in
parenting styles.

“I don’t want to put any more pressure on mothers,” said Rebecca Burwell, a
psychologist at Brown University. “The rat mothers showed differences in skills,
but they all were in the normal range. So it doesn’t really speak to parental abuse.
Some individuals may be very sensitive to subtle variations in parenting.”

In the experiment, the McGill team divided 32 female rats into two groups. One
group provided a high level of care to their offspring, including stroking,
grooming, licking and attentive nursing.

The other group included mothers that were more indifferent.

When the baby rats matured, they were tested in a swimming maze in which
they had to find a small platform submerged in a shallow tank. The rats were
tested 15 times over three days.

The rats scored about the same on the first day of testing. However, the
offspring of the attentive mothers scored higher on days two and three. The
smarter rats also scored high on other tests throughout their lives, he said.

The researchers then examined cells extracted from the hippocampus, a brain
region vital to memory and learning. In rats, cells in the hippocampus are
furiously connecting in the first days of life.

They found extra synapses, or connections between nerve cells, in samples from
the nurtured offspring. They also found more receptors for growth hormones
and the NMDA neurotransmitter that is crucial to learning.

The cells of the neglected offspring did not show similar enhancements.

“There is evidence for a direct relationship between maternal care and
hippocampal development, and spatial learning in adulthood,” Meaney said. “This
is experience-dependent development: Use it and it grows. Don’t, and it

In a second round of experiments, the researchers switched the offspring
between the good and neglectful mothers. Rats born to neglectful mothers but
raised by good mothers also scored well on the maze test and showed more
neural connections.

But rats born to attentive mothers but raised by indifferent mothers scored well,

Meaney said the findings suggest that proper nurturing can strongly influence
how the body carries out genetic instructions.

Social scientists said the experiments help to explain the biological underpinnings
of the mother-child relationship.

“Neglect is a form of abuse,” said Bruce Hershfield of the Child Welfare League
of America in Washington. “Young babies respond to the holding, the hugging,
the touching. Their brains grow, and it is important in the development of a
trusting relationships.”

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