experienced by a pregnant female can alter the structure of her
offspring’s brain, particularly regions vital for emotional
development, scientists have discovered.
in rodents at least, the effects differ in male and female
offspring. That might help explain the different
susceptibilities of men and women to emotional and psychiatric
disorders, says Katharina Braun, from the University of
Magdeburg, in Germany. Braun presented the work at the
Federation of European Neuroscience Societies' annual meeting in
Vienna, Austria, on Tuesday.
colleagues at the University of Jerusalem in Israel studied the
effects of stress on pregnant rats. If they become stressed in
the last trimester of pregnancy, their offspring developed fewer
nerve connections in two brain regions that control emotions –
the cingulate cortex and orbitofrontal cortex.
the nerve cells in several other regions show different
branching patterns to normal, with different effects on males
and females. In the hippocampus, an important region that
controls memory and emotion, males show an increase in branching
while females show a decrease. In the prefrontal cortex, the
males develop shorter nerve branches, while the females do not.
Braun has not
yet tested the behavioural effects of these changes on adult
rats, but the results could reveal a possible mechanism for the
development of emotional disorders seen in humans.
Boys are more
likely to develop attention deficit hyperactivity disorder
(ADHD) than girls – a disorder that seems to be related to the
brain's prefrontal attention systems, while women are more
likely to develop depression, which is known to be related to
shrinkage in the hippocampus.
experiences, especially emotional experiences, shape brain
circuits for later life,” says Braun. The susceptibility to
stress continues after birth, with different types of stress and
trauma leading to different brain effects, she adds.
daily painful stimuli given to young rodent pups, or separation
from their mother, each led to changes in the prefrontal cortex.
But while separation led to more nerve connections, painful
stimuli led to fewer.
experiments on brush tail rats – which are unusual in that the
father helps care for the offspring – showed that removal of the
father early in the pups’ life also leads to fewer neuron
connections in the brain's emotion centres.
The pups grow
up underactive and do not respond to the voices of their
mothers. Animals that were emotionally deprived seem to develop
emotional and social deficits.
compared the results to the sad experiences of Romanian orphans.
“Like the animal brain, the human brain needs to learn the
grammar of emotions,” she says. “Children after they are adopted
catch up nicely on cognitive level, but the emotional side looks
like it has been somehow frozen.” (See
Orphaned boys and girls react
differently to care .)
“We are now
collaborating with psychiatrists, asking questions such as 'Can
these effects be reversed?',” says Braun. Knowing when the adult
brain loses the flexibility of the young brain will be
important, she says.
Some evidence for hope came from
work by Igor Branchi, at the University of Rome in Italy. He
reported that when rodents were allowed extra social stimulation
– the mouse equivalent of kindergarten – a lot of early
emotional deficits could be improved.
2:02 12 July 2006
NewScientist.com news service
Helen Philips, Vienna