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cortex loses neurons during adolescence, researchers find
Life Sciences Editor
photo to enlarge
by L. Brian Stauffer
professor Janice Juraska, right, and graduate student
Julie Markham have found that adolescents begin to
lose neurons in the prefrontal cortex.
CHAMPAIGN, Ill. —
Researchers at the University of Illinois have found that adolescence
is a time of remodeling in the prefrontal cortex, a brain structure
dedicated to higher functions such as planning and social behaviors.
The study of rats found that both males and females lose neurons in
the ventral prefrontal cortex between adolescence and adulthood, with
females losing about 13 percent more neurons in this brain region than
This is the first study to demonstrate that the number of neurons in
the prefrontal cortex decreases during adolescence. It is also the first
to document sex differences in the number of neurons in the PFC. The
study appears in the Feb. 9 issue of the journal Neuroscience.
Earlier studies in humans have found gradual reductions in the volume
of the prefrontal cortex from adolescence to adulthood, said psychology professor and principal investigator Janice M. Juraska. “But the
finding that neurons are actually dying is completely new. This indicates
that the brain reorganizes in a very fundamental way in adolescence.”
Juraska, graduate student Julie Markham and undergraduate student John
Morris found that the number of neurons decreased in the ventral, but
not dorsal, prefrontal cortex during adolescence. The number of glial
cells, which surround and support the neurons, remained stable in the
ventral PFC and increased in the dorsal PFC.
These findings challenge current models of brain development by showing
that some parts of the brain are still being organized well after puberty.
This could have implications for understanding human psychopathologies,
such as schizophrenia, which often arise in late adolescence, Juraska
Other psychological conditions, such as depression, often first occur
in adolescence. And alcohol and nicotine addictions that start in adolescence
are harder to overcome than those that begin in adulthood, Juraska said.
“We know that experiences are very potent in younger children
because their brains are developing,” Juraska said. “So
if there is another time that the brain is changing, then everything
that happens can be written in and magnified more than during stable
The finding that females lose more neurons in the ventral PFC than males
during adolescence also is new. Juraska had found earlier that adult
female rats had fewer neurons than males in the visual cortex, a brain
region associated with perception. But no other studies have looked
for sex differences in the number of neurons in the prefrontal cortex.
It is unclear whether sex differences seen in the rat PFC also occur
in humans, Juraska said. One contributing factor may be that female
rats in the wild are almost always pregnant or nursing.
“The metabolic demands on female rats are so heavy that it might
be worthwhile to do away with some very costly cortical cells,”
she said. “So this may just be a rodent phenomenon.”
The loss of neurons is also a necessary part of brain development, she
“We always think that having more neurons is better, and it might
not be,” Juraska said. In some stages of early child development
up to half of the neurons in some brain regions are lost. The pruning
away of unneeded or disruptive neural circuits appears to be as important
to development as the growing of new neural connections, Juraska said.
Although other researchers had seen reductions in the size of the cortex,
“no one thought neurons were lost, unless some terrible thing
were happening,” Juraska said. “Now we are seeing that some
major changes are occurring in adolescence that no one has suspected.”
Juraska is in the Neuroscience Program and is an affiliate of the Beckman
Editor’s note: To reach Janice Juraska,
call 217-333-8546; e-mail: firstname.lastname@example.org.