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 said.
"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."
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Contact: Diana Yates
diya@uiuc.edu
217-333-5802
University of Illinois at Urbana-Champaign
13-Mar-2007