Girls' brains reorganize earlier, may explain their faster maturity

Date: Dec-26-2013As we grow older, our brains reorganize themselves, pruning and

streamlining nerve fiber linkages to reduce overall network connectivity while selectively preserving long-distance connections that are crucial to information integration.

Now, a team led by Newcastle University in the UK has found this brain streamlining starts

earlier in girls, suggesting it may explain why they mature before boys in their teen years.

The researchers also suggest this gradual, selective reduction of connections may be the reason

brain function does not deteriorate - it even improves - during network pruning.

One of the study leaders, Dr. Marcus Kaiser, reader in Neuroinformatics at Newcastle, says:

"Long-distance connections are difficult to establish and maintain but are crucial for fast and

efficient processing."

Long-distance connections bring new information

To explain the value of the long-distance connection, Dr. Kaiser uses the idea of social networks:

"If you think about a social network, nearby friends might give you very similar information -

you might hear the same news from different people. People from different cities or countries are

more likely to give you novel information."

"In the same way, some information flow within a brain module might be redundant whereas

information from other modules, say integrating the optical information about a face with the

acoustic information of a voice, is vital in making sense of the outside world."

Short-cuts linking processing modules preserved

Researchers say they found that brain streamlining starts earlier in girls, potentially explaining why they mature before boys in their teen years.

For their study, researchers at Newcastle, Glasgow and Seoul Universities evaluated brain scans

of 121 healthy individuals aged between 4 and 40. They picked this age range because these are the

years when the major pruning of connections occurs.

The scans were done using a highly sensitive form of magnetic resonance imaging (MRI) known as

diffusion tensor imaging (DTI), which tracks water traveling along nerve fibers.

The DTI scans showed that the age range 4 to 40 was indeed a period when the brain was busy

pruning fibers.

However, the researchers found that in the case of long-range connections - called projections -

selective pruning was going on, and some types were pruned more heavily than others.

The projections that tended to be preferentially preserved were short-cuts that link different

processing modules and allow fast information transfer and synchronous processing. Examples

include connections between vision and sound modules.

The researchers say changes in these connections have been linked to developmental brain

disorders, such as epilepsy, autism and schizophrenia.

The social network analogy also serves to explain why reducing some projections in the brain

helps to focus on essential information. For instance, if you are lost and need to find your way,

instead of talking to lots of people at random, it is best to speak to a select few who have been

in the neighborhood a while.

First study to show loss of white matter is highly selective

With this study, the researchers have shown for the first time that the loss of white matter

fibers between brain regions is a highly selective process - one that they call preferential

detachment.

They found reduction in brain connections between distant regions, between hemispheres, and

between processing modules were fewer during brain maturation than expected, and they conclude

this may explain how the brain maintains a stable network as it matures.

The study, which forms part of the Human Green Brain project that is examining human brain

development, was funded by the British Engineering and Physical Sciences Research Council

(EPSRC).

Meanwhile, another team in the US published a study recently in the Proceedings of the

National Academy of Sciences that showed striking differences in brain wiring between men

and women.

In that study, researchers at the University of Pennsylvania also used DTI to reveal that in one

brain region, women have more connections between left and right hemispheres, and men within

hemispheres, while in another brain region, the pattern is the other way around.

Written by Catharine Paddock PhD

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