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Earlier brain “pruning” may explain girls’ faster maturation

Dec. 19, 2013
Courtesy of Newcastle University
and World Science staff

The brain re-organizes its con­nec­tions through­out life, but the pro­cess be­gins ear­li­er in girls, which may ex­plain why they ma­ture faster in their teens, sci­en­tists have found.

As we grow old­er, our brains un­dergo a ma­jor re­or­gan­iz­a­tion, re­duc­ing the con­nec­tions among brain cells. Sci­en­tists led by Mar­cus Kai­ser and Sol Lim at New­cas­tle Uni­vers­ity in the U.K. found that while over­all con­nec­tions get stream­lined, long-dis­tance con­nec­tions cru­cial for in­te­grat­ing in­forma­t­ion are pre­served.

Map of brain con­nec­tions in a four-year-old boy. Col­ors rep­re­sent the lo­cal di­rec­tions of a fi­ber tract (blue: top-bot­tom; green: front-back; red: left-right). (Cour­te­sy New­cas­tle U.)


The re­search­ers sus­pect this might ex­plain why brain func­tion does­n’t de­cline, but rath­er im­proves dur­ing this “prun­ing” of the brain net­work. They al­so found that the changes oc­curred ear­li­er in fe­males.

“Long-distance con­nec­tions are dif­fi­cult to es­tab­lish and main­tain but are cru­cial for fast and ef­fi­cient pro­cessing,” Kai­ser said. “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.”

That could ex­plain why far-away con­nec­tions are of­ten more im­por­tant than closer-by ones among nerve cells that car­ry in­forma­t­ion through the brain, he added.

The re­search­ers stud­ied brain scans of 121 peo­ple be­tween four and 40 years of age, the pe­ri­od most as­so­ci­at­ed with the con­nec­ti­vity changes. They used a non-invasive tech­nique called dif­fu­sion ten­sor im­ag­ing – which is based on the more widely known Mag­net­ic Res­o­nance Im­ag­ing.

The sci­en­tists found that the changes were in­flu­enced dif­fer­ently de­pend­ing on the types of con­nec­tions.

Links that are pre­served were found to be short cuts that quickly link dif­fer­ent pro­cessing “mod­ules,” such as for vi­sion and sound, and al­low fast in­forma­t­ion trans­fer and syn­chro­nous pro­cessing. Changes in these con­nec­tions have been found in many de­vel­op­men­tal brain dis­or­ders in­clud­ing au­tism, ep­i­lep­sy and schiz­o­phre­nia, the re­search­ers said.

“The loss of con­nec­ti­vity dur­ing brain de­vel­op­ment can ac­tu­ally help to im­prove brain func­tion by re­or­ganizing the net­work more ef­fi­ciently. Say in­stead of talk­ing to many peo­ple at ran­dom, ask­ing a cou­ple of peo­ple who have lived in the ar­ea for a long time is the most ef­fi­cient way to know your way. In a si­m­i­lar way, re­duc­ing some pro­jec­tions in the brain helps to fo­cus on es­sen­tial in­forma­t­ion,” Lim said.


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The brain re-organizes its connections throughout life, but the process begins earlier in girls, which may explain why they mature faster in their teens, scientists have found. As we grow older, our brains undergo a major reorganization, reducing the connections among brain cells. Scientists led by Marcus Kaiser and Sol Lim at Newcastle University in the U.K. found that while overall connections get streamlined, long-distance connections crucial for integrating information are preserved. The researchers suspect this might explain why brain function doesn’t decline, but rather improves during this “pruning” of the brain network. They also found that the changes occurred earlier in females. “Long-distance connections are difficult to establish and maintain but are crucial for fast and efficient processing,” Kaiser said. “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.” That could explain why far-away connections are often more important than closer-by ones among nerve cells that carry information through the brain, he added. The researchers studied brain scans of 121 people between the ages of 4 and 40 years, the period most associated with the connectivity changes. They used a non-invasive technique called diffusion tensor imaging – which is based on the more widely known Magnetic Resonance Imaging. The scientists found that the changes were influenced differently depending on the types of connections. Links that are preserved were found to be short cuts that quickly link different processing “modules,” such as for vision and sound, and allow fast information transfer and synchronous processing. Changes in these connections have been found in many developmental brain disorders including autism, epilepsy and schizophrenia, the researchers said. “The loss of connectivity during brain development can actually help to improve brain function by reorganizing the network more efficiently. Say instead of talking to many people at random, asking a couple of people who have lived in the area for a long time is the most efficient way to know your way. In a similar way, reducing some projections in the brain helps to focus on essential information,” Lim said.