As we age, our brains undergo a major reorganization, a 'pruning' which streamlines the connections in the brain - except the long-distance ones that are crucial for integrating information.
Studying people up to the age of 40, authors of a paper
in Cerebral Cortex suspect this newly-discovered selective process might explain why brain function does not deteriorate – and indeed improves –during this pruning of the network. Interestingly, they also found that these changes occurred earlier in females than in males.
The researchers evaluated the scans of 121 healthy participants between the ages of 4 and 40 years as this is where the major connectivity changes can be seen during this period of maturation and improvement in the brain. Using diffusion tensor imaging, a measurement protocol for Magnetic Resonance Imaging (MRI) scanners, they demonstrated that fibers are overall getting pruned that period.
However, they found that not all projections (long-range connections) between brain regions are affected to the same extent; changes were influenced differently depending on the types of connections.
Projections that are preserved were short-cuts that quickly link different processing modules, e.g. 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 have demonstrated for the first time that the loss of white matter fibres between brain regions is a highly selective process – a phenomenon they call preferential detachment. They show that connections between distant brain regions, between brain hemispheres, and between processing modules lose fewer nerve fibres during brain maturation than expected. The researchers say this may explain how we retain a stable brain network during brain maturation.
Co-author Dr. Marcus Kaiser of Newcastle University explains, "Long-distance connections are difficult to establish and maintain but are crucial for fast and efficient processing. 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."