Brain Network Maps Provide Insights into Mental Decline in Old Age

The human brain functions as a highly interconnected small-world network, not as an assortment of distinct regions as previously thought, with significant implications for the reason many people experience cognitive decline in old age. Australian researchers have mapped the brain's neural networks, and for the first time linked them with specific cognitive functions, such as information processing and language.

The study's findings were published January 26, 2011, in the Journal of Neuroscience. The researchers, from the University of New South Wales (UNSW; Sydney, Australia), are now looking at what factors may influence the efficiency of these networks in the hope they can be engineered to reduce age-related decline. "While particular brain regions are important for specific functions, the capacity of information flow within and between regions is also crucial,” said study leader Prof. Perminder Sachdev from UNSW's School of Psychiatry. "We all know what happens when road or phone networks get clogged or interrupted. It's much the same in the brain. With age, the brain network deteriorates and this leads to slowing of the speed of information processing, which has the potential to impact on other cognitive functions.”

The development of new magnetic resonance imaging (MRI) technology and increased computational power had allowed the development of the neural maps, resulting in a paradigm shift in the way scientists see the brain, according to Prof. Sachdev. "In the past when people looked at the brain they focused on the grey matter in specific regions because they thought that was where the activity was. White matter was the poor cousin. But white matter is what connects one brain region to another and without the connections grey matter is useless,” he said.

In the study, the researchers performed MRI scans on 342 healthy individuals aged 72 to 92, using an imaging technique called diffusion tensor imaging (DTI). Using a mathematical technique called graph theory, they plotted and measured the properties of the neural connectivity they observed. "We found that the efficiency of the whole brain network of cortical fiber connections had an influence on processing speed, visuospatial function--the ability to navigate in space--and executive function,” said study first author Dr. Wei Wen. "In particular greater processing speed was significantly correlated with better connectivity of nearly all the cortical regions of the brain.”

Prof. Sachdev reported that the findings help clarify how cognitive functions are organized in the brain, and the more highly distributed nature of some functions over others. "We are now examining the factors that affect age-related changes in brain network efficiency--whether they are genetic or environmental--with the hope that we can influence them to reduce age-related decline,” Prof. Sachdev concluded. "We know the brain is not immutable; that if we work on the plasticity in these networks we may be able to improve the efficiency of the connections and therefore cognitive functions.”

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University of New South Wales