Healthy Brain Connections Keep Us Smart In Old Age
This brain "wiring" or white matter comprises billions of nerve fibers that carry signals around the various parts of the brain, and its condition affects our intelligence, for instance by influencing processing speed, conclude University of Edinburgh researchers in a study funded by the charity Age UK.
The study found that older people with "robust brain wiring", or whose white matter is in good condition, can process information quickly, which, the researchers suggest, boosts intelligence.
"Here, we provide evidence that lower brain-wide white matter tract integrity exerts a substantial negative effect on general intelligence through reduced information-processing speed," they write.
According to the findings, linking distant regions of the brain with healthy wiring improves mental performance, supporting the idea that intelligence is not found in one part of the brain.
The study forms part of a large research project led by Professor Ian Deary called Disconnected Mind, which aims to discover mechanisms of cognitive ageing. Deary also heads the Centre for Cognitive Ageing and Cognitive Epidemiology at Edinburgh.
This study is thought to be the first to show that deterioration of white matter as we get older is a significant cause of age-related cognitive decline.
For their investigation, first author Dr Lars Penke and colleagues acquired structural brain magnetic resonance imaging scans from 420 older adults in their early 70s. The participants were part of the Lothian Birth Cohort of 1936, a group of nearly 1,100 people whose intelligence and general health have been followed since the age of 11.
From the scans the researchers were able to measure three properties: "fractional anisotropy" and two white matter integrity biomarkers that have not been used before to study intelligence: "longitudinal relaxation time" and "magnetisation transfer ratio".
Together, these properties measure the amount of water in brain tissue, indicate structural loss in the brain, and how well the nerve fibres are insulated.
As well as these scan measurements, as measures of intelligence, the researchers also had data from thinking and reaction time tests that the participants had completed.
The results showed that each of the three white matter properties they measured "was independently associated with general intelligence, together explaining 10% of the variance, and their effect was completely mediated by information-processing speed".
Penke, who lectures in psychology, and whose main research interest is in biological foundations of individual differences, said in a statement:
"Our results suggest a first plausible way how brain structure differences lead to higher intelligence. The results are exciting for our understanding of human intelligence differences at all ages."
"They also suggest a clear target for seeking treatment for mental difficulties, be they pathological or age-related. That the brain's nerve connections tend to stay the same throughout the brain means we can now look at factors that affect the overall condition of the brain, like its blood supply," he added.
Having established the importance of brain connections, the team is now looking at what keeps the connections healthy.
"We value our thinking skills, and research should address how we might retain them or slow their decline with age."
Professor James Goodwin, Head of Research at Age UK, said by improving our understanding of how the brain works we can find out "why mental faculties decline with age in some people and not others and look at what can be done to improve our minds' chances of ageing better".
Written by Catharine Paddock PhD