The Scottish Mental Surveys 17/11/04. By Giles Newton At the University of Edinburgh, Professor Ian Deary is investigating non-pathological cognitive ageing – the changes in mental abilities that come with age.

"A lot of cognitive ageing is linked to disease," says Professor Deary, " but we are studying normal cognitive ageing and how genetic differences affect cognitive domains in older people." He is also part of the Genes to Cognition project, which is investigating the genes that involved in memory, learning and behaviour.

Feature: Genes and cognition

Not all cognitive processes are affected equally by age: vocabulary and general knowledge do quite well, for example, but some aspects of memory, non-verbal reasoning, processing speed and other capabilities tend to deteriorate with age. But most researchers in this area are hampered by not having a baseline for comparison. Professor Deary provided an analogy with height. "We know that people tend to get a little shorter as they get older. But to study this, you need to know how tall people were when they were young. It's the same with the brain. We can examine people’s mental abilities when they are old, but studies are so much more powerful if we know their abilities when young."

Fortunately, such a resource exists: the Scottish Mental Surveys of 1932 and 1947. On 1 June 1932, 87 498 children born in 1921 took the same IQ test – an 11-plus-type test, 45 minutes long, that examined verbal, spatial, numerical and abstract reasoning. There were 71 questions, with a maximum score of 76 (no one scored 76 at age 11, but three people who took the test again, aged 80, did get the maximum). 15 years later, amid worries at that time that the nation's IQ was declining, the test was repeated: on 4 June 1947, 70 805 children born in 1936 were tested. In fact, contrary to their concerns, they found that the average score rose slightly.

"Scotland is the only place that has ever tested a complete nation for IQ," says Professor Deary. "We are interested in how people have changed with age, so we are recruiting people who took part in the 1932 survey, and who are now in their early 80s. For example, 200 people from Aberdeen, and 500 from Lothian have been involved already. They come to the Wellcome Trust Clinical Research Facility in Edinburgh, and we collect data on their cognitive phenotypes, education and social background, medical data, DNA, biochemistry, blood, ECGs, physiology and demographics."

What is clear is that people who start at age 11 with relatively similar IQs don't always end up with similar mental abilities at age 80 – even when you allow for health, lifestyle, demographics. Some age more successfully, others more quickly. Lifestyle certainly appears to influence cognitive ageing. Smokers decline faster than people who have never smoked or who gave up smoking, for example, while people in more professional occupations do rather better.

The effects of genetics are more difficult to tease apart, the only replicated effect to date being with ApoE4 (a genetic variant that is known to increase the risk of Alzheimer's disease). This seems to speed up cognitive ageing in the elderly, but only by a small amount. "The size of the effect is small, perhaps 1 per cent of the variability of cognitive ability," says Professor Deary, "so we're also looking at genes associated with dementias, cardiovascular disease, memory, intelligence, and oxidative stress to see if they influence normal cognitive ageing."

Image credit: Adrian Cousins