HOW TO GROW LONG IN THE TOOTH

13/11/06. By Lisa Melton

The Scottish Mental Surveys of 1932 and 1947.

In a nutshell

In 1932 and 1947, all 11-year-old Scottish schoolchildren took IQ tests.

By tracking down the original participants, researchers are tracing how people's mental abilities have changed over 60–70 years.

IQ is remarkably stable across lifespan, but how well the brain ages is influenced by mental and physical activity, genes, diet and disease.

People with lower IQs tend to die younger than those with higher IQs.

There are cardboard boxes stuffed with junk in cellars the world over. So Scottish scientists Ian Deary and Lawrence Whalley could never have imagined that boxes locked for nearly 60 years in a safe bunker in Edinburgh would contain the results of a survey of almost 88 000 children: the Scottish Mental Survey of 1932. By tracking down and retesting some of the original participants, they are shedding light on key factors that influence how well our brains age.

The rediscovery of the Scottish Mental Survey of 1932, long forgotten by everyone in the field, owes as much to luck as to friendship. Lawrence Whalley, Professor of Mental Health at the University of Aberdeen, had been given hundreds of yellowing growth charts of undernourished Scottish children born in 1921. This was potentially exciting, but the group had been poorly selected by a professor in anatomy with an interest in eugenics. Professor Whalley decided against pursuing this study.

Nonetheless, he mentioned these old files to his close collaborator Ian Deary, Professor of Differential Psychology at the University of Edinburgh, who was intrigued by one thing: the year in which those children had been born. It was 1921. Finally it clicked. In 1932, all 87 498 Scottish children born in 1921 had participated in a massive IQ survey, conducted by the Scottish Council for Research in Education (SCRE), as part of a drive to understand the nation's mental ability.

The children answered questions of verbal reasoning and numerical, spatial and abstract items. The 1932 Scottish Mental Survey was extraordinary in its scope, yet the data had not been seen or talked about in ages. Did the files still exist?

Professor Whalley tracked them down to a cement bunker in the SCRE's offices in St John Street, Edinburgh. The ledgers and parcels of brown paper tied with string, recorded in copperplate writing, had been preserved intact for nearly 60 years. "This will change our lives," Professor Deary remarked on hearing about the discovery.

What had happened to the brains of the original participants since 1932? They had celebrated more than half a century of experiences and lived through retirement; they might have suffered brain injury, intoxication, learned to play chess or returned to work – a lifetime of cognitive change.

To find out, Professors Deary and Whalley set out to track down some of the original volunteers, now in their late 70s, to invite them to sit the same intelligence tests they took all those years ago.

Local health registers were consulted to track down those men and women who took part in the Scottish Mental Survey of 1932. By 2001, the researchers had traced and retested over 700 of the children who sat those tests: over 230 in Aberdeen and about 550 in Edinburgh.

As well as retaking the original test, the participants were invited to attend the Wellcome Trust Clinical Research Facility in Edinburgh or the Medical School in the University of Aberdeen. Both of these are clinical centres equipped to collect medical data and samples, and perform electrocardiograms and breathing tests. Mental speed tests, hearing tests and in-depth investigations of family histories, social backgrounds, lifestyles, education, demographics, diets and health-related behaviours were all part of the visit. Some of the volunteers also had their brains scanned using magnetic resonance imaging.

Age does not treat everyone equally: some people hold steady or even improve their thinking skills, while the cognitive abilities of others decline with age. The rich array of data collected in Aberdeen and Edinburgh is allowing the researchers to probe the genetic influences and identify the environmental pressures that shape the ageing brain in different individuals.

"Knowing the childhood intelligence [of these elderly individuals] gives us the baseline from where to estimate the rate of change," Professor Whalley points out. The Scottish Mental Survey of 1932 provides those valuable early test scores. "That's unique, nobody else has that measure." What's more, the SCRE repeated exactly the same test 15 years later, when on 4 June 1947 it tested over 70 000 children all born in 1936 and at school that day.

Pump it up

While much of cognitive ageing is linked to disease, there are marked differences in normal brain ageing too. IQ is remarkably stable across the lifespan – "If I know their cognitive ability in youth, I've explained 50 per cent of how that group got to their cognitive levels in old age," says Professor Deary – but people with relatively similar mental abilities aged 11 don't always end up with similar abilities aged 80. The researchers observed that some manage to significantly increase their relative IQ standing, proof that it is possible to rack up brainpower beyond childhood potential with mental activity. "Something is pushing them up from where you'd expect them to be based on their childhood ability," he adds.

That something is likely to include education and social class. Educated people have an extra cognitive power that can protect against Alzheimer's disease. People in professional occupations, with a good education and high on the socioeconomic ladder, are more likely than others to reach a ripe old age in relatively good health.

It's never too late to fight senility, the survey results suggest. Keeping active – mentally and physically – through brain-stimulating activities such as puzzles, draughts or dancing lowers the risks of dementia and keeps normal ageing at bay. It's possible then, to boost the brain's 'cognitive reserve' and stop the cognitive decline of old age.

Hardware hits

The brain's hardware matters too. The main processing in the brain occurs in the grey matter, but the areas of grey matter must be connected up and allowed to talk to each other. This is the crucial role of the white matter, which needs to be intact for quick and accurate thinking.

The brain scans of elderly individuals reveal small, bright scar-like areas in the white matter. These lesions are a normal part of ageing, but after the age of 60, the more scarred the white matter, the poorer the mental abilities. "If you take two people who start at the same IQ level when they are young, the one whose white matter is less intact when they are old will, on average, be cognitively worse off," says Professor Deary.

It seems sensible, then, to avoid the insults. White matter is thought to be damaged by circulatory problems, including high blood pressure, diabetes, heart disease, cardiovascular risk factors and sleep apnoea. It looks as though what is bad for a person's cardiovascular system is also bad for the head.

Genes can also speed up cognitive ageing, and Professor Deary is keen to identify them. His aim, as part of the Genes to Cognition (G2C) neuroscience programme led by Professor Seth Grant at the Wellcome Trust Sanger Institute, is to find some of the genetic variations that lead to individual differences in cognition as people grow older.

It already appears that if a person has the E4 allele of the gene for apolipoprotein E (ApoE4, a genetic variant that increases the risk of Alzheimer's disease), mental capabilities will deteriorate more rapidly with age. But the size of the effect is small, perhaps just over 1 per cent of the variability of cognitive ageing. Using DNA chips or microarrays to scan hundreds of genetic targets at a time, the research team can build up each volunteer's genetic profile, track the impact of genes on the memory, learning and behaviour of ageing individuals, and tease apart the influence of socioeconomic factors. They aim to identify the impact of individual variations in genes that are thought to be involved in memory, intelligence, dementia, longevity and oxidative stress. The chances are that they will find many genetic factors chipping in, each of which will form only a small part of the variation in cognitive ageing.

Professor Deary is keen to stress, however, that links between a person's cognitive ageing and genetics are not necessarily unchangeable. "Once we know the genes, and the mechanisms that contribute to cognitive ageing, then they become a target for intervention," he says.

Beyond genes

The Scottish Mental Survey shows that where we end up, cognitively speaking, aged 70 depends partly on our childhood intelligence. What accounts for the rest? "Beyond genetics and white matter, we are looking at lifestyle factors," Professor Deary points out.

It is clear is that smoking is detrimental to cognition, for instance. Smokers age faster than people who have never smoked or who kicked the habit. "What we are gaining is a menu for successful ageing," says Professor Deary. "If people smoke, if they have certain types of genes, a mentally demanding job, high status and more education, we can explain in part why they reach their cognitive level."

And then there's diet. "For us, the top nutritional factor is homocysteine," says Professor Whalley, who has found that a build-up in this amino acid is linked to dementia. To keep the levels of homocysteine down, older people must ensure they consume enough vitamin B12 and folate. These two nutrients, which are normally absorbed from food, convert homocysteine to methionine; when they are in short supply, homocysteine levels shoot up. This happens more past the age of 50, when vitamin B12 and folate are no longer absorbed as efficiently. As a result, homocysteine accumulates in the body.

In which case, a fairly simple improvement in the diet could perhaps fend off some cognitive decline. "Vitamin B12 and folate, and their impact on homocysteine, appear to be the single most important nutritional factor; omega-3 fatty acids – found in oily fish and other foods – play a less important role," Professor Whalley notes.

Think fast

Of all the intriguing facts uncovered by the Scottish Mental Surveys, one stands out: intelligence can predict mortality. "Whether you live to collect your old-age pension depends in part on your childhood IQ scores," says Professor Deary. "There is a mysterious association between childhood IQ and death." People with lower IQs tend to die younger than those with higher IQs. But why? How can a mental test taken decades before death predict mortality?

Some scientists are not surprised that intelligent children have a gift for longevity. They argue that intelligence affects every aspect of a person's life – high IQ in childhood is likely to lead to educational success, placement into a well-paid job, higher social status and better use of healthcare facilities. Brighter people are more likely to understand and respond to health messages, and adopt a healthy lifestyle such as not smoking, controlling alcohol intake, eating a good diet and exercising.

Professor Deary is investigating an alternative explanation: "Maybe a childhood IQ is an indicator of how well the body is wired up." To look at this idea, he and Geoff Der (of the Medical Research Council Social and Public Health Sciences Unit in Glasgow) examined data from men and women aged 54–58 years old living in west Scotland who, back in 1988, had taken an IQ test and a reaction-time test that measured how quickly they pressed a button after seeing a number on a screen.

Over the next 14 years, 185 participants died, and Deary and Der compared the test results to see if the IQ or reaction time scores predicted mortality. Those with higher IQs lived longer – that much was expected. But they found something new: faster reaction times seemed to be a better predictor of a long life than IQ, perhaps indicating a well-built body. Smarter people's brains run faster, and their bodies age better than those with lower IQs (who tend to die younger). This 'system integrity' provides an intriguing possible explanation, which the scientists are keen to explore.

In a society faced with an ageing population, in which dementia, Alzheimer's disease and Parkinson's disease are bound to become more common, people need to do all they can to avoid mental decline. Now the formula for a sprightly old age is out of the box and is taking shape, thanks to those Scottish children and their carefully stored test results.

Lisa Melton is a science writer based in London.