How does our intelligence change through life

Embargo 6 am AEST, Thursday 19 January 2012

Issued for the Queensland Brain Institute, University of Queensland.

Researchers from Brisbane, Edinburgh and Aberdeen have revisited about 2,000 people who had intelligence tests in 1932 or1947, and shown that genetic factors may account for about a quarter of the changes in intelligence over their lives.

The unique study also suggests that the largest influence on changes in intelligence is environmental.

It still remains for researchers to identify exactly which genes are involved, and this could contribute to understanding and ameliorating cognitive decline.

The latest paper is helping then to hone in on the causes of these changes, and on the underlying question of the roles of genetics and environmental factors in determining our intelligence and how it changes across people’s lifetimes.

In a number of studies since early 2000 the Edinburgh and Aberdeen researchers have shown that, when people took intelligence tests as children and then again in old age, they tended to keep about the same relative score. However, there was also some change: some who did well early on went down a bit, and some who scored poorly as children did better in old age. The researchers are keen to understand what drives these changes in lifetime cognitive ageing.

“Identifying genetic influences on intelligence could help us to understand the relationship between knowledge and problem solving and an individual’s outcomes in life, and especially to understand why some people age better than others in terms of intelligence,” says paper co-author Professor Peter Visscher, from the Queensland Brain Institute and the University of Queensland Diamantina Institute. “We excluded people with dementia.”

“This research was only possible because of remarkable detective work by Professor Ian Deary and his team at the University of Edinburgh, and Professor Whalley and his team at the University of Aberdeen,” he says.

In June 1932 and June 1947 intelligence tests were carried out on almost all children born in Scotland in 1921 and 1936, respectively. Ian Deary and colleagues successfully tracked down 2000 of these people who, then aged from 65 to 79, agreed to be re-tested and to give samples for DNA analysis.

The scientists then examined more than half a million genetic markers to work out how genetically similar the individuals were, even though they were not related.

“Until now, we have not had an estimate of how much genetic differences affect how intelligence changes across a lifetime,” says Professor Deary of the University of Edinburgh’s Centre for Cognitive Ageing and Cognitive Epidemiology. “The results partly explain why some people’s brains age better than others. We are careful to suggest that our estimates do not have conventional statistical significance, but they are nevertheless useful because such estimates have been unavailable to date.”

“The results also strongly suggest how important the environment is helping us to stay sharp as we age. Neither the specific genetic nor environmental factors were identified in this research. Our results provide the warrant for others and ourselves to search for those,” says Prof Visscher.  “It’s critical information because we know that intelligence is a predictor of many factors including lifespan, health, income. And, as our community ages we need to understand how we can predict and ultimately manage changes in cognitive thinking. Ultimately, understanding the influence of genetics in a healthy brain will help us understand and combat the changes caused by diseases like dementia.”

For the University of Queensland’s Queensland Brain Institute

Visit www.scienceinpublic.com.au for background and links to the paper.

For interviews contact Professor Peter Visscher, +61 7 3346 6348, peter.visscher@uq.edu.au

Or Niall Byrne on 0417 131 977, niall@scienceinpublic.com.au

For the University of Edinburgh

Joanne Morrison, Press and PR Office, +44 131 651 4266; email Joanne. Morrison@ed.ac.uk 

Background information

When looking at people’s intelligence (as measured by an intelligence test) early and late in life, people vary in how well they age cognitively. Some people are above average and remain that at old age, others decline relative to their intelligence in childhood, and yet others improve. We are trying to understand what explains these differences between people, in particular whether there are any genetic factors that explain some or all of the variation in cognitive ageing. We used a unique cohort of people in Scotland for which we have measures of intelligence over their entire life course.

It is known, from family and twin studies, that variation in intelligence at childhood and variation at old age is partly genetic. It is known from Professor Deary’s earlier studies that intelligence in childhood and old age are correlated so that, on average, people who are above average in childhood remain above average at old age. Not known is whether this observed correlation is due to genes or the environment. What was also not known is whether the heritability of intelligence that is inferred from twin studies can be confirmed using DNA data on unrelated people.

The key findings are that (i) we confirm, by using DNA data on unrelated people, that differences between people in intelligence in childhood and differences at old age is partly due to genes and (ii) we estimate that about one quarter of the change in intelligence from childhood to old age is due to genetic factors.

How well one ages cognitively depends both on your genes and your environment. Finding the genes may help to better understanding why some people decline cognitively and may give leads into a better understanding of the onset of dementia.  Identifying the environmental factors that improve healthy brain ageing is of benefit to all of us. Our study shows that it is worthwhile to look for both genetic and environmental clues to healthy brain ageing.

The paper

doi:10.1038/nature10781

Genetic contributions to stability and change in intelligence from childhood to old age

Ian J. Deary1,2*, Jian Yang3*, Gail Davies1,2, Sarah E. Harris2,4, Albert Tenesa4,5, David Liewald1,2, Michelle Luciano1,2, Lorna M. Lopez1,2, Alan J. Gow1,2, Janie Corley1, Paul Redmond1, Helen C. Fox6, Suzanne J. Rowe5, Paul Haggarty7, Geraldine McNeill6, Michael E. Goddard8, David J. Porteous2,4, Lawrence J. Whalley6, John M. Starr2,9 & Peter M. Visscher2,3,10,11*

1Department of Psychology, University of Edinburgh, 7 George Square, Edinburgh EH8 9JZ, UK.

2Centre for Cognitive Ageing and Cognitive Epidemiology, University of Edinburgh, 7 George Square, Edinburgh EH8 9JZ, UK.

3Queensland Institute of Medical Research, 300 Herston Road, Brisbane, Queensland 4006, Australia.

4Medical Genetics Section, Molecular Medicine Centre, Institute of Genetics and Molecular Medicine, Western General Hospital, Edinburgh EH4 2XU, UK.

5The Roslin Institute, Royal (Dick) School of Veterinary Studies, University of Edinburgh, Roslin, Edinburgh EH25 9RG, UK.

6Institute of Applied Health Sciences, Foresterhill, Aberdeen AB25 2ZD, UK.

7Nutrition and Epigenetics Group, Rowett Institute of Nutrition and Health, University of Aberdeen, Greenburn Road, Bucksburn,

Aberdeen AB21 9SB, UK.

8Department of Food and Agricultural Systems, University of Melbourne, Parkville, Victoria 3011, Australia and Victorian Department of Primary Industries, Bundoora, Victoria 3083, Australia.

9Alzheimer Scotland Dementia Research Centre, University of Edinburgh, 7 George Square, Edinburgh EH8 9JZ, UK.

10University of Queensland Diamantina Institute, University of Queensland, Princess Alexandra Hospital, Brisbane, Queensland 4102, Australia.

11The Queensland Brain Institute, The University of Queensland, Brisbane, Queensland 4072, Australia.

Understanding the determinants of healthy mental ageing is a priority for society today. So far, we know that intelligence differences show high stability from childhood to old age and there are estimates of the genetic contribution to intelligence at different ages. However, attempts to discover whether genetic causes contribute to differences in cognitive ageing have been relatively uninformative. Here we provide an estimate of the genetic and environmental contributions to stability and change in intelligence across most of the human lifetime. We used genome-wide single nucleotide polymorphism (SNP) data from 1,940 unrelated individuals whose intelligence was measured in childhood (age 11 years) and again in old age (age 65, 70 or 79 years). We use a statistical method that allows genetic (co)variance to be estimated from SNP data on unrelated individuals. We estimate that causal genetic variants in linkage disequilibrium with common SNPs account for 0.24 of the variation in cognitive ability change from childhood to old age. Using bivariate analysis, we estimate a genetic correlation between intelligence at age 11 years and in old age of 0.62. These estimates, derived from rarely available data on lifetime cognitive measures, warrant the search for genetic causes of cognitive stability and change.

Discovering the fundamental mechanisms of brain function

Researchers at the Queensland Brain Institute (QBI) work to discover the cellular and molecular mechanisms that underlie the ability of the adult brain to generate new nerve cells and form functional connections.

QBI is headed by Professor Perry F. Bartlett, ARC Federation Fellow, UQ Foundation Chair in Molecular Neuroscience and Fellow of the Australian Academy of Science.

Neuroscience is entering an era of accelerated discovery driven by the application of new molecular, genetic and imaging technologies, which will provide a deeper understanding of the regulation and function of the nervous system.

The Queensland Brain Institute (QBI) was established as a research institute of the University of Queensland in 2003. The Institute is now operating out of a new $63 million state-of-the-art facility and houses 27 Principal Investigators with strong international reputations. QBI is one of the largest neuroscience institutes in the world dedicated to understanding the mechanisms underlying brain function.