The definition of human intelligence from the Encyclopedia Britannica is: “mental quality that consists of the abilities to learn from experience, adapt to new situations, understand and handle abstract concepts, and use knowledge to manipulate one’s environment”. The world of brain function and brain health has been turned on its ear over the past twenty years or so. When the understanding of neuroplasticity and neurogenesis became mainstream and initiated different paths of research, there was research that was spawned in the area of intelligence.
The Categories of Intelligence
More than seventy years ago, psychologist Raymond Cattell and his student John Horn put forth the proposal that intelligence was not one specific thing but instead was a collection of various abilities working together. This idea was called the Cattell-Horn theory which stated that these different abilities could be classified into two categories: fluid intelligence and crystallized intelligence. These two categories composed general intelligence. Fluid abilities allow a person to solve new problems and encode short-term memory. Crystallized abilities are born from knowledge and general information (K. Sukel, May 26, 2015). Cattell and Horn believed that both of these types of intelligence increased throughout childhood and adolescence. Fluid intelligence would peak in the early twenties but crystallized intelligence would go on and develop into the thirties and forties.
This had been the prevailing theory of intelligence for many decades. The overarching belief was that cognition couldn’t get any better after a certain age. Research in brain development centered on the premise that “the brain is mostly mature by 18 – and then there’s a little more maturation of the frontal lobe into your 20s. But once that happened, then, it was thought, you were done,” said Joshua Hartshome, a post-doctoral fellow at MIT. “So it fit with this idea that nothing was changing until older age.” And, in older age, cognitive decline was occurring. The discovery that the brain was far more plastic (malleable) than believed, researchers at MIT wondered if there was more to cognitive peaks across the lifespan than had formerly been investigated.
The Research on Fluid and Crystallized Intelligence
Fluid and crystallized intelligence do change throughout our lives, with certain mental abilities peaking at different points. Past research indicated that fluid intelligence peaked early in life but it has been discovered that certain aspects actually peak as late as age forty. Crystallized intelligence continues forward with a peak around age sixty or seventy. There is evidence to support that certain abilities peak at certain times. With this new understanding come new questions. What kinds of abilities are changing, why are they changing, and what’s driving those changes?
Where else does research in this field lead us? Researchers from Brisbane, Edinburgh, and Aberdeen revisited a study of 2000 people who had IQ tests in 1932 and 1947 and revealed that one-quarter of the participants’ change in intelligence was due to genetic factors. This study also revealed that the largest influence on changes in intelligence is environmental. These findings spurred researchers into looking at what are the roles of genetics and environmental factors in determining our intelligence and how it changes across peoples’ lifetimes (Science in Public, 2012). Studies over the years since early 2000, have shown that people who took intelligence tests as children and then again in old age, tended to keep about the same relative score. But, there was also some change: some who scored well in early tests went down a bit, and those who scored low early did better in old age. Now researchers want to know what drives these changes in lifetime cognitive aging (Science in Public, 2012).
The Effect of Genetics and Environment on Intelligence
Professor Peter Visscher from Queensland Brain Institute noted that “Identifying genetic influences on intelligence could help us 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.” Researchers went back to the participants tested for intelligence in 1932 and 1947 and were able to get DNA samples from approximately 2000 participants ranging from age sixty-five to seventy-nine. Scientists examined over a half a million genetic markers to work out how genetically similar the participants were, even though they were not related. Their results were not especially significant but did provide data that was never available before. Never before did they have information that gave an estimate of how much genetic differences affect intelligence changes across the lifetime. Professor Deary of the Edinburgh’s Centre for Cognitive Ageing and Cognitive Epidemiology states that “The results partly explain why some people’s brains age better than others”.
“This study also strongly suggests how important our environment is in helping us stay sharp as we age” states Professor 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 disease like dementia.”
References:
Cherry,K. (July 12, 2015). Fluid intelligence vs. crystallized intelligence. Retrieved March 3, 2016 from http://psychology.about.com/od/cognitivepsychology/a/fluid-crystal.htm
Human intelligence. Retrieved March 2, 2016 from http://www.britannica.com/print/article/289766
Science in Public (January 19, 2012). How does our intelligence change through life. Retrieved March 3, 2016 from http://www.scienceinpublic.com.au/other/how-does-our-intelligence-change-through-life
Sukel,K. (May 26,2015). Maturing intelligence. Retrieved March 2, 2016 from http://www.dana.org/News/Maturing_Intelligence/
