What do we mean when we say someone is intelligent and is there any scientific basis for defining intelligence? These questions have been at the center of a more than century-old debate in psychology. Intelligence is, first and foremost, a judgment. He’s intelligent, he’s not intelligent, those are quick ways of saying that some behaviors of an individual observed in the past somehow predict how brilliant his next actions will be. Intelligence is an estimate of the quality that we attribute to the decision-making and abstract thinking of people around us. Although it may be practical for people to think of intelligence as something that exists, whether science should consider intelligence and how it would define it remains very controversial.
There are, in short, two types of theories of intelligence. You can either believe that there is a single factor of intelligence that determines the level of ability that we have in any task – a theory put forward by Charles Spearman who hypothesized that each individual might have a g factor, a general intelligence factor. This intelligence factor would make people better at tasks that are apparently unrelated and likely demand very different cognitive abilities. The second set of theories of intelligence stipulate that intelligence is divided in distinct categories; people would have specific ease with tasks of a particular domain and there would be no single factor explaining performance across different domains of intelligence.
A recent study published by Hampshire et al.1 from the University of Western Ontario has looked into the brain areas that are activated by tasks that are typically used to test for intelligence. In doing so they hoped to determine if brain areas related to cognitive demands are activated altogether as demands increase during intelligence tests of various kinds, or if some areas were activated during tests for a specific intelligence domain and not for others.
The study is thorough. They made subjects pass 12 tests that challenge intelligence in different manners. One test involves mapping words and colors together, some tasks are geometrical and others involve spatial reasoning. They were interested in the brain activities in a set of areas that they refer to as the multiple demand cortex, which is really a set of areas that seem to be activated by a broad range of tasks.
Using functional magnetic resonance imaging (fMRI), which provides a measure of blood oxygenation levels, they visualized the brain areas that are more or less activated by each of these tasks. What comes out of these experiments is that the whole set of brain regions they looked at is not uniformly activated by every task but that some areas are more activated during specific sets of tasks. They then defined 3 groups of tasks that seem to activate specific groups of brain areas: the short-term memory tasks, the reasoning tasks and the verbal tasks.
The study is interesting because it provides three candidate intelligence factors (instead of 1) that have been built not from intuition about what tasks do but based on the set of brain areas that might contribute to those tasks. However don’t get too excited, the methods used have severe limitations and we are still only at the hypothesis level. We do not know how these areas contribute to performance in intelligence tests and we do not know why they are activated and how they interact together to create the behavior.
1. Hampshire A, Highfield RR, Parkin BL, Owen AM. (2012) Fractionating human intelligence. Neuron 76:1225-1237.