Intelligence isn’t a single process – but it still depends on the coordinated activity of some specific brain areas, a new study reports.
In one of the most sweeping surveys in neuroscience history, researchers put patients with various types of brain damage through a battery of cognitive tests, and pinpointed the neural correlates of “general intelligence” to a few areas of the left hemisphere – and the connections among them.
This research brings up two topics that’ve been hotly debated since the early days of brain research: 1) what exactly we mean when we say “intelligence,” and 2) what exactly it is about the brain that allows us to think intelligently.
In ancient Roman and medieval times, the word “intelligence” was pretty much synonymous with “understanding” – the Latin intellectus and the Greek νοῦς (nous) were both often translated as “intellect” or “mind.” Needless to say, these aren’t very specific terms – which is why, by the mid-19th century, thinkers like Francis Galton had begun to use the term more precisely, to denote skill at problem solving, especially of cognitively complex tasks.
Ironically enough, it was Galton’s own intelligence quotient (IQ) tests that revealed a fatal flaw in any hard-and-fast definition of intellect: intelligence never seems to work exactly the same way in any two brains. This has led to a whole plethora of intelligence sub-types – such as “verbal comprehension” and “processing speed” – that modern IQ tests try to factor in.
Today, the WAIS-III and the D-KEFS are two of the most widely used intelligence tests in clinical settings (such as cases of brain-damaged patients) and both tests evaluate a variety of skills, from vocabulary to abstract reasoning to pattern recognition.
These tests provided a framework for a team led by Aron Barbey at the University of Illinois to look for correlations between certain kinds of intelligence oddities and certain kinds of brain damage, the journal Brain reports.
The team gathered a pool of 182 Vietnam veterans, all with highly localized brain damage due to combat injuries, and ran them through the gauntlet of both intelligence tests. Whereas, say, a stroke or Alzheimer’s disease often damages many areas of the brain, these patients’ localized injuries – mapped on the latest CT-scanning technology – gave the researchers very specific data on which brain areas were necessary for which aspects of intellect.
The team discovered something rather unexpected: many types of intelligence depend on the same few brain regions – and on the connections that unite them:
Impaired performance on these measures was associated with damage to a distributed network of left lateralized brain areas, including regions of frontal and parietal cortex and white matter association tracts, which bind these areas into a coordinated system.
In other words, intellect isn’t just a function of the frontal lobe – it also depends on the left parietal lobe, as well as on connective fibers of white matter that enable these areas to coordinate their activity. And as I’ve mentioned before, the right hemisphere undoubtedly has its own important part to play in this system.
The observed findings support an integrative framework for understanding the architecture of general intelligence and executive function, supporting their reliance upon a shared fronto-parietal network.
This confirms that our brain’s structural networks are the “hardware” that keeps the “software” of our functional networks running – and that without those functional networks, our brain wouldn’t be able to sustain such consistent patterns of complex activity across a person’s entire lifetime.
And this is great news, because our brains are constantly making new neurons, pruning away unused connections, and organizing themselves more efficiently – which means that the more we put that left-hemispheric network to use, the better it’ll get at doing its many jobs.
In short, even if you’re no Daniel Tammett, you can still look forward to a lifetime of growing smarter. And that’s a fact worth understanding.
The Connectome 