Where in the Brain is Intelligence?

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Where in the Brain is Intelligence?

From autopsies of famous Russians to a new model based on imaging studies, scientists keep looking



The blue circles mark brain areas in the left hemisphere strongly associated with intelligence and reasoning, while red circles mark relevant areas in both hemispheres. The P-FIT model proposes that those areas are linked by a neural pathway known as the arcuate fasciculus, represented by the arrow, which is vital for the production and comprehension of language. (image courtesy of Rex E. Jung and Richard J. Haier)

For years, Russian scientists harvested the brains of exceptionally smart people, trying to locate the source of their intelligence. After V.I. Lenin died in 1924, for example, the Russians invited the great German neuroanatomist Oskar Vogt to try to locate the “source of genius” in the leader of the Russian revolution. Vogt cut Lenin’s brain into more than 1,100 slices, but he found nothing exceptional except unusually large pyramidal cells.

The last brain that the Russians studied in this way was that of Andrei Sakharov, the nuclear physicist and human rights activist who died in 1989. From the dozens of brains they studied, the researchers made many observations about brain size, the density of neurons and the number of convolutions of the cortex, but their findings revealed next to nothing about human intelligence.

Today, scientists around the world continue to search for the physiological basis of human intelligence, but they also focus on genetic variation, which appears to determine about half of a brain’s cognitive ability on average, as measured by standard IQ tests. And by using modern scanning techniques, they are gaining much more detailed insights into the structure and function of the brain than the Russians could achieve through dissection.

The emerging consensus is that intelligence depends not just of the efficiency or power of various brain regions, but also on the strength of the connections that link them.

“These early attempts to find the physiological basis of intelligence were limited by a lack of modern technology,” said Richard J. Haier, a professor in the School of Medicine at the University of California, Irvine, who uses brain imaging to study higher cognitive processes. “With the advent of modern medical imaging it became possible to look for more subtle differences than you might find with gross anatomy.”

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