Brain Size Matters Little

When it comes to our gray matter, bigger doesn't mean smarter

Big brains mean big smarts, right?

Not so, according to a new study from the University of Vienna.

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Brain size plays just a minor role in determining intelligence, the study has found. An international team of researchers studied 148 neuro-imaging samples from more than 8,000 participants and found only weak associations between brain volume and IQ.

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“The presently observed association means that brain volume plays only a minor role in explaining IQ test performance in humans,” Jakob Pietschnig, professor of applied psychology at the University of Vienna, said in a statement about the research.

“Although a certain association is observable, brain volume appears to be of only little practice relevance. Rather, brain structure and integrity appear to be more important as a biological foundation of IQ.”

In humans, the brain sizes — just like body sizes — of men are overall larger than the brain sizes of women. But the disparity in size does not yield higher IQ scores across the genders.

What about across the animal kingdom?

If you’re looking for largest brain-to-body mass ratio, the shrew (a small, mole-like animal) wins easily with a brain that averages 1.3 grams, which amounts to 9 percent of its total weight.

By contrast, the sperm whale’s 20-pound brain is only 0.06 percent of its total body weight, which comes to 32,000 pounds.

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The bottlenose dolphin’s 3.5 pound brain amounts to 0.2 percent of body weight. Orcas — some of the smartest marine mammals — have brains that are only 0.07 percent of their total weight. And gorillas have brains that are about 0.3 percent of their average adult body weight.

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Homo sapiens don’t rank at the top of any brain size lists, including those lists that compare brain weight with body mass ratio. The average adult human has a brain that weighs about 3 pounds, which is about 2 percent of body weight for a normal person.

And as we keep growing larger and fatter, that ratio shrinks.

But the folklore that brain size equals intelligence probably isn’t disappearing anytime soon.

Rumors abound that a posthumous examination of Albert Einstein’s brain showed that he had an abnormally large one. Turns out the rumors are true. But Einstein’s brain differed from other scientists’ brains in that it had a higher ratio of fatty glial cells to neurons. Scientists have yet to examine his brain for the structural connections between the cells.

The true indicator of greater intelligence is synaptic plasticity, which has to do with how neurons communicate.

Increasingly, scientific evidence suggests the real genetic indicator of greater intelligence is synaptic plasticity, which has to do with how neurons communicate. The thickness of your cerebral cortex — the area that plays a role in memory, language, and consciousness — also correlates with intellect.

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Even healthy human brains shrink slightly as they age. Older adults sometimes have difficulty retaining and retrieving information because their prefrontal cortex has shrunk. However, if given enough time to complete a memory test, most people in their 70s and 80s often score as high as young adults do. And as you age, you can also expect to improve in other cognitive areas, such as vocabulary and verbal communication.

Bottom line: Bigger brains don’t amount to a hill of beans. The recipe for real smarts isn’t rocket science. Maintaining a healthy weight, exercise, minimizing alcohol (particularly binge drinking), eating more fruit and vegetables, and keeping mentally and socially active are your best bets for protecting that gray matter through your golden years.

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