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Bigger is better when it comes to brain matter, says a leading neuroscientist.

Canadian researchers examined the brains of 100 people who were given extensive IQ tests before they died and found a correlation between cerebral volume and intelligence.

“This is essentially the first study that is actually looking at the size of the brain directly and not through imaging,” Sandra Witelson, who headed the study at the Michael G. DeGroote School of Medicine at McMaster University, said Thursday from Hamilton.

“What is very clear is that there is a correlation between brain size and intelligence, particularly verbal ability,” said Dr. Witelson, noting that verbal ability encompasses comprehension of complex sentences, understanding verbal logical information and verbal memory.

The study looked specifically at the size of the cerebrum, the thinking part of the brain, and found a correlation with verbal intelligence in women. The same correlation was found for right-handed men.

The research paper was published online this month by the journal Brain.

Dr. Witelson is the scientist who made headlines in 1999 after painstakingly studying the brain of the scientific genius Albert Einstein. She discovered that one part of his brain — the inferior parietal region, which is related to mathematical reasoning — was 15 per cent wider on both sides than normal.

Her latest study involved the brains of 58 women and 42 men who all lived and died in the Hamilton area over the past 25 years. The subjects had secondary stage cancers — their cancers had spread, or metastasized — and while still relatively healthy, they agreed to take the intelligence tests as well as donate their brains to science after death.

Some studies have looked at intelligence using MRI images of the brain, but Dr. Witelson noted there is room for ambiguity in the images that come through computer programs.

Likewise, she said people can't just look at head size and determine that a smaller head means a smaller brain, or vice versa. “There's a lot inside a skull other than just the brain,” she said.

The brains in her study were weighed and the volume calculated through the simple Archimedes' principle — they were placed in water, and measures were taken of how much water was displaced.

The individuals had also been tested for spatial thinking skills, which would include doing block designs and putting pieces together to make a puzzle.

Spatial intelligence was also correlated with brain size in women, the researchers found.

“But the relationship was not as strong,” Dr. Witelson said. “But the point is, in women, whether it was verbal or non-verbal intelligence, brain size was positively correlated — that means the bigger the brain, the better they did.”

In men, visual-spatial intelligence was not related to overall brain size.

Previous research found that Einstein's overall brain was a normal size, she noted, but the specific portion known for spatial intelligence was wider and had a unique anatomy.

“What we're suggesting, and this remains to be tested by further work, that in men it isn't the size of the overall brain that is correlated with how well they do on all these mazes and three-dimensional perception tests, but it might be the structure, it might be the size or the anatomical microscopic structure of the region in the brain that is important for that kind of thinking,” Dr. Witelson said.

She also found that brain size decreased in men over the years — from age 25 to 80 — but age hardly affected brain size in women.

The study was funded by the U.S. National Institutes of Health, the Canadian Institutes of Health Research and the Albert Einstein/Irving Zucker Chair in Neuroscience at McMaster University.