Unlike Women, Men Get More Stupid as They Get Older

Bigger is better when it comes to brain size. That's what numerous neurological studies on the correlation between intelligence and brain size have found. The most comprehensive such study so far has been published in the December issue of the journal Brain, a study which has also delved into questions regarding sex differences.

The team led by neuroscientist Sandra Witelson from the Michael G. DeGroote School of Medicine has provided some of the clearest evidence on how brain size changes in time and how it influences intelligence.
There are several types of intelligence, such as linguistic intelligence (the ability of using language), intra-personal intelligence (the ability to perceive and make distinctions in the moods, intentions, temperaments, and feelings of other people), bodily kinetic intelligence (the ability of coordination, balance, dexterity and flexibility), spatial intelligence (the ability to mentally rotate objects and to understand the components of visual and spatial displays within pictures and paintings) etc.

The team focused on linguistic intelligence and on spatial intelligence and determined the correlation between them and brain size.

The rather grim aspect of the study was that in order to determine brain size precisely it needed the brains. Thus, since 1977 they had started testing the intelligence of neurologically normal, but terminally ill volunteers, who agreed that their brains be measured after death. Insofar, Witelson has gathered data on 100 persons.
"My admiration for these people is profound," says Witelson. "It is a difficult and sensitive issue for patients and family members, to decide to leave a part of yourself for medical research. These were people with limited life spans who were willing to give up time for research. Their reasons for agreeing to do this differed but were important to them - they wanted to make some kind of contribution to the medical community or to leave something behind that would be useful for future generations. They often said, 'Perhaps the research will help my grandchildren.'"

Witelson has found that the linguistic intelligence of women in general and of right-handed men is strongly correlated with brain size.
However, in case of left-handed men, who have a bilateralization of language function - i.e. their ability to speak, read and write is mediated by both sides of their brain - linguistic intelligence is less correlated with brain size.
For determining why are there such differences between men and women, she conducted studies of the temporal lobe of the cerebral cortex, the specific area of the brain that perceives language, and discovered that women have about 11 per cent more brain cells in cortical layers of the area than men. This is why although the brain size of men is 10 percent larger than that of women, there are no significant differences in intelligence between men and women. This may also account for some of the well-known cognitive and emotional differences between men and women.

In case of spatial intelligence the team has found that it is correlated with brain size in women, but less strongly than the linguistic intelligence. However, in case of men spatial intelligence is not at all related to brain size. This suggests that women use their linguistic intelligence in spatial thinking, while in men these two types of intelligence are more distinct.

Finally, maybe the most interesting find is that men's brain size diminishes as they get older, indicating a decrease of the linguistic intelligence with age, while in case of women age hardly affects the brain size at all. It is not known what protective factors, which could be genetic, hormonal or environmental, operate in women.
"It remains to be determined what the contribution of nature and nurture are to this cerebral size relationship with intelligence," Witelson said.