Study findings a no-brainer

A study has shown that brain shrinkage occurs only in ageing men, although cognitive performance remains constant.

Like the human body, the human brain is sexually dimorphic: the female brain is around 10 per cent smaller on average than the male brain, but compensates by packing in around 10 per cent more neurons.

Now, a 20-year study by Australian National University researchers has revealed that the disparity between the sexes reduces progressively with age, as the male brain shrinks.

Study leader Prof Helen Christensen, director of the ANU's Centre for Mental Health Research said that brain shrinkage occurs only in ageing men. The good news is that it seems to have no obvious effect on their performance in learning and memory tests.

It has long been known that the brains of Alzheimer's patients shrink dramatically as the disease progresses, resulting in severe cognitive impairment, especially in memory-related tasks.

Christensen said the focus on diseased brains has distracted research attention from what happens to healthy brains with age.

The Centre for Mental Health Research has been following a cohort of aging Canberrans for the past 20 years. The participants are now aged between 60 and 64.

Using magnetic-resonance imaging (MRI) of the volunteers' brains, the researchers measured the total volume of white and grey matter, as a percentage of the volume of the intracranial cavity.

Christensen said her group now plans to track volumetric changes in the hippocampus, which mediates memory, to see if shrinkage correlates with memory deficits in age.

She said the significant shrinkage of the male brain with age may simply be a reflection of women's superior health status. "There's a strong association between health and gender. Women live longer than men, and are likely to have fewer medical symptoms as they age," she said. The shrinkage is not a late-onset phenomenon. "The brain does shrink from early adulthood onwards," she said.

"Memory and cognition also change from early adulthood, but these are normal developmental processes. There is certainly evidence when we look at things like a person's capacity for language, something we call 'crystallised intelligence' increases with age."