Rudolf Uher and his colleagues at King’s College London Institute of Psychiatry used functional magnetic resonance imaging (fMRI) to test reactions to food in the brains of 18 men and women after they had either eaten normally or fasted for 24 hours. When the volunteers were shown photographs of food or given food to taste, a part of the brain that processes visual information about food reacted more strongly in the women than in the men, whether they were hungry or not – a difference that did not occur when non-food pictures were shown.

The strongest activity was in the occipitotemporal cortex, a region that monitors and reflects how other areas of the brain – such as those processing hunger and feelings of pleasure – react to food. This suggests that the women were engaging in more conscious thought and decision-making in response to the stimulus.

Uher says this could be related to biological differences between men and women, but he believes the more likely explanation is that women have a more complicated reaction to food because of social pressure. “My personal bet would be to set more store by learning processes,” he says.

Confirming Uher’s speculations will need specific testing, cautions Angelo del Parigi of the John B. Pierce Laboratory in New Haven, Connecticut. His research echoes Uher’s finding, but looking at fMRI alone cannot confirm whether this is due to innate differences or a learned process, he says.

Uher’s team is now applying its findings to patients with eating disorders, 9 out of 10 of whom are women. Compared to healthy women, those with anorexia or bulimia show greater activity in the occipitotemporal cortex when shown pictures of food, possibly reflecting their negative perception and heightened awareness of food. “We found a reaction even in motivational areas that are very difficult to pick up with fMRI,” Uher says. He also plans to explore how obese people react to similar pictures.

The brain’s cortex thickens in childhood, reaches a peak, and then thins again in adolescence. To see how this pattern is related to intelligence, Philip Shaw and colleagues at the National Institute of Mental Health in Bethesda, Maryland, US, scanned the brains of 307 children every two years on average from age 6 to 20. On the basis of IQ tests, the children were categorised as having average, high or superior intelligence.

In the brightest children, the thickness of the prefrontal cortex – a brain region thought to be responsible for many facets of intelligence – increased rapidly through their pre-teen years before thinning out again after the age of 11. The pattern was the same in those of average intelligence, but much less pronounced.

Nature plus nurture

In all three groups, the children’s IQs correlated with their parents’ job and education. “The ultimate determinants of intelligence will likely prove to be a very complex mix of nature and nurture,” notes Shaw.

The researchers are still in the dark about how the thickness of the cortex affects intelligence at a finer-grained level. “We know very little of what is happening at a cellular level,” Shaw says. He speculates that a “use it or lose it” pruning mechanism might act on cortical nerve connections.

He believes it may be the way the brain is used that counts, rather than size. “Brainy children are not cleverer solely by virtue of having more or less grey matter at any one age”, says Shaw. “In a way, children with the most agile minds have the most agile cortex.”

Journal reference: Nature (vol 440, p 676)