Between 5,000 and 10,000 functional MRI studies are completed annually in the United States. The study, published in the March issue of the American Journal of Psychiatry , measured primary visual cortex responses to flashing light in 16 healthy subjects, eight men and eight women, aged 20 to 36. The findings show that responses in women were 38-percent lower than those in men.
Most studies show women have more brain functioning.
The findings also point to differences in the location of the brain's responses, indicating additional neurobiological significance. In men, brain activity was asymmetrical and more in the right hemisphere, and in women, responses were equal in each hemisphere. Functional MRI, a technology that provides rapid-fire brain images by measuring changes in brain blood oxygenation levels, has created enormous advances in scientists' ability to look at the living human brain. Previous functional MRI studies have not taken into account that blood itself is different in men and women. This difference alone will influence literally hundreds of other studies.