Sex differences found in human brains.

The most conspicuous difference between male and female brains is that reported in rodents for an area playing a role in sexual hormone release and sexual behavior. This structure in males is larger and contains more cells than in females. Now Dutch scientists report a similar sex difference in human brains. Although there have been previous reports of shape differences for two other areas of the human brain, the scientists believe theirs is the first evidence of sex differences in cell number for any human brain area.

Brains of 13 men and 18 women were obtained at autopsy and examined by D.F. Swaab and E. Fliers of the Nethelands Institute for Brain Research in Amsterdam. One area, called the sexually dimorphic nucleus of the preoptic area (SDN-POA), was found to be on the average 2.5 times larger in men than in women and to contain 2.2 times as many cells, they report in the May 31 SCIENCE. In both sexes, the volume of this area and the number of cells within it decreased with age.

The sex and age differenges observed are specific to the SDN-POA. In the same brains, a nearby area, the suprachiasmatic nucleus, which shows a sexual difference in shape, did not display a sex or age difference in volume or in cell number. The exact role of the SDN-POA and the chemical nature of the sex differences remain unknown.