Turhan Canli, a Stanford psychologist, recently tested 12 men and 12 women in functional MRIs and showed that women encode memories using different pathways than what men use when recording memories. The women were later able to recall emotions of a memory more accurately than men, which could possibly stem from how their memories were encoded in the first place.
Other differences keep emerging, including variability in size of the different brain regions, including the hippocampus, the amygdala and certain brain cell clusters.
"At least 100 sex differences in male and female brains have been described so far," said Forger. "They keep cropping up in animal and human studies."
So what lies at the root of the male-female variability? In mammals, testosterone appears to be a main player.
Forger's work in mice has shown that as mammals develop in the womb, testosterone and related hormones trigger cell death in some regions of the male brain and foster cell development in other regions. In this way, the hormone sculpts the male brain and how it will differ from the female version.
Remove or add testosterone to mice shortly after birth, and their brains develop according to the presence of the hormone, regardless of their sex.
Just as the Harvard president's remarks created a stir, this kind of research remains controversial, as does any work that looks for explanations for human behavior in the brain.
But most researchers looking into differences of the brain are quick to point out that there are many more differences in the brain just between individuals than between groups of people or between the sexes.
"Men and women are more the same than different in the brain -- without a question," said Forger. "But," she added, "little differences can go a long way."