At the University of Wisconsin-Madison, a team led by Douglas Dean studied one-month old infants (77 infant girls and 72 infant boys) who were brought in there by their mothers for brain scanning one month after giving birth.
The results revealed that the boys’ brains were 8.3 per cent bigger, in line with the sex difference in brain volume found in adults and the few other available infant studies. Also as seen in adults, male brains had relatively more white matter (connecting tissue) and female brains more grey matter, relative to total brain size.
A number of specific neural areas were larger in males, also relative to total brain volume, such as parts of the limbic system involved in emotions, including the amygdala, insula, thalamus and putamen. On the other hand, female brains were relatively larger in other limbic areas such as parts of the cingulate gyrus, caudate and parahippocampal gyrus, and had a few white-matter structures that were relatively larger.
On average, men and women differ psychologically in small but reliable ways, such as in personality, interests, and cognitive performance, but the basis of these differences is up for debate as per the recent findings. Are they innate or due to how we are socialized?