Hormones can go to your head
A summary by Sara Abdulla describes a study by S. Marc Breedlove of the University of California, Berkeley, and colleagues , of an area of the medial part amygdala - the posterodorsal nucleus (or 'MePD' for short), published in the Proceedings of the National Academy of Sciences.
They have found that male/female volume differences in one brain area can be completely accounted for by differences in circulating androgens, such as testosterone. As the researchers explain, this region (also involved in the sense of smell) is usually about 65% larger in male rats than in females. When Breedlove's team castrated adult male rats to reduce their androgen levels, the rats' MePDs shrunk to female size within four weeks. Castrated rats that were given androgen replacement, on the other hand, held on to their large MePDs.
Similarly, when the group treated female rats with extra androgens over several weeks, their MePDs enlarged to the size customarily found in males. In many ways the plasticity of this particular area is not such a surprise. The medial amygdala is rich in androgen and estrogen receptors, and are involved in processing smell, motivation and emotion.
At the time of Zhou's study, the prevailing dogma was that brain structures are present at birth and remain unchanged through life. It would seem that this is too simple a view.
Bland, J., (1999) About Gender: Hormones can go to your head
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Last amended 10.07.99