The finding led to an unexpected discovery: Many brain areas communicating with the amygdala in men are engaged with and responding to the external environment. For example, the visual cortex is responsible for vision, while the striatum coordinates motor actions. Conversely, many regions connected to the left-hemisphere amygdala in women control aspects of the environment within the body. Both the insular cortex and the hypothalamus, for example, receive strong input from the sensors inside the body.
"Throughout evolution, women have had to deal with a number of internal stressors, such as childbirth, that men haven't had to experience," Cahill said. "What is fascinating about this is the brain seems to have evolved to be in tune with those different stressors."
Cahill believes this study could be the basis for a fuller understanding and treatment of a number of disorders that affect one gender or the other. For example, in the study, one of the brain areas communicating with the amygdala in women is implicated in disorders such as depression and irritable bowel syndrome, which predominantly affect women.
Cahill has led the way in exploring gender-related differences in the brain. In a 2001 study, he showed that the sexes use different sides of their brains to process and store long-term memories. In another study in 2002, he demonstrated how a particular drug, propranolol, can block memory differently in men and women.