Men and women use different sides of their brains to store memories of emotional experiences 

UC Irvine Study points to gender as vital in understanding memory function 

Irvine, Calif., January 8, 2001 — The far-fetched idea that emotionally men are from Mars and women from Venus may have a biological basis after all. The two sexes use different sides of their brains to process and store long-term memories of emotional experiences, a UC Irvine study shows.

In testing how men and women store these type of memories, a UCI research team found that the amygdala, an almond-shaped structure found on both sides of the brain, processes emotionally influenced memories exclusively on the right side of the brain in men and on the left side in women. Their results appear in the January 2001 issue of the journal Neurobiology of Learning and Memory.

"While we don't yet know why this occurs, these results demonstrate a clear gender-related difference in amygdala involvement in the formation of emotionally impacted memories," said Larry Cahill of UCI's Center for the Neurobiology of Learning and Memory, who led the study. "They also suggest that further research on memory must take gender into consideration."

The amygdala's primary function is to process memories for emotions. When a person views an emotionally charged event, such as violence, the amygdala is triggered into action by hormones released by the body to enhance long-term memories as they are formed and stored. "Because of the boost the amygdala provides, people have more explicit and detailed memories of emotionally powerful moments," Cahill said. "This activity separates how we remember these events from the mundane activities of our everyday lives."

In the study, 22 participants-11 women and 11 men-viewed two films, one composed of emotionally neutral images and the other of emotionally charged images meant to elicit negative feelings such as fear and disgust.

While the participants viewed the films, the researchers traced brain activity using a positron emission tomography (PET) scanner, which allowed them to follow radioactively labeled sugar as it traveled to different parts of the brain, where it was taken up by cells as food. More active parts of the brain metabolized more of the radioactive sugar, which appeared on the PET scan.

PET scans of the 11 women revealed significant activity related to memory for the emotional film in the left amygdala but none in the right one. Scans of the 11 men showed completely opposite results-activity in the right amygdala but none in the left. PET scans after the emotionally neutral film showed no significant amygdala activity.

The researchers also found that while amygdala activity differed between the men and women participants, their assessments of the film content were relatively uniform. In rating how emotional they found the content, the reactions among the men and women did not differ significantly. When given a surprise memory test for the films three weeks later, all participants recalled a similar amount of detail.

"What's interesting about these tests is that the activity is exclusively in the right or left amygdala and not on the other side," said Cahill, an assistant professor of neurobiology and behavior. "This means that the brains of the men and women simply could not have been storing memories of the films in the same way. But we don't know too much more than that right now. That's why we must begin to better understand the advantages that sex and hemisphere differences confer as the brain stores memories of emotional events. These neurobiological results are even forcing us to go back to the psychological level to find differences in what men and women remember about emotional events that previous studies have apparently missed."

The UCI study is one of several projects conducted by neural researchers nationwide over the past several years that have discovered differences in how men's and women's brains function. Sex-related differences also have been found in research on listening, language, navigational ability, defensiveness, attention, metabolism and mathematical ability. "We're witnessing the leading edge of a wave that will shake neuroscience a great deal in coming years," Cahill said.

In addition to Cahill, the UCI research team included Lisa Kilpatrick and Chris Lawrence of the Department of Neurobiology and Behavior, Nathan S. White and Michael T. Alkire of the Department of Anesthesiology, Richard J. Haier of the Department of Pediatrics, James Fallon of the Department of Anatomy and Neurobiology and Steven G. Potkin of the Department of Psychiatry and Human Behavior. The study was supported by the National Institute of Mental Health.

Tom Vasich
(949) 824-6455
tmvasich@uci.edu

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