July 9, 2001 WASHINGTON — To recognize faces and identify facial expression, both with equal skill, pre-pubescent boys use more of their right brain and pre-pubescent girls use more of their left brain. This suggests that the brains of males and females are organized differently before adulthood, and may mean that men and women who suffer brain injuries will benefit from different treatment regimes. These findings are reported in the July issue of Neuropsychology, published by the American Psychological Association (APA).
At the State University of New York at Buffalo School of Medicine and Biomedical Sciences, D. Erik Everhart, Ph.D., Janet L. Shucard, Ph.D., Teresa Quatrin, M.D. and David W. Shucard, Ph.D. studied 17 boys and 18 girls between the ages of 8 and 11 years. Given previous evidence for the brain’s right-hemisphere superiority in face processing, as well as adult male superiority at spatial and non-verbal skills, the research team studied pre-pubescent children to see whether boys’ and girls’ brains are already differentiated in these areas before puberty.
In the study, the children performed two different types of tasks. For the face-recognition-memory task, they viewed a series of three-slide sets. In each set, the first slide had a face with an “X” in the middle to fixate their gaze; it served as a baseline. The second slide gave them a “target” face to study. The third “recognition” slide offered three faces, from which they had to choose the target face regardless of expression. Researchers used an electroencephalo-graphic (EEG) measure, called the Event-Related Brain Potential, to study how the children’s brain waves changed in the left and right hemispheres as they performed this task.
In the second task, facial affect (emotional expression) identification, the children viewed 24 pairs of slides. For the first slide of each pair, they had to pick which face of four along the bottom displayed an emotion matching that of a single face at the slide’s top. In the second slide, four faces were the same as the top face of slide one, but with different feelings. The children had to pick the face whose feelings matched the feeling shown in the first slide. There was no EEG measurement; instead researchers tallied the children’s accuracy and response times.
Supporting the researchers’ hypothesis, prepubertal boys showed significantly greater right- versus left-hemisphere activity during the presentation of face stimuli, whereas girls displayed significantly greater left- versus right-hemisphere involvement. What’s more, boys’ right-hemisphere activity correlated significantly with their accuracy in identifying facial affect -- a relationship not demonstrated for girls. Boys and girls performed equally well on all tasks, but, the authors say, “they may use differing, though overlapping, neuronal systems to complete the task.”
“It is possible,” the authors speculate, “that boys process faces at a global level (right hemisphere), whereas girls process faces at a more local level (left hemisphere).” If so, they add, “the girls’ approach could be more of an advantage in detecting the fine changes in affective expression, and thus they would be better at reading people.” The findings, says Erik Everhart, do not reflect an “either-or” phenomenon, but rather a tendency to use different neuronal systems successfully, with many individual differences.
Finally, the authors explore the study’s important implications for how injury to different parts of the brain, for example from strokes, might differently affect the sexes. “The deficits in face processing and emotion perception that occur following injury to this [face-processing] region,” they write, ”impact the patient socially and have wide-ranging effects on their relationships, employment and more.” Understanding the differential damage caused by a brain lesion can, they explain, help determine the course of treatment.
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