New Study Overturns Century-Old Assumptions About Cognitive Functions of Men And Women

BUFFALO, N.Y. -- The first study to use Positron Emission Tomography (PET) to compare the cognitive functions of men and women has found definitive evidence that although in many respects male and female brains operate in much the same way, they function differently when performing complex linguistic tasks.

This contradicts the assumption widely held by neuroscientists for more than a century that the brains of women and men are organized functionally the same way for language. It strongly implies the existence of additional sex-differentiated cognitive functions as well.

The UB findings, they added, predict a major, new direction in pure and applied research in neurology, developmental psychology, pediatrics, linguistics, aphasiology (the study of the language disorders caused by brain trauma) and other neurosciences.

The Buffalo study, published in the August issue of NeuroReport, was headed by Jeri Jaeger, Ph.D., associate professor of linguistics, and Alan Lockwood, M.D., professor of neurology and nuclear medicine, and adjunct professor of communicative disorders and sciences.

Both are members of the university's Center for Cognitive Science, and Lockwood is director of PET operations in the Center for Positron Emission Tomography, a joint project of UB and the Veterans Administration of Western New York Healthcare System.

o In men, the brain is organized bilaterally only for simple language functions, such as simple reading tasks. When the task is complex, that is, associated more with grammatical or lexical tasks that require in-depth linguistic processing, males show more robust left lateralization of the cerebral cortex.

o In women, the brain is organized bilaterally for both simple and complex language functions. That is, regardless of the complexity of the task, females solved it by engaging the left and right hemispheres of the cerebral cortex. The higher activation in females' occipital and/or cerebellar regions suggests sex differences in basic reading strategies.

o Despite sex-differentiated variances in neural-activity patterns, there were no meaningful differences in outcomes between male and female subjects as measured by speed of performance and error rates.

The brain lateralization patterns uncovered in the UB study may correlate with sex-based differences in information processing, superior female performance on language tasks and superior performance by men on visual-spatial tasks, according to Jaeger.

She said they also suggest the need to develop gender-based rehabilitation strategies to treat aphasia and other disorders related to traumatic brain injury.

Until now, the fundamental and controversial question of whether the brains of men and women are organized functionally the same way for language has remained unanswered, despite more than a century of research in cognitive science.

Contradictory outcomes reported by previous studies are due to the fact that even when test subjects included both men and women, researchers usually did not analyze their results by sex, Jaeger said.

In reviewing the few neuroimaging studies that have focused on sex differences in cognitive function, she noticed that, despite conflicting results, the studies suggested that functional differences based on sex were more likely when the linguistic demands of the task are greater.

Although the UB study set out to examine that premise, Jaeger said researchers were amazed at the clear and consistent patterns of differentiation that emerged.

PET scans were used to track blood flow in the cerebral cortex of nine male and eight female subjects as they performed two simple and three complex language tasks. Blood flow in the cortex indicates the ebb and flow of brain activity. This methodology locates the specific areas of the cortex activated during the performance of discrete tasks.

The researchers found that during simple language tasks, all subjects demonstrated bilateral activity in the cerebral cortex. (i.e., activity in both the left and right cortical hemispheres). This indicates that when solving simple tasks requiring awareness and judgment, the brains of men and women operate in a similar way.

During complex tasks, however, men exhibited strong left-lateralization, while woman continued to demonstrate bilateral activation. This finding runs counter to prevailing assumptions in the field that language is left-lateralized for everyone.

This assumption is based on the fact that research subjects for brain studies are usually men and that the studies themselves have seldom differentiated the outcomes according to the sex of the subjects.

"Unfortunately," she said, "we've had the mistaken impression that what we've learned from male subjects can be applied to women as well.

"In fact," she said, "virtually all of our ideas about the brain from the fields of neurology, psychology and linguistics are modeled after studies of male brains, as are all the ideas on cognitive function in our textbooks. They will have to be re-evaluated, new cognitive models designed and new therapeutic approaches to women developed and tested."

In a paper presented in April to the Berkeley Women and Language Group, Jaeger discussed the implications of the UB findings for the field of aphasiology.

Aphasia is the loss or impairment of the power to use or comprehend language. It is usually produced by a brain lesion, as occurs in a stroke or other trauma. In the case of aphasia caused by a left-brain lesion, medical clinicians usually will try to stimulate activity in the left cerebral cortex. This is because studies of male subjects indicate that this is the place where complex language tasks are solved.

"Since our research shows that in women, language is stored and activated in the right side of the brain as well as the left," Jaeger said, "therapeutic stimulation of the right cerebral cortex may be effective in improving or restoring function in aphasic women."

The study co-authors with Jaeger and Lockwood are Robert Van Valin, Ph.D., professor and chair of the UB Department of Linguistics; physicist Brian W. Murphy and computer specialist David S. Wack, both research assistant professors in the Department of Nuclear Medicine, UB School of Medicine and Biomedical Sciences, and David Kemmerer of the University of Iowa.