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.

The study by UB researchers strongly implies the existence of other sex-differentiated cognitive functions. It predicts 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 study, published in the August issue of NeuroReport, was headed by Jeri Jaeger, associate professor of linguistics, and Alan Lockwood, 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.

The principal findings are :

- 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.

- In women, the brain is organized bilaterally for both simple and complex language functions. That is, regardless of the complexity of the task, females solve 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.

- 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 neuro-imaging 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 women continued to demonstrate bilateral activation. This finding runs counter to prevailing assumptions in the field that language is left-lateralized for everyone.

The long-held assumption that language function is located in the left cortical hemisphere is based largely on brain studies of men, Jaeger said. Upon it rests a vast body of research that models and predicts brain development, behavior and therapeutic processes.

"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."

The study co-authors are Robert Van Valin, Brian W. Murphy, and David S. Wack, all of UB, and David Kammerer, of the University of Iowa