Hemispheric Cross Talk: Brains show two sides of language function

Damage to the brain’s left side often undermines language abilities. Occasionally, so does right-brain damage. Still, a lucky few individuals can suffer injury to either side and retain their verbal skills.

Thanks to a device that temporarily blocks activity in specific brain areas, scientists have uncovered a likely explanation for this linguistic reversal of fortune. Some individuals, conclude neurologist Stefan Knecht of the University of Münster in Germany and his colleagues, have strong language capabilities in both halves of their brains. These individuals have enough neural leverage to withstand a block on one side or the other, the researchers report.

In contrast, the majority of people, whose language capability relies primarily on left-brain structures, exhibit temporary verbal losses during brief disruptions of those areas. Comparable difficulties occur when the right brain is blocked in the smaller proportion of people who depend on that side to coordinate language use, the scientists report in an upcoming Nature Neuroscience.

“Some people possess a network of language areas on both sides of the brain that resists localized damage,” Knecht says.

Knecht’s group used functional magnetic resonance imaging to measure blood-flow changes in the brains of 324 men and women as they thought about as many words as possible beginning with letters shown on a computer screen. This method indirectly gauges cells’ activity throughout the brain.

The results suggest that about 1 in 10 people exhibits two-sided neural organization. Another 1 in 10 displays right-brain coordination of language. Both these brain patterns occur mainly in left-handers.

No difference in intelligence, creativity, or academic achievement shows up among the groups with left-brain, right-brain, or two-sided language control.

The researchers further studied 20 individuals. Each of these volunteers performed a second language task in which he or she noted as quickly as possible whether animal pictures were correctly labeled. These participants also wore caps with coils that briefly generated magnetic fields. This process, known as transcranial magnetic stimulation (SN: 9/23/00, p. 204: https://www.sciencenews.org/20000923/bob2.asp), enabled the scientists to suppress cell activity in either left- or right-brain tissue.

The six people identified as having two-sided language activity continued to do well on the picture-word task during both left- and right-brain suppression. However, performance plummeted for the seven participants with left-brain specialization for language and the seven with right-brain specialization when parts of their crucial neural hemisphere were suppressed.

Curiously, these individuals did slightly better at matching pictures and words during brief disturbances of their other hemisphere. Since the nondominant hemisphere analyzes the context of speech, its suppression might make it easier to perform simple word tasks, Knecht theorizes.

The new report confirms prior suspicions about left- and right-brain language functions, remarks psychologist Glyn W. Humphreys of the University of Birmingham in England. “The nature of language representation in the brain still remains unclear,” he adds.

Bruce Bower has written about the behavioral sciences for Science News since 1984. He writes about psychology, anthropology, archaeology and mental health issues.

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