WEST LAFAYETTE, Ind. – New research from Purdue University shows that even when people who stutter are not speaking, their brains process language differently.
"Traditionally, stuttering is thought of as a problem with how someone speaks, and little attention has been given to the complex interactions between neurological systems that underlie speaking," says Christine Weber-Fox, an assistant professor of speech sciences who is interested in the brain's involvement in language processing.
"We have found differences in adults who stutter, compared to those who don't, in how the brain processes information when people are thinking about language but not speaking. For example, there was a significant delay in response time when subjects were given a complex language task. We also found that in people who stutter, certain areas of the brain are more active when processing some language tasks."
Weber-Fox, a cognitive neuroscientist, teamed with Anne Smith, a professor of speech science who studies the neurophysiological bases of speech production, to study language and speech production systems. A series of studies were conducted to measure semantic (word meaning in sentence processing), grammatical and phonological (sounds of the language, such as rhyming) aspects of language. In each study, the brain activity of adults who stutter and don't stutter were measured when they responded silently, by pressing a button, to questions regarding sentence meaning, grammar or sentence structure, and rhyming. This is believed to be the first time brain electrical activity has been studied in a series of language tasks in people who stutter to determine whether their brains function differently even when there are no overt speaking demands.
The researchers' findings will be presented Friday (July 23) in Portland, Ore., at the American Speech-Language Hearing Association's conference on Fluency and Fluency Disorders. Their study, "Phonologic Processing in Adults Who Stutter: Electrophysiologic and Behavioral Evidence," will be published in August in the Journal of Speech, Language and Hearing Research. The research was funded by the National Institutes of Health.
"Adults who stutter often have great language skills, meaning they don't have problems with rules of grammar or with the sounds we use to code the words of our language," Weber-Fox says. "When they speak, however, their motor output falters, so they pause or trip over words. We wanted to evaluate the brain activity when they were not stuttering and, in fact, when they were not having to engage their speech motor systems."
Smith, who also is head of Purdue's Department of Audiology and Speech Sciences and has been studying the physiological aspects of stuttering since 1988, says, "Neither a cause nor treatment has been found for stuttering," "Our research found many complex interactions between the language and motor systems, which leads us to believe that there is no single cause for stuttering. Stuttering is the result of a complex interaction among many factors, including genetic, language, motor and emotional. But our research found many complex interactions between the language and motor systems, which leads us to believe that there is no single cause for stuttering. These findings will help reduce the stigma – such as the myth that the disorder is the result of poor parenting or a psychological problem – often associated with stuttering."
Stuttering, which interrupts the flow of speech, affects 5 percent of people in the United States at some time in their lives. Stuttering usually begins in the preschool years, and there is a higher incidence in males. Characteristics of the disorder can range from repetition of sounds, prolongation of syllables, elongated pauses between words and speech that occurs in spurts.
Weber-Fox and Smith's most recent study focused on phonological aspects of language, specifically rhyming. Just as in the earlier studies that evaluated responses to semantic and grammar language tasks, brain activity was measured in milliseconds. This non-invasive technique uses a skull cap with electrodes to measure activity for groups of brain cells. Response accuracy and time also were measured in this study.
In the rhyming study 22 subjects, half of whom stutter, saw a series of two words flash on a computer screen. Their task was to identify which pairs of words rhymed without saying the word out loud. Some word groups were spelled alike but did not rhyme, such as "gown" and "own," and others did not look similar but did rhyme, such as "cone" and "own." The other variations were words that looked similar and did not rhyme, such as "gown" and "own," and words that did not look similar or rhyme, such as "cake" and "own." This method evaluated the adults' ability to translate sounds when not verbalizing them.
The researchers found that individuals who stutter experienced similar brain activity, response accuracy and response time when it came to three of the four rhyming variations. For example, if two of the words look alike and rhyme, such as "thrown" and "own," most people can quickly identify that they rhyme. But if two words look alike but didn't rhyme, such as "gown" and "own," then the response was delayed to 410 milliseconds for those who stutter. The other three variations averaged about 350 milliseconds among all participants.
"We saw no difference in the fundamental processing when looking at words like gown and own," Weber-Fox says. "The difference was in the complexity of the language task. Also of note during this study was the increase in activity in the brain's right hemisphere for participants who stuttered as they viewed the rhyming words. This shows the individuals who stutter are using right hemisphere brain areas to a greater extent to accomplish the rhyming tasks than those who don't stutter."
Weber-Fox says this relationship to the right hemisphere is a consistent finding that has been shown in other forms of brain imaging, such as functional magnetic resonance imaging. The right hemisphere is considered the non-dominant hemisphere for language, and the activity may indicate that the right hemisphere is compensating for something that is not happening in the left hemisphere, she says.
In similar experiments, the researchers are now looking at stuttering in children and are introducing a hearing task for adults who stutter.
"We looked at the brain's reaction when reading words, and now we are focusing on hearing words," Weber-Fox says. "Do we see atypical responses when somebody who stutters is listening to sentences instead of reading them? We have preliminary data that suggests yes."
Purdue's Department of Audiology and Speech Sciences is ranked among the top 10 in the nation by U.S.News & World Report. The master's and doctoral degree program in speech-language pathology and audiology are ranked third and eighth, respectively.
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