A new imaging study finds that people who stutter show abnormal brain activity even when reading or listening. The results suggest that individuals who stutter have impaired speech due to irregular brain circuits that affect several language processing areas -- not just the ones for speech production.
The research was presented at Neuroscience 2010, the annual meeting of the Society for Neuroscience, held in San Diego.
Stuttering affects about one in every 20 children; most grow out of it, but one in five continues to struggle. While the particular cause of stuttering is still unknown, previous studies showed reduced activity in brain areas associated with listening, and increased activity in areas involved in speech and movement. In the new study, researchers considered whether irregular activity would also be apparent when stuttering speakers silently read.
"If those patterns are also abnormal, the differences could be considered typical of the stuttering brain and not just the result of the difficulties that people who stutter have with speech production," said senior author Kate Watkins, PhD, of the University of Oxford.
Using functional magnetic resonance imaging (fMRI), Watkins and her team compared the brain activity in 12 adults who stutter with 12 adults who do not. The researchers conducted the scans in three trials: in one, volunteers simply listened to sentences; in the second, they read sentences silently; in the third, they read sentences silently while another person read the same sentence aloud. The authors found the stuttering volunteers' brains were distinctly different from non-stuttering speakers in all three tests. The people who stuttered had more activity in auditory areas when listening only. When reading, there was less activity in motor areas, specifically a circuit involved in the sequence of movement.
"Our findings likely reflect that individuals who stutter have impaired speech processing due to abnormal interactions in brain circuits," Watkins said. "In future studies, it will be important to examine changes in these brain areas in young children to find out if these interactions result from a lifetime of stuttering or point toward the cause of stuttering itself."
Research was supported by the U.K. Medical Research Council.
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