There ’ s still a lot to figure out , though . Neuroscientists have observed subtle differences in the brains of people who stutter , but they can ’ t be certain if those differences are the cause or a result of the stutter . Geneticists are identifying variations in certain genes that predispose a person to stutter , but the genes themselves are puzzling : Only recently have their links to brain anatomy become apparent .
Maguire , meanwhile , is pursuing treatments based on dopamine , a chemical messenger in the brain that helps to regulate emotions and movement ( precise muscle movements , of course , are needed for intelligible speech ). Scientists are just beginning to braid these disparate threads together , even as they forge ahead with early testing for treatments based on their discoveries .
Slowed circuitry
Looking at a standard brain scan of someone who stutters , a radiologist won ’ t notice anything amiss . It ’ s only when experts look closely , with specialized technology that shows the brain ’ s in-depth structure and activity during speech , that subtle differences between groups who do and don ’ t stutter become apparent .
The problem isn ’ t confined to one part of the brain . Rather , it ’ s all about connections between different parts , says speechlanguage pathologist and neuroscientist Soo-Eun Chang of the University of Michigan in Ann Arbor . For example , in the brain ’ s left hemisphere , people who stutter often appear to have slightly weaker connections between the areas responsible for hearing and
for the movements that generate speech . Chang has also observed structural differences in the corpus callosum , the big bundle of nerve fibers that links the left and right hemispheres of the brain .
These findings hint that stuttering might result from slight delays in communication between parts of the brain . Speech , Chang suggests , would be particularly susceptible to such delays because it must be coordinated at lightning speed .
Chang has been trying to understand why about 80 percent of kids who stutter grow up to have normal speech patterns , while the other 20 percent continue to stutter into adulthood . Stuttering typically begins when children first start stringing words together into simple sentences , around age 2 . Chang studies children for up to four years , starting as early
On left , a brain scan shows the location of a brain region that is implicated in stuttering : the arcuate fasciculus in the frontoparietal lobe ( arc-fp ). A second region involved in stuttering , the arcuate fasciculus in the temporal lobe ( arc-t ), is also shown . The graph on the right shows changes in a measure of nerve-fiber connectedness called fractional anisotropy ( FA ) in the arc-fp as children age . Connectedness of the arc-fp increases for non-stuttering children ( gray line ) and recovered stutterers ( green line ) but does not improve for persistent stutterers ( blue dashed line ).
CREDIT : H . M CHOW & S . E . CHANG / HUMAN BRAIN MAPPING 2017
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