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Researchers created mice with a mutation in a gene that , in people , is linked to stuttering . The mutant mice vocalized haltingly , with longer pauses between syllables , similar to what ’ s seen in human stuttering .
Astrocytes do big jobs that are essential for nerve activity : providing the nerves with fuel , for example , and collecting wastes . Perhaps , Drayna muses , the limited astrocyte population slows down communication between the brain hemispheres by a tiny bit , only noticeable in speech .
Drayna ’ s research has received mixed reviews . “ It ’ s really been the pioneering work in the field ,” says Angela Morgan , a speech-language pathologist at the University of Melbourne and Murdoch Children ’ s Research Institute in Australia . On the other hand , Maguire has long doubted that mutations in such important genes , used in nearly all cells , could cause defects only in the corpus callosum , and only in speech . He also finds it difficult to compare mouse squeaks to human speech . “ That ’ s a bit of a stretch ,” he says .
Scientists are sure there are more stuttering genes to find . Drayna has retired , but Morgan and collaborators are initiating a large-scale study in the hopes of identifying additional genetic contributors in more than 10,000 people .
The dopamine connection Maguire has been tackling stuttering from a very different angle : investigating the role of dopamine , a key signaling molecule in the brain . Dopamine can ramp up or down the activity of neurons , depending on the brain location and the nerve receptors it sticks to . There are five different dopamine receptors ( named D1 , D2 , and so on ) that pick up the signal and respond .
During the 1990s , Maguire and colleagues were among the first to use a certain kind of brain scan , positron emission tomography , on people who stutter . They found too much dopamine activity in these people ’ s brains . That extra dopamine seems to stifle the activity of some of the brain regions that Chang and others have linked to stuttering .
Backing up the dopamine connection , other researchers reported in 2009 that people with a certain version of the D2 receptor gene , one that indirectly enhances dopamine activity , are more likely to stutter .
So Maguire wondered : Could blocking dopamine be the answer ? Conveniently , antipsychotic drugs do just that . Over the years , Maguire has conducted small , successful clinical studies with these medications including risperidone , olanzapine and lurasidone .