New Study Ties Stuttering to Chemical Defect
The first concrete evidence that stuttering and a second speech disorder called spasmodic dysphonia are caused by biochemical abnormalities rather than by emotional disturbances was presented here Monday by University of Texas researchers.
Stuttering affects one in every 100 people in the U.S. and spasmodic dysphonia, in which the larynx spasms to choke off words, affects perhaps a tenth as many.
The discoveries, presented at a meeting of the American Assn. for the Advancement of Science, could remove much of the stigma and guilt associated with the disorders based on the belief that they are psychological in origin. The findings also provide new techniques for therapy that already are being used on an experimental basis.
Significance Cited
“Overall, I am very impressed with their study,” said audiologist Robert G. Turner of UC San Francisco, head of the Scientific Affairs Committee of the American Speech, Language and Hearing Assn. “It’s a very difficult problem to study, and their research strategy is very well designed. What’s really significant is that they have shown (the occurrence of a biochemical abnormality) using a variety of techniques.”
Everyone knows someone who stutters, hesitating at the beginning of some words and saying the first sound repeatedly until the entire word comes out. What has confused researchers is the fact that stutterers do not stutter all the time. Country singer Mel Tillis, for example, stutters when he speaks, but not when he sings.
Because of this variability, many psychiatrists believe that the disorder is caused by psychological trauma in childhood and have made parents feel unnecessarily guilty, according to speech scientist Frances J. Freeman of the Dallas Center for Vocal Motor Control of the University of Texas, one of the researchers on the project.
Spasmodic dysphonia typically develops in the 30s and 40s, but it can begin as early as the teen-age years or as late as the 60s. Most often, spasms close the larynx so that words are cut off, but in some patients the larynx muscles completely relax so that sounds cannot be made. The disorder is usually progressive, so that the victim eventually loses speech entirely.
Conventional Thought
Psychiatrists have assumed that the victims unconsciously wish to punish someone in their lives, and do it by ceasing to speak. The conventional therapy is thus psychoanalysis, but it has not proved effective.
The discoveries were made possible by the innovative combined use of several new techniques for imaging the brain and measuring metabolic activity and blood flow. The combination of these techniques provides “a unique window into the brain,” Freeman said.
Among the techniques used by the researchers were: magnetic resonance imaging or MRI, which uses magnetic fields to produce highly detailed cross-sectional images of the brain; brain electrical activity mapping or BEAM, in which electrical signals emitted by the brain are collected by electrodes and synthesized into a picture of electrical activity throughout the brain, and single photon emission computerized tomography or SPECT, in which radioactively labeled isotopes are injected into the blood stream to monitor blood flow through the brain and the brain’s consumption of sugar, which is a measure of how hard specific areas of the brain are working.
No single technique demonstrated that biochemical abnormalities were the cause of the disorder, according to neurologist Kenneth Pool, but the combined evidence was persuasive.
MRI, for example, showed that 24% of 51 patients with stuttering or spasmodic dysphonia had abnormalities in the structure of three specific regions of their brains, two of which are “classically associated with speech function,” Pool said. BEAM showed that as many as 64% of 43 patients had abnormal electrical activity in the same areas.
And SPECT showed that 76% of 49 patients had abnormally low metabolic activity in the same specific regions.
“We can say with great confidence that 84% of the people we have studied with these two disorders have a neurological defect of the central nervous system that causes the disorder,” said radiologist Terese Finitzo, the project director. The affected areas are not the same in the two disorders, but they are close enough together to suggest that both impairments might be subtly different manifestations of similar underlying damage, she said.
As for the other 16%, “Failure to find neurological dysfunction does not preclude its existence. It just means that our techniques aren’t sophisticated enough yet to see it.”
Once they realized the areas of the brain involved, the Texas researchers began to look for other bodily functions controlled by the same regions on the assumption that those functions would also be affected.
One region of the brain involved in spasmodic dysphonia, for example, also is involved in control of the digestive system. The Texas group found that victims of the speech disorder often have insufficient production of stomach acid and suffer from intestinal upsets.
Other areas are involved in motor control of the body, and researchers found that the spasmodic dysphonia victims (and many stutterers) have more trembling than normal in their hands and diminished coordination and reaction times. Such impairments were often overlooked by other physicians and the patients themselves because of concentration on vocal problems.
The discovery of these secondary effects is strong confirmation of the idea that the disorders are caused by a biochemical abnormality, according to radiologist Michael D. Devous, also a participant the 11-member research team.
However, the research still does not answer the question of why some stutterers are able to speak clearly part of the time.
The discoveries have suggested new avenues for treatment. The center now uses conventional speech therapy for spasmodic dysphonia extensively, a treatment approach that was ignored when the cause of the disease was thought to be psychological. The discovery of impaired blood flow to some regions of the brain is also prompting use of conventional drugs that dilate blood vessels and increase blood flow.
Therapists are also using drugs that are normally used to treat movement disorders caused by impairments in the same region of the brain. It is too early to tell if any of these approaches are working, Finitzo said, but the team has great confidence that one or more of the approaches will prove successful.
