Searching for a Cause

Given how complicated speech production is, it's a small wonder that more people don't stutter. Speech engages a wide swath of the upper body, starting with inflation of the lungs and expansion of the chest cavity and diaphragm. Vocal chords vibrate in the larynx; muscles in !the lips, jaw and tongue help articulate the sounds; and the ears provide quality control.

Command central for speech--as well as most everything else--is the brain. "From a neurological perspective, language takes up more parts of the brain than any other task, and it doesn't take much of an error to throw it out of whack," observes Lawrence Molt, Ph.D., a speech pathologist and neuroscientist at the Auburn University Neuroprocess Research Laboratory. "If you hold the motion of a muscle 20 milliseconds, often the system will break down. It will all tumble like a deck of cards."

Do the brains of stutterers behave differently from those of normal speakers? Scientists have been trying to figure that out since the 1930s. In fact, some of the earliest EEG research involved people who stutter. "Unfortunately, the technology of the time for neurological function couldn't tap into subtle differences," says Molt.

The next 50 years did bring some discoveries, including the finding that stutterers did worse than others in distinguishing competing sounds that were presented to them at the same time. But only since the late 1980s have scientists been able to figure out what's really going on inside the stutterers' heads, by mapping blood-flow patterns.

Positron Emission Tomography (PET), which creates color scans of the functioning brain, have provided the clearest picture yet of what happens when people speak. Gerald Maguire, M.D., an assistant professor of psychiatry at the University of California, Irvine, has shown that when stutterers stammer out their words, they have low levels of activity in two parts of the brain key to speech: Broca's area and the striatum. These sites also show elevated levels of dopamine, a neurochemical that regulates the striatum.

Scientists had suspected a link between dopamine and stuttering even before PET scans were available. As part of experiments in the 1970s, people who stutter were given dopamine-receptor blockers like haloperidol (Haldol), which depress the neurochemical's activity in the brain. Though speech improved somewhat, the drugs had intolerable side effects: participants felt like they were mired in quicksand. "Even people who experienced benefit said, 'Ah, I'd rather stutter than walk around like a zombie,'" remembers Molt, who stutters himself and was involved in the early trials.

In the last five years, scientists have been developing new medications, particularly risperidone and olanzapine, that block dopamine's activity by at least 50%, but with fewer of the numbing and debilitating side effects. Clinical trials are now under way with these drugs.

So far, according to Maguire, the results are promising. The medications seem to reduce the frequency of stuttering by about half. "It doesn't cure the problem," says Maguire, "but it helps treat it." The drugs are not perfect, however; users complain of lowered sex drive, missed menstrual periods, weight gain and fatigue. Maguire says the initial results warrant further testing, but people shouldn't get too excited, since stuttering appears to be a disorder without a single cause.

Because so many stutterers also have relatives who stutter, one area drawing attention is whether stuttering has a genetic component. Studies of families with multiple stutterers--especially those with stammering twins--strongly suggest a genetic link. Scientists believe that many genes play some part in stuttering, but hope to identify one that is more critical than others.

Still, notes Ehud Yairi, Ph.D., a professor of speech and hearing science at the University of Illinois at Urbana-Champaign in a recent issue of Asha, the official publication of the American Speech-Language-Hearing Association, "the knowledge of how stuttering is being transmitted does not tell us what is being transmitted. We still do not know if stuttering evolves from an inheritance of abnormalities in one or more biochemical pathways involved in speech fluency, or even from structural difference." Faulty brain processing or motor skills as well as altered emotional states or any combination could have an impact.

One of the mysteries of stuttering is why it appears more commonly in men than women. Researchers offer many possible explanations, covering everything from sex-linked genetic factors to the effects of testosterone on the brain. One theory holds that stuttering might be linked to other apparently brain-related syndromes that appear with greater frequency in males, including attention deficit hyperactivity disorder (ADHD), learning disabilities and language development problems. Another popular theory holds that men's brains deal with language differently than do women's when it comes to neural organization and function. "That may make men a bit more susceptible," says Molt.

More research and more sophisticated technology, say scientists, will yield the ultimate answer to why people stutter.

PHOTO (COLOR): As subject listens and repeats words, blood flows to brain's speech area (yellow dot, above) as well as listening center (below)

PHOTO (COLOR): PET scan shows blood flow (yellow and red) to brain's auditory center as a normal subject hears words spoke