UCI Scientists Link Stuttering to Brain Area

Dr. Gerald Maguire’s interest in stuttering dates back to the time he was a toddler, when he first tried to string sentences together.

Through the years, as listeners pleaded with him to “just relax,” he struggled to speak with the same fluency as those around him, always believing that it was a matter of psychic strength, of trying harder to force out the words trapped inside.

His research is proving him wrong.

The UC Irvine psychiatrist and his colleagues have traced the often-embarrassing, much-maligned disorder to a spot deep within the brain where a central switchboard activates speech circuits. According to their preliminary findings in four patients, the spot, known as the left caudate, is not nearly as active in stutterers as among those who speak fluently, which may disrupt the brain’s speech signals.

The research, published last month in the British journal Neuroreport, is not the first to suggest a neurological basis for stuttering, but it is the first to precisely pinpoint an anatomical culprit.

And while Maguire, 29, stresses that more people need to be studied, many stutterers are hailing the findings as the surest proof yet that their oral stumbling is not the outward sign of a tortured inner existence.

“It’s the best proof we have that stuttering is a medical problem, that people who stutter are not different in any way emotionally or psychologically,” said John Ahlbach, executive director of the National Stuttering Project, a San Francisco-based organization with 4,000 members.

“Some people will fight to their dying day, they’ll go from Gestalt to Rolfing to EST to anything that will provide the solution that they think is there . . . but from everything we know about the problem, it is wrapped up in how (the) body works, in how (the) brain handles speech,” Ahlbach said.

The researchers and some who have followed their work caution against all-or-nothing explanations, however.

Stuttering, which afflicts 2 million to 3 million Americans, may have a basis in biology, but “it doesn’t account for everything,” said Matt Ronayne, a speech pathologist who is president of the Stuttering Project’s Orange County chapter. “A lot of people who stutter . . . are struggling so hard to be fluent that they are actually creating what they are struggling against. . . . It’s kind of a paradoxical effect.”

Ronayne, a 33-year-old Huntington Beach resident, said many of the behaviors that accompany stuttering--shutting one’s eyes, for example, or clenching one’s fists in an effort to force out a word--are learned. The speech and the associated behaviors are worsened by anxiety and shame, he said.

Maguire and his fellow researchers, including UCI psychiatrist Joseph Wu and Cal State Fullerton speech pathologist Glyndon Riley, do not dismiss the role of psychology.

“If you’re more anxious and tense, you’re likely to stutter more,” Maguire said.

But their key finding, which they stress requires further testing, is that an underactive caudate is the primary reason for stuttering, with other factors--including anxiety--of secondary importance.

“We don’t want to say we have the answer,” said Wu, acting director of UCI’s Brain Imaging Center. But “we think this is a very important crack in the mystery of what causes stuttering.”

Riley, who has worked with stutterers for more than three decades, suspects that the caudate will not, however, turn out to be implicated in the case of every stutterer.

The team made its discoveries using a PET scan machine, an instrument that has explored the brain’s role in everything from schizophrenia to Parkinson’s disease.

The machine allows researchers to create color-coded images of brain activity. Subjects are injected with a sugar molecule attached to radioactive tracers, which then is taken up by the brain. Later, X-rays emitted by the tracers are detected by the machine and reproduced in a computer image, showing which areas of the brain have the most metabolic activity.

“This (technology) gives us an unprecedented telescope into the living brain,” Wu said.

In the Neuroreport research, the pictures of the four stuttering subjects’ brains were compared to those of four patients who do not stutter. In addition, pictures were obtained when the stuttering patients experienced speech problems and when they did not.

The images showed that among stutterers, brain activity is drastically reduced in the left caudate, an area the size of an almond at the brain’s core. This holds true whether the stutterer is in a period of fluency, suggesting the lower activity of the caudate is a permanent trait.

Activity is diminished in other parts of the stutterers’ brain as well, Wu said, but these all appear to be connected in some way to the caudate as a “central switchboard” in the brain’s left hemisphere. Parts of the frontal lobe responsible for planning and thinking, and other parts responsible for speech production all are hooked into the caudate. “What happens when someone stutters, we think, is this area of the brain, the caudate, is not able to properly tie in the thinking signals with the speech signals,” Wu said. “So . . . you can think of something to say, and start to say it, but because the switchboard is broken, the thinking signal doesn’t go through” to the parts controlling lip and tongue movements.

The research fits well with longstanding notions about the brain’s functions, Wu said. The left hemisphere has long been considered the “verbal” hemisphere, he said, while the right is more involved with processing nonverbal information. The findings suggest, as well, that the left caudate is connected to a part of the brain’s limbic system, which is involved in regulating anxiety.

“This limbic-caudate connection may explain why increased anxiety results in the worsening of stuttering symptoms,” the researchers wrote.

Researchers are not certain why the left caudate of stutterers behaves as it does. Wu said one theory is that the caudate might have an abnormally high level of the neurotransmitter dopamine, which tends to inhibit brain activity. In general, the caudate’s troubles appear to be genetic, researchers said, although brain injuries also can cause stuttering.

The researchers caution that their findings must be investigated further, because they are based on only four stutterers and four control subjects, who were not well-matched with the stutterers in age. Soon, the team will publish the results of scans on three more stutterers, including Maguire, which seem to support the original findings, Wu said.

Another question that remains to be answered is why stuttering is four times more common among men than women. Maguire said research in rats suggests that the major male sex hormone testosterone may cause abnormalities in caudate development. Wu said women may simply adapt better to brain defects in language processing.

The biggest question on stutterers’ minds, however, is what can be done to ease their condition.

“So we find some neat colored pictures,” Maguire said. “The question is, can we help anybody?”

Maguire is working on that too. He is getting ready to publish a study of a drug called nimodipine, traditionally used in the treatment of strokes. The drug improved the speech of four in 12 stutterers without the unpleasant side-effects of other stuttering medications, Maguire said.

He said it is possible that the drug works because it indirectly blocks dopamine’s effects in the brain.

The research team is adamant that speech therapy is important in the treatment of some stutters. Some can learn ways to get around the normal speech circuit, partially bypassing the caudate. They do this, for example, by slowing their speech or prolonging the beginning of words.

“It seems like any kind of deliberative speech can bypass it,” Wu said. “The caudate is more involved with automatic speech.”

Therapy also can help people “unlearn” some of the behaviors they develop to adapt to or hide their stuttering, researchers said.

Riley of Cal State Fullerton said many stutterers avoid certain words or entire situations--such as talking on the telephone--where they are likely to stutter. Others, as speech pathologist Ronayne suggested, develop tics, grimaces or arm movements that they believe helps them get words out.

The prognosis is particularly good for children, Ronayne said, especially if parents get them into early speech therapy. Many children, whose brains are more flexible than adults’, will outgrow stuttering or learn how to resolve it.

Stutterers familiar with the most recent research say it not only provides hope for treatment, it is a vindication of sorts. For years, they say, they have lived with misconceptions, reinforced by movies and television, that stutterers are somehow less balanced than those who speak fluently.

Though some said psychologists have said they suffered from unresolved anger, and employers have fired them for seeming to lack competence, many suspected, deep down, that their problem was basically physical.

“I’ve always felt it was neurological,” said Annie Bradberry, 36, of Corona, an administrator with the National Stuttering Project. “The idea that this is getting the attention it deserves and helping us to overcome those misconceptions is wonderful for the stuttering community.”

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Understanding Stuttering

Scientists have linked stuttering to a part of the brain called the caudate. In stutterers, the almond-size section, responsible for coordinating speech processes, is slow to transmit its signals. How speech is routed:

1) Frontal lobe: Plans and thinks of things to say.

2) Broca’s area: Instructs speech muscles how to move.

3) Caudate: “Switchboard” links thinking, motor skills.

4) Motor cortex: Orders speech muscles to move.

Source: UCI Brain Imaging Center

Researched by APRIL JACKSON / Los Angeles Times