Stuttering Essay Research Paper Recent brain scan

Stuttering Essay, Research Paper

Recent brain scan research has found abnormalities in the brains of stutterers, and promises new treatments for stuttering using drugs and computerized devices.

No differences between stutterers and non-stutterers have been found during silent rest (Ingham, 1996). During fluent speech, stutterers’ brains look similar to non-stutterers’ brains.

But during stuttering, cerebral activity changes dramatically. The most striking difference is that left-hemisphere areas active during normal speech become less active, and areas in the right hemisphere not normally active during speech become active (Braun, 1997; Ingham, 1997).

This abnormal right-hemisphere dominance has produced a variety of speculative hypotheses from researchers. Note that brain scans can show relative activity in different areas of the brain, but can’t show what the person is thinking or what each area is doing. Researchers often hypothesize on the functions of various brain areas, but this is at best educated speculation.

One hypothesis is that there is something wrong with stutterers’ left-brain speech areas, and so right-brain areas not developed for speech take over. This seems unlikely, given that most stutterers are capable of normal, fluent speech in some conditions.

Another hypothesis is that the right-hemisphere activity is the fears and anxieties that stutterers experience, generated by the limbic and paralimbic structures. But these areas don’t seem to be abnormally active during stuttering.

Another hypothesis is base on the decreased central auditory processing during stuttering seen in all studies (Wu, 1995; Fox, 1996; Ingham, 1997). One study also found decreased activity in the area that integrates auditory and somatic (body) sensation (Braun, 1997). These are all rear-brain areas. The researchers hypothesized that stuttering reduces this rear-brain sensory processing, and reduces the left-brain communication of this sensory information to frontal speech and language areas. The abnormal right-brain activity may be an alternative pathway for rear-brain sensory information to travel to the front of the brain.

Another team of researchers believes that the key to stuttering lies in the different functions of the lateral and medial systems (Goldberg, 1985; Maguire, 1997). The lateral system is part of the cortex, where our consciousness is, and we have conscious awareness and control of lateral functions. This area produces and understands language (Wernicke’s area), forms words (Broca’s area), and forms muscle movements (supplementary motor areas). These areas can produce speech under closed-loop motor control. Even severe stutterers can speak fluently under closed-loop motor control, but high attention demands and abnormally-slow speech (Shea, 1993) make this an undesirable way to talk. Another closed-loop motor activity is threading a needle — and talking under closed-loop motor control takes as much attention and is as slow as threading a needle.

The medial or striatal system produces open-loop or normal speech. This system includes the caudate and putamen. Preprogrammed motor programs are retrieved from long-term memory and executed, without sensory feedback. Open-loop control can produce rapid movements, with little or no attention. The disadvantage is that there’s no error regulation — if your speech motor programs contain stuttering, you’ll continue stuttering rather than correct your speech. Open-loop motor control responds to stimuli, without conscious thought. Stutterers can speak fluently in certain situations, such as speaking to a pet, but when they experience stimuli such as time pressure or speak to an authority figure, their medial systems pull stuttering speech motor programs from long-term memory.

Stutterers have decreased medial system activity during both stuttering and fluent speech (chorus reading). They have decreased lateral system activity during stuttering, and increased lateral activity during fluent speech (Wu, 1997).

Glyndon Riley, Joseph Wu, and Gerald Maguire (1997) propose that the medial system is affected by the D2 dopamine modulation system. This includes the substantia nigra and its circuit to the striatum. Dopamine is the neurotransmitter that produces alertness, motivation, and mental acuity. In stutterers, excess dopamine may reach the striatum and reduce activation, making these areas less effective.

The dopamine system may explain why stutterers have “good days,” when they easily speak fluently, and “bad days,” when they can’t get a word out without a hard block. Dopamine levels vary with diet and other factors.

A study of three genes that control dopamine in persons with Tourette’s Syndrome and their relatives found that these genes correlate with attention deficit hyperactive disorder (ADHD), stuttering, and Tourette’s Syndrome (Comings, 1996).

Riley, Wu, and Maguire point out that stuttering therapy works almost entirely with the lateral system, teaching stutterers to consciously control their speech, stuttering behaviors, and/or feeling and attitudes. The result too often is fluency in the speech clinic, when the stutterer is paying close attention to his speech, but when he returns to his usual environmental, cues to stutter cause him to lose control of his speech.

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