“I wou-wou-wou-wou-would very much like to talk to y-y-ou all”. It’s not always the case that people with this problem always have enough self confidence to start a conversation or even to just participate in one. Already in childhood, many stutterers suffer an accumulated history of teasing. It’s a discrimination that continues into adulthood. Still, the background to, and often the cause of the lost ability to speak fluently, is unknown.
Speaking = teamwork in the brain
Larynx, palate, tongue, lips. Around 100 muscles are activated when speaking. The respiratory system controls the air we breathe, which first gives our voice the required volume. In the brain, various motor and sensory areas cooperate with fine control so as to achieve this precise interaction. Speaking itself is a constant interplay between the production of sounds and a feedback control of what leaves our mouths. When the fluid formulation of sentences falters and the speaker repeats the same syllables entirely unintentionally, then it could be, linguists say, related to a dysfunction in this feedback control.
“In the brain of people who stutter”, as Scott Grafton from the University of California describes, ” something is fundamentally different”. If one could know more about physiological causes and effects in the central nervous system, a therapy might be conceivable which intervenes directly in these cycles.
Stutterers sing without problems
For about 100 years, scientists have been wrangling with the issue. For a very long time, doctors concentrated initially only on the psychological aspects and sent all their patients, whether younger or older, to speech therapists, without asking about the causes. “Stuttering – a consequence of improper upbringing?”, many parents and psychologists wondered over a long time. Today, three basic situations are acknowledged in which speech fluency ceases to be: developmentally defined stuttering is the most common form of stuttering, and it often occurs in childhood. Stroke or brain trauma in contrast cause neurogenic stuttering, whereas traumatic experiences in the mind are responsible for a third form, a psychogenically conditioned stuttering.
Around one in twenty children between two and five years of age at sometime begin to stutter, in most cases fortunately this is only a temporarily state. Worldwide on average every hundredth person stutters, men being much more frequently afflicted than women. But even with stuttering adults the obstruction is not always present. When speaking in a foreign language or during singing, stammered utterings which would normally be present suddenly become fluent and smooth.
Right instead of left brain
Looking in particular at nerve bundles between different brain regions, these appear to be less distinct in stutterers than in fluent speakers. This matter relates in particular to the fasciculi between the language centres of the broca-areals in the prefrontal cortex, responsible for motor skills, and to Wernicke’s area in the temporal lobe, where hearing is processed. “In the majority of those stutterers studied, it seemed”, Scott Grafton says in outlining his findings derived from neuroimaging, “as though there is a neural connecting branch missing”. Several studies confirmed these abnormalities in both children and in adult permanent stutterers.
If such disruption in the connecting tracks already appears in children, then the big question remains: Why was the stuttering lost again over the growing up period and what is happening in the brain? Can such changes be induced even in the instance of permanent stuttering, in this way making fluent speakers out of stutterers?
Christian Kell of the University of Frankfurt (Germany) has studied children and adults who recovered from their articulation dysfunction. Whereas fluent speakers predominantly activate areas in the left hemisphere, this activity in people with previous or present articulation problems is balanced out, or the right hemisphere may be even more responsive when speaking. In doing so perhaps the brain attempts to compensate for deficiencies in transfer by shifting the respective processes to the other side of the brain. “To a certain degree, this can reduce the symptoms”, says Christian Kell, “but only in part, because the right brain does not really serve speaking functions”. Nevertheless, in convalescent stutterers things happen in the left half again more than was the case during the stuttering phase.
New techniques for better signal understanding
It seems that in those affected, not only do the connections within the brain not work as usual, but neither do the paths between the hemispheres. Failures, as studies using DTI (diffusion tensor imaging) show, also occur in the corpus callosum. Not only are the speed and bandwidth of the information flow probably crucial for fluent speech, but so too the exact sequence of activation of centres for language planning and motor execution. If the order of the incoming signals gets muddled up, such word-muddling ends up being the consequence.
Again and again, reports emerge about stuttering in otherwise-healthy individuals after a deep brain stimulation. One electrical stimulation of the thalamus used for chronic pains was indeed not effective against this condition, it did however produce reversible unwanted speech interruptions. In contrast, studies involving transcranial magnetic stimulation often show induction of motor signals to the tongue muscles and their further redirection from there. Here as well, experiments have shown that in normal speakers these signals come especially out of the left hemisphere, with stutterers however they usually come from both hemispheres equally.
New neural pathways: Cause or adaptation to inhibited fluency?
A number of factors speak in favour of there being a distinct genetic background with stuttering: the concordance in monozygotic twins is 63 percent, the fault often occurs with familial association. The unequal gender distribution suggests an influence of genetic information on the disturbed flow of language. The search for the relevant genes has proved quite costly and difficult. Coupling imbalances have been found with at least 10 chromosomes, but none of the described genes could be attributed an active role in the fluency outflow of speech. Depending on the examined collective, differing loci have been described.
One shortcoming in the previous studies is the fact that the objects of study were usually adults. With them, the signal pathways could have adapted to the neural deficit by using exit pathways and detours in other brain areas. With children, the situation would probably allow study closer to the point of origin of the disorder. It is still not yet clear whether the observed changes in the brain are the cause or consequence of speech obstruction. How does communication between the two hemispheres operate in fluent and less fluent speakers? That’s one of the questions to which the researchers still have no conclusive answer.
Pill against stuttering?
If we knew more about why it is that stuttering suddenly stops again in children, perhaps it would be possible, even with permanent stuttering adults, to building up the verbal outlets in a targeted manner by way of appropriate behavioural training. Or perhaps a simple pill against stuttering? Ever so often, reports surface stating that dopamine blockers are supposed to have a favourable effect on fluency. While actually having been prescribed for other ailments, they are said to have resulted in stuttering patients having a significant improvement in their speaking faculties. However, several studies have not been able to repeat this observation under controlled conditions and the number of cases in successful studies are small.
It may be, the authors of an overview article at the Leipzig Max Planck Institute for Human Cognitive and Brain Sciences in Germany speculate, that by using special hearing aids the maturing of faulty nerve connections between the helical, parietal and temporal lobe and the interplay between listening and speaking could be strengthened. If science can show even better in the future how the communication between many different areas in the brain works, and what happens as part of disorders, there would someday perhaps be no reason for stutterers to feel marginalised, suffering in addition to their neurological disorder other psychological stress as well.