Stuttering and the Basal Ganglia Circuits a Critical Review of Possible Relations

By Per Alm, Ph.D., University of Alberta
Winter 2006

Editor's note: Per Alm has a Ph.D. in neuropsychology and has been working with research on stuttering in Sweden simply is currently teaching at the University of Alberta, Edmonton. We asked Per if he could write something about his research and his view on stuttering and the brain.

The variability of stuttering is oftentimes striking to the listener and mysterious for the person who stutters.

Based on personal experiences I have felt that the lack of real noesis virtually the underlying mechanisms of stuttering is a problem in many ways. It makes information technology more hard to treat, information technology leaves the field open up to unfounded speculations, and information technology makes it difficult for persons who stutter to reach self-understanding. For this reason, I changed my vocation from engineering to research on the nature of stuttering, well-nigh 10 years ago.

When I began my Ph.D. studies, it was not piece of cake to know what to do to advance the understanding of stuttering. So many ingenious efforts had already been fabricated. Comparing this research to a puzzle, information technology felt important to try to make sense of the scattered pieces. Therefore I worked both with experimental studies and theoretical overviews of previous enquiry findings.

In this commodity I will focus on the main theoretical work, regarding the possible relation between stuttering and the basal ganglia, brain structures involved in automatization (Alm, 2004). This work led to the proposal of the dual premotor systems model of stuttering (Alm, 2005). The idea that stuttering is related to the basal ganglia is not new. The starting time account came from the German physician Sahli, based on studies of epidemic encephalitis around 1920. Among afterwards examples can be mentioned Caruso (1991) and Molt (1999).

Conditions where stuttering tends to be absent provide important clues nearly the underlying dysfunction. I such condition is the "rhythm effect": persons who stutter unremarkably become fluent when speaking to the pace of a metronome. They seem unable to stutter when following the beats. This distinction, to have a problem performing a motor sequence on your own, just being able to practise it when receiving external "timing cues," is characteristic of dysfunction of the basal ganglia motor circuits (including related structures, such as the supplementary motor expanse (SMA)). Normally, the basal ganglia seem to provide "go-signals" for the segments in a motor sequence, e.chiliad. the syllables in voice communication.

Without sufficiently strong go-signals the speech cannot be started or volition exist disrupted. The rhythm result appears to be a central characteristic of stuttering, providing a strong indication that stuttering is related to some type of disturbance of the basal ganglia motor circuits.

In that location are several other indications for the important role of the basal ganglia in stuttering, for case: (1) Lesions that crusade "acquired stuttering" often affect the basal ganglia (Ludlow et al., 1987). (2) The drugs that have shown the clearest upshot on stuttering, to arrive ameliorate or worse, impact the dopamine organization. Dopamine is a fundamental transmitter that regulates the function of the basal ganglia. (iii) Basal ganglia motor disorders characteristically worsen during stress and "nervous tension," and improve under relaxed conditions.

In the review on stuttering and the basal ganglia (Alm, 2004), it was also argued that the typical pattern of onset of stuttering around age 2.5 to three, with a large percent of early recoveries, may exist related to a natural phase of the evolution of the basal ganglia. Specifically, information technology has been shown that children in general have a summit in the number of dopamine receptors type D2 in the basal ganglia at this fourth dimension. There are theoretical arguments for how a large number of D2 receptors may increase the risk for stuttering.

Furthermore, the drugs that have shown the best documented consequence on stuttering human action past blocking these D2 receptors. The number of D2 receptors has also been reported to evidence correlation with cognitive performance, which is in accord with the observation that children with early onset of stuttering often display precocious language development (Watkins, Yairi, & Ambrose,
1999).

In the thesis, On the causal mechanisms of stuttering (Alm, 2005), the basal ganglia model was developed further, based on the theoretical piece of work on the human motor system proposed past Goldberg (1985, 1991) and others.

Goldberg argued that the human brain has two parallel premotor systems, i.due east. systems involved in planning and execution of movements, including voice communication. (However, he did non discuss stuttering.) Co-ordinate to this model, both systems take the power to provide go-signals for movements, but under somewhat different weather. The lateral system, consisting of the lateral premotor cortex and the cerebellum, is agile when the movement is controlled in relation to the sensory input — similar when speaking to the pace of a metronome or reading in unison. Similarly, the lateral system is dominant when speech is controlled by auditory or somatosensory feedback.

In contrast, the medial system, consisting of the basal ganglia and the SMA, operates based on automatized programs without external feedback. This system is dominant during spontaneous speech, especially if the speech is propositional, i.e. that it conveys thoughts or emotions.

The lateral system is besides assumed to be agile when a motility is executed with increased attending and conscious control, while the medial system dominates for automatic responses. This is claimed to exist the reason why information technology is difficult to get a natural smile when asked by a photographer — voluntary and spontaneous smiles are created by two dissimilar systems in the brain. This distinction suggests that the lateral arrangement is in charge when speaking in a way that is not automatic, like imitating an emphasis or playing a role.

This dual premotor systems model of stuttering provides a novel explanation for most of the well-known fluency inducing weather in stuttering. Stuttering is related to a disturbance of the medial system, but when the control is shifted from the medial to the lateral organization the problem is bypassed. As mentioned above, this could pertain to the metronome effect, unison reading, imitation of an accent, and role play. Furthermore, there are research data supporting that it is the lateral system that is dominant for go-signals during singing and rhythmic speech, conditions know to  better fluency.

An interesting question is how the effect of altered auditory feedback on stuttering tin be explained, for example frequency contradistinct feedback (FAF). There are now several encephalon imaging studies showing specific activation of the lateral premotor arrangement when listening to speech sounds. Moreover, recent encephalon imaging data (Watkins, Davis, & Howell, 2005) have shown increased activation of the auditory cortex during speech with FAF. These findings point to increased control from the lateral organisation during altered feedback, so that difficulties with the medial organisation may be bypassed. This hypothesis is supported by reports that some speech difficulties in Parkinson's affliction, which is a basal ganglia disorder, may be improved by either delayed or frequency altered auditory feedback.

An of import aspect of the dual premotor model is that information technology emphasizes that the basal ganglia system is office of a larger medial system, including the complete loop from the cortex through the basal ganglia and the thalamus, and back to the cortex (the SMA). For example, equally suggested in Alm (2004), the product of get-signals from the basal ganglia may exist disturbed because of deficient input from the primary motor cortex. In this way the basal ganglia model is compatible with the contempo reports of structural anomalies of the cortex and the white matter, e.one thousand. in the sensorimotor region for the speech organs (Foundas et al., 2001; Sommer et al., 2002; Jancke et al., 2004;
Watkins et al., 2005). A more detailed business relationship of this dual premotor model of stuttering is currently nether way.

A pdf-file of the thesis can exist downloaded from http://theses.lub.lu.se/postgrad/ (Yet, the online version does not yet include all the enquiry papers, because of copyright questions. For missing papers contact Per.Alm@psychology.lu.se . Printed copies of the complete thesis can be ordered from the Swedish Stuttering Association, kansliet@stamning.se , maybe about $20 including stamp.)

References
Alm, PA (2004). Stuttering and the basal ganglia circuits: a critical review of possible relations. Journal of Communication Disorders, 37, 325-69.
Alm, PA (2005). On the causal mechanisms of stuttering. Doctoral thesis. Dept. of Clinical Neuroscience, Lund University, Sweden.
Caruso, AJ (1991). Neuromotor processes underlying stuttering. In Peters et al. Speech motor control and stuttering (101-16).
Foundas, AL et al. (2001). Anomalous anatomy of speech-language areas ... Neurology, 57, 207-15.
Goldberg, One thousand (1985). Supplementary motor area ... Behavioral Encephalon Sci, 8, 567-616.
Goldberg, G (1991). Microgenetic theory and the dual premotor systems hypothesis. In Hanlon Cerebral microgenesis (32-52).
Jancke, 50 et al. (2004). Morphological brain differences ... BMC Neurology, 4.
Ludlow, CL et al. (1987). Site of penetrating brain lesions ... Ann Neurol, 22, sixty-six.
Molt LF (1999). The basal ganglia's possible role in stuttering. Proc. 2d Internat. Stuttering Awareness Solar day, Internet.
Sommer, K et al. (2002). Disconnection of speech-relevant brain areas ... Lancet, 360, 380-3.
Watkins, M, Davis, One thousand, & Howell, P (2005). Brain activity during altered auditory feedback. Paper at the Oxford Dysfluency Conference 2005, Oxford.
Watkins, RV, Yairi, E, & Ambrose, NG (1999). Early childhood stuttering 3. J Speech Lang Hear Res, 42, 1125-35.

To print this commodity, offset download the PDF.

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Source: https://www.stutteringhelp.org/stuttering-and-basal-ganglia

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