Alison Ruth
August 6th, 2018
SPHSC 449
Compensatory strategies employed by stutterers right Hemisphere
The brain possesses a unique ability to reorganize synaptic connections in order to accommodate for injury or experience. This concept, known as neuroplasticity, provides an explanation for how changes in behavior and brain function can bring about changes in brain anatomy. ______ This has been observed across multiple studies involving the brains of individuals who stutter. ____ compensate for the speech disorder through rewiring neural networks and increasing grey matter volume in regions within the right hemisphere that can be utilized in speech.
Because relatively few studies have been conducted revolving around children who stutter, it has been challenging for researchers to accurately identify and differentiate between functional and anatomical differences in the brains of both child and adults with the disorder. Although it still remains difficult to immediately distinguish the brain of a child who stutters from the brain of a child with typical language, Chang et al. were able to identify subtle structural changes in the brains of stuttering children to help better determine how the speech disorder transforms the brain over time.
Stuttering can affect the brain in a variety of ways both functionally and anatomically. The brains of adults who stutter have been shown to exhibit differences in the perisylvian frontotemporal regions, atypical right-left asymmetries in the planum temporale, increased white matter volume in the right hemisphere (including the superior temporal gyrus), and reduced white matter integrity in the left inferior arcuate fasciculus linking the temporal and frontal areas (Chang et al., 2008). Researchers have identified stuttering as the root of abnormal activity in auditory association areas, and have also discovered that it is responsible for abnormal timing relationships between premotor and primary motor regions in the brain’s left hemisphere. Differences in activity within the right frontal and left cerebellar regions can also be attributed to changes brought about by stuttering (Chang et al., 2008).
Chang et al.’s study Brain Anatomy Differences in Childhood Stuttering examined brain structure differences between three groups of children. They compared the brains of children who stuttered, children who had recovered from preschool stuttering, and a group of age-matched children who served as fluent control subjects. Although asymmetries between brain hemispheres have been recorded in adult stutterers (Foundas et al., 2001), Chang et al. did not discover such differences in their child subjects. Adults who stutter usually display pronounced increases in right hemisphere speech areas, which can be attributed to a lifetime of stuttering leading their brains to develop compensatory strategies to accommodate for the disorder. The fact that the researchers were unable to find similar increases in right hemisphere speech areas in their subjects who stuttered “suggests that right hemisphere enhancement develops with continued stuttering into adulthood” (Chang et al., 2008). The many years spent rewiring the brain to compensate for disfluency helps explain why the brains of adult stutterers demonstrate more significant transformations within their right hemispheres as compared to children. It can be hypothesized that increases in right hemisphere white and gray matter become more pronounced further out from the onset of stuttering.
Although the dramatic anatomical differences observed in adult stutterers’ right hemispheres were not exhibited in the child subjects, researchers found that the children’s brains “demonstrated reduced volume in several left side structures, including Brodmann’s area and the superior temporal gyrus” (Chang et al., 2008). These gray matter volume results in childhood differ from previous findings in adults who stutter that showed bilateral increases in the planum temporale and atypical right to left asymmetry (Foundas et al., 2001). Overall, however, the lifelong use of right-side mechanisms for speech leads to a reduction in asymmetry across both brain hemispheres in adults.
Some researchers have found right sided increases both during speech production and other tasks, suggesting that greater right hemisphere activation may be inherent in adults who stutter (Preibisch et al., 2003)
Differences in gray and white matter volume were discovered in the children who had experienced any form of stuttering in their preschool years, regardless of whether they had recovered from it or not (Chang et al., 2008). The researchers found that white matter integrity “was reduced underlying the left rolandic operculum, which overlaps the oral-facial motor regions in the left hemisphere” (Sommer et al., 2002). This anatomical difference is also observed in adult stutterers, suggesting that this decrease is a defining feature of individuals who stutter (Chang et al., 2008).
Chang et al.’s findings reveal the role of neuroplasticity throughout development in
Increases in gray matter volume can occur following years of motor training, practice with musical instruments, or the acquisition of proficiency in a second language. Asymmetries in brain structure can also arise as a result of handedness, which is why researchers control for hand dominance in most studies involving individuals who stutter.
Functional neuroimaging studies of connected speech in stuttering speakers have shown disparity in the level and extent of activation between the left and right hemispheres in the motor and auditory regions (Braun et al., 1997, Fox et al., 1996, Neumann, 2007). Some differences include over-activation in the right frontal operculum and insula during both stuttered and fluent speech production (Braun et al., 1997, Fox et al., 2000), decreased activation in auditory association areas in the temporal lobe during stuttering (Braun et al., 1997, Fox et al., 1996), and increased motor and cerebellar activation during speech production (Braun et al., 1997, Fox et al., 2000).
References
Chang, S., Ph.D., Erickson, K. I., Ph.D., Ambrose, N. G., Ph.D., Hasegawa-Johnson, M. A., Ph.D., & Ludlow, C. L., Ph.D. (2008, February 1). Brain Anatomy Differences in Childhood Stuttering. In National Center for Biotechnology Information. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2731627/
Preibisch, C., Neumann, K., Raab, P., Euler, H. A., Von Gudenberg, A. W., Lanfermann, H., & Giraude, A. (2003, June 12). Evidence for Compensation for Stuttering by the Right Frontal Operculum. In Science Direct. Retrieved from https://ac.els-cdn.com/S1053811903003768/1-s2.0-S1053811903003768-main.pdf?_tid=e26e5045-4b52-4a06-9af0-60aa99602d1e&acdnat=1533527990_96623f8cd043b3fd626c42ddf6ead083
Chang, S., Ph.D. (2016, October 3). Research Updates in Neuroimaging Studies of Children Who Stutter. In National Center for Biotechnology Information. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5046827/
Sommer, M., Koch, M. A., Paulus, W., Weiller, C., & Büchel, C. (2002, August 3). Disconnection of speech-relevant brain areas in persistent developmental stuttering. In The Lancet. Retrieved from https://ac.els-cdn.com/S0140673602096101/1-s2.0-S0140673602096101-main.pdf?_tid=ca4c4e19-0252-4e8d-ab3f-bc10b3462ae5&acdnat=1533533461_32c6010c410f5b5615dc69fb3285eb65
Foundas AL, Bollich AM, Corey DM, Hurley M, Heilman KM. (2001). Anomalous anatomy of speech-language areas in adults with persistent developmental stuttering. In PubMed. Neurology.