The Stuttering Brain
By: Mona Tong, '18
(CHAOS 2016 EDITION)
(CHAOS 2016 EDITION)
Stuttering is still considered to be a relatively understudied topic among scientists. Many questions about stuttering remain unanswered, and much of the research and data collected still remains undeciphered.
Stuttering is a neurobiological disorder, characterized by an involuntary repetition or drawing out of sounds or words. It occurs in about 5% of young children between ages two through seven, and the stutter usually goes away before puberty. However, in the 1% of developmental stutterers in the world, the stutter persists after puberty, or may even get worse, over time. Developmental stuttering stems from genetic roots, and is then further influenced by neurological changes and differences in the brain. Persistent developmental stuttering generally runs in families, and one identical twin has a 77% greater chance of stuttering if the other twin stutters, demonstrating that stuttering is genetically-related.
However, subsequent neurological factors also affect stuttering. A PET scan conducted in 1996 at the University of Texas at San Antonio presented significant differences between developmental stutterers and non-stutterers. The study showed that stutterers exhibited lower activity in the speech and auditory areas in the left side of the brain and higher activity in motor areas, the cerebrum, and the cerebellum in the right hemisphere. In contrast, non-stutterers displayed the opposite (higher activity in the left hemisphere, in speech and auditory areas, and lower activity in the right hemisphere, in motor areas). Thus, as opposed to non-stutterers who displayed left hemisphere dominance, stutterers exhibited right hemisphere dominance.
According to studies conducted in the University of Texas at San Antonio in 2004, stutterers also exhibited an abnormal neural processing sequence, in comparison to non-stutterers. In non-stutterers, the processing sequence went from the Broca’s area, which is associated with left hemispheric speech production and articulation, to the motor areas. On the other hand, the stutterer’s brain reversed this sequence, going from the motor areas, to the Broca’s area. Studies at University of California at Santa Barbara in 2015 indicated missing parts and reduced integrity in the arcuate fasciculus, a white matter pathway. The arcuate fasciculus is established in the scientific community, to play a critical role in producing normal speech. Damages or lesions and missing parts to it are thought to contribute towards stuttered speech, as well as many other acquired speech disorders.
Little is known about treatment and natural compensation/recovery from stuttering. In general, stuttering is thought to be treatable, but incurable. Interestingly, stutterers stutter less when singing or in chorus readings. Although an exact and accepted answer has not been found, there are some hypotheses. When a stutterer speaks fluently, they may be using, or even just slightly activating, alternate speech pathways. Scientists have yet to find out what exactly these “alternate speech pathways” include. It is also hypothesized that over-activations in the right hemisphere of the brain may compensate for stuttering.
Brain scans conducted at the University of Texas at San Antonio in 2004 showed that when stutterers imagined stuttering, abnormalities appeared on the scan. These abnormalities included an abnormal activation in areas for speech planning, and an atypical deactivation in areas for auditory processing, speech monitoring, and articulatory movement planning. However, when the stutterers imagined speaking clearly and fluently, these regions in the brain scans normalized. This suggests that brain circuits may be already wired for stuttering before speech execution even takes place. I think that this finding should be delved into more, because I see it as an opening passage to create ways to rewire these circuits, through psychological therapy.
Moreover, there are essential differences between males and females in stuttering. For example, there are more male-stutterers than female stutterers (3:1 ratio), and females generally have a higher probability to recover than males. The reasons for these differences are unknown, but research has also gathered differences in brain structure between males and females, that may begin to open the doors to plausible answers. Research from the University of Texas at San Antonio in 2014 has found that female brains are more generally more bilateral, while male brains are more left-lateralized, and females also tend to have a larger Broca’s area than males by 20-30%. Furthermore, female stutterers tended to have a lower cerebellum/motor activity than male stutterers. Interestingly, this characteristic is more similar to non-stutterers, as non-stutterers tend to exhibit a higher activity in in speech and auditory areas, and lower activity the cerebrum, cerebellum, and motor areas, than stutterers. Research has yet to expand upon the differences between male and female stutterers and why these differences occur.
Stuttering is a neurobiological disorder, characterized by an involuntary repetition or drawing out of sounds or words. It occurs in about 5% of young children between ages two through seven, and the stutter usually goes away before puberty. However, in the 1% of developmental stutterers in the world, the stutter persists after puberty, or may even get worse, over time. Developmental stuttering stems from genetic roots, and is then further influenced by neurological changes and differences in the brain. Persistent developmental stuttering generally runs in families, and one identical twin has a 77% greater chance of stuttering if the other twin stutters, demonstrating that stuttering is genetically-related.
However, subsequent neurological factors also affect stuttering. A PET scan conducted in 1996 at the University of Texas at San Antonio presented significant differences between developmental stutterers and non-stutterers. The study showed that stutterers exhibited lower activity in the speech and auditory areas in the left side of the brain and higher activity in motor areas, the cerebrum, and the cerebellum in the right hemisphere. In contrast, non-stutterers displayed the opposite (higher activity in the left hemisphere, in speech and auditory areas, and lower activity in the right hemisphere, in motor areas). Thus, as opposed to non-stutterers who displayed left hemisphere dominance, stutterers exhibited right hemisphere dominance.
According to studies conducted in the University of Texas at San Antonio in 2004, stutterers also exhibited an abnormal neural processing sequence, in comparison to non-stutterers. In non-stutterers, the processing sequence went from the Broca’s area, which is associated with left hemispheric speech production and articulation, to the motor areas. On the other hand, the stutterer’s brain reversed this sequence, going from the motor areas, to the Broca’s area. Studies at University of California at Santa Barbara in 2015 indicated missing parts and reduced integrity in the arcuate fasciculus, a white matter pathway. The arcuate fasciculus is established in the scientific community, to play a critical role in producing normal speech. Damages or lesions and missing parts to it are thought to contribute towards stuttered speech, as well as many other acquired speech disorders.
Little is known about treatment and natural compensation/recovery from stuttering. In general, stuttering is thought to be treatable, but incurable. Interestingly, stutterers stutter less when singing or in chorus readings. Although an exact and accepted answer has not been found, there are some hypotheses. When a stutterer speaks fluently, they may be using, or even just slightly activating, alternate speech pathways. Scientists have yet to find out what exactly these “alternate speech pathways” include. It is also hypothesized that over-activations in the right hemisphere of the brain may compensate for stuttering.
Brain scans conducted at the University of Texas at San Antonio in 2004 showed that when stutterers imagined stuttering, abnormalities appeared on the scan. These abnormalities included an abnormal activation in areas for speech planning, and an atypical deactivation in areas for auditory processing, speech monitoring, and articulatory movement planning. However, when the stutterers imagined speaking clearly and fluently, these regions in the brain scans normalized. This suggests that brain circuits may be already wired for stuttering before speech execution even takes place. I think that this finding should be delved into more, because I see it as an opening passage to create ways to rewire these circuits, through psychological therapy.
Moreover, there are essential differences between males and females in stuttering. For example, there are more male-stutterers than female stutterers (3:1 ratio), and females generally have a higher probability to recover than males. The reasons for these differences are unknown, but research has also gathered differences in brain structure between males and females, that may begin to open the doors to plausible answers. Research from the University of Texas at San Antonio in 2014 has found that female brains are more generally more bilateral, while male brains are more left-lateralized, and females also tend to have a larger Broca’s area than males by 20-30%. Furthermore, female stutterers tended to have a lower cerebellum/motor activity than male stutterers. Interestingly, this characteristic is more similar to non-stutterers, as non-stutterers tend to exhibit a higher activity in in speech and auditory areas, and lower activity the cerebrum, cerebellum, and motor areas, than stutterers. Research has yet to expand upon the differences between male and female stutterers and why these differences occur.
Works Cited:
Cieslak, M., Ingham, R., Ingham, J., & Grafton, S. (2015). Anomalous White Matter Morphology in Adults Who Stutter. Journal of Speech Language and Hearing Research, 58, 268-277.
Finn, E. (2011, May 18). Ask a Geneticist. Retrieved October 6, 2015, from http://www.genetics.thetech.org/ask/ask410
Fox, P., Ingham, R., Ingham, J., Hirsch, T., Downs, J., Martin, C., . . . Lancaster, J. (1996). A PET study of the neural systems of stuttering. Nature. Retrieved October 20, 2015, from http://www.ncbi.nlm.nih.gov/pubmed/8700204
Imaging Studies Make a Case for the Brain Basis of Stuttering. (n.d.). Retrieved October 12, 2015, from https://www.mnsu.edu/comdis/kuster/harkness1.html
Ingham, R., Fox, P., Ingham, J., Xiong, J., Zamarripa, F., Hardies, L., & Lancaster, J. (2004). Brain Correlates of Stuttering and Syllable Production. Journal of Speech Language and Hearing Research, 47, 321-341.
Smith, B. (2015, February 24). Brain structure linked to stuttering. Retrieved October 27, 2015, from http://www.redorbit.com/news/health/1113340185/brain-structure-linked-to-stuttering-022415/
Cieslak, M., Ingham, R., Ingham, J., & Grafton, S. (2015). Anomalous White Matter Morphology in Adults Who Stutter. Journal of Speech Language and Hearing Research, 58, 268-277.
Finn, E. (2011, May 18). Ask a Geneticist. Retrieved October 6, 2015, from http://www.genetics.thetech.org/ask/ask410
Fox, P., Ingham, R., Ingham, J., Hirsch, T., Downs, J., Martin, C., . . . Lancaster, J. (1996). A PET study of the neural systems of stuttering. Nature. Retrieved October 20, 2015, from http://www.ncbi.nlm.nih.gov/pubmed/8700204
Imaging Studies Make a Case for the Brain Basis of Stuttering. (n.d.). Retrieved October 12, 2015, from https://www.mnsu.edu/comdis/kuster/harkness1.html
Ingham, R., Fox, P., Ingham, J., Xiong, J., Zamarripa, F., Hardies, L., & Lancaster, J. (2004). Brain Correlates of Stuttering and Syllable Production. Journal of Speech Language and Hearing Research, 47, 321-341.
Smith, B. (2015, February 24). Brain structure linked to stuttering. Retrieved October 27, 2015, from http://www.redorbit.com/news/health/1113340185/brain-structure-linked-to-stuttering-022415/