Ch. 7: Is Stuttering Biological?

Question 1

Studies

Answer 1

See PowerPoint (Slides 2-8)

Question 2

Recent evidence from linkage studies (Kang et al. 2010)

Answer 2

• Significant linkage on chromosome 12
• Three relevant gene mutations identified (GNPTAB, GNPTG, and NAGPA)
• Mutations associated with lysosomal storage disorders

Question 3

What might be transmitted?

Answer 3

• Structural anomalies?
• Biochemical pathways?
• Brain processing?
• Motor skills?
• Temperament?

Question 4

MRI morphometry (Based on Foundas, et al., 2001)

Answer 4

Note extra-gyri in the Sylvian fossa of the stutterer

Question 5

Cerebral Dominance Theory

Answer 5

• Proposed stuttering was caused by a lack of cerebral dominance
• Left and right hemispheres compete for control of speech movements
• Asynchrony (mistiming) of neural impulses from both sides of the brain disrupts speech fluency

Question 6

Recent evidence from linkage studies (Kang et al. 2010)

Answer 6

• Significant linkage on chromosome 12
• Three relevant gene mutations identified (GNPTAB, GNPTG, and NAGPA)
• Mutations associated with lysosomal storage disorders

Question 7

Differences in brain structure

Answer 7

• Wernicke’s area smaller in LH for PWS
• More gyri in Sylvian (LH) region in PWS
• Higher white matter volume in RH
• Reduced white matter integrity in LH
• Deficiencies in LH gray matter volume
• *Most research done w/ adults!

Question 8

Recent research with kids…

[Chang et al., 2008]

Answer 8

• Reduced white matter integrity in LH
• Persistent and Recovered CWS: lower gray matter volume in LH speech areas
• But…only CWS who persisted showed lower white matter integrity in LH
• No differences in RH activity and no asymmetry between hemispheres.

Question 9

Neuro-physiologicaldifferences

Answer 9

• Overactivation of motor areas
  
  • Especially in RH
• Lower activity in auditory areas
  
  • Auditory suppression bilaterally
• Anomalous RH activity and lateralization
• Decreased connectivity of white matter
• Lower activity in basal ganglia and cerebellum
• More activation in anterior cingulated cortex

Question 10

Auditory Perceptual Theory

Answer 10

• Proposed stuttering was caused by defective auditory feedback
• The speaker expects to hear sound earlier than their auditory system feeds it back
• The speaker waits (prolongs) or repeats trying to correct the delay

Question 11

Role of audition

Answer 11

• Speech control relevant to audition
  
  • Deaf individuals
  • The Lombard effect
  • Delayed Auditory Feedback
  • Frequency Altered Feedback
• Dichotic listening studies

Question 12

Systems in the Regulation of Movement

Answer 12

See PowerPoint

Question 13

Sensory/Motor Dysfunction

Answer 13

• Most obvious part of stuttering
• Slower response times (vocal or manual)
• Abnormal movement patterns in jaw, tongue, and larynx (even in fluent speech)
  
  • E.g., timing, muscle activation sequencing force of movements, abnormal breathing patterns, slower rate

Question 14

Brainstem Reflexes: Disorder of Movement Theory

Answer 14

• Proposed stutterers have reduced tolerance for a range of oral movements
• If the range is exceeded, brainstem reflex management is upset
• Afferent and efferent signals of speech muscles conflict so stuttering occurs

Question 15

DIVA (Directions into Velocities of Articulators) Model

Answer 15

• Stuttering is due to a disorder of sensorimotor speech control
• PWS have unreliable FEEDFORWARD systems so they rely excessively on controlling speech via feedback
• Fluency is disrupted by the attempts to adjust speech movements after commands have been issued

Question 16

Conclusions??

Answer 16

• Is stuttering an impairment in the vocal organism itself (peripheral nervous system)?
• Or, it is a problem of vocal planning and initiation (central nervous system)?
• *Think about the ameliorating conditions
• RH overactivity may be compensatory

Question 17

Putting it all together…

Answer 17

Genetic and neurological research combined with sensory-motor dysfunctions in PWS point to a UNSTABLE/UNRELIABLE neuromotor system for speech

Question 18

But, don’t be depressed

Answer 18

• Plasticity of the brain is possible
• Many children develop a workaround (Chang et al. 2008)
• Following treatment, stronger left hemisphere activity
• Also, gray matter volume can increase with practice of certain behaviors