Abnormal motor cortex excitability during linguistic tasks in adductor-type spasmodic dysphonia

Area of Science:

• Neuroscience
• Speech Pathology
• Motor Control

Background:

• Adductor-type spasmodic dysphonia (ASD) is a focal dystonia affecting speech production.
• Transcranial magnetic stimulation (TMS) reveals cortical excitability changes during linguistic tasks in healthy subjects (HS).
• Investigating these changes in ASD patients can elucidate the neurophysiological underpinnings of the disorder.

Purpose of the Study:

• To investigate linguistic task-related cortical excitability modulation in the dominant hemisphere's primary motor cortex (M1) in ASD patients.
• To compare excitability patterns between ASD patients and HS during various linguistic and non-linguistic tasks.
• To assess the effect of botulinum neurotoxin-type A (BoNT-A) treatment on neurophysiological abnormalities in ASD.

Main Methods:

• TMS was used to measure motor evoked potentials (MEPs) and cortical silent period (CSP) in the dominant M1 of 10 ASD patients and 10 HS.
• Participants performed linguistic (reading aloud, silent reading, phonation) and non-linguistic tasks.
• MEPs were also recorded during hand-related action-verb observation, and patients were studied with and without BoNT-A treatment.

Main Results:

• HS showed increased M1 excitability during 'reading aloud' compared to other tasks.
• ASD patients exhibited increased M1 excitability during 'reading aloud' and 'syllabic phonation' tasks.
• CSP was shorter in ASD patients, and MEPs increased during action-verb observation in ASD, unlike in HS. BoNT-A treatment normalized these findings.

Conclusions:

• ASD is associated with altered dominant hemisphere cortical excitability during linguistic tasks.
• These neurophysiological abnormalities are distinct from those in HS and are modulated by speech-related actions.
• BoNT-A treatment effectively ameliorates speech symptoms and restores normal TMS-derived excitability patterns in ASD.