Atypical somatosensory-motor cortical response during vowel vocalization in spasmodic dysphonia.

• Inhibition of slow motor cortical rhythms during vocalization is reduced in spasmodic dysphonia. • Somatosensory-motor cortical synchrony during vocalization is excessive in spasmodic dysphonia. • Abnormal cortical processing in spasmodic dysphonia is mainly lateralized in the left hemisphere. Spasmodic dysphonia (SD) is a debilitating voice/speech disorder without an effective cure. To obtain a better understanding of the underlying cortical neural mechanism of the disease we analyzed electroencephalographic (EEG) signals of people with SD during voice production. Ten SD individuals and 10 healthy volunteers produced 50 vowel vocalization epochs of 2500 ms duration. Two EEG features were derived: (1) event-related change in spectral power during vocalization relative to rest, (2) inter-regional spectral coherence. During early vocalization (500–1000 ms) the SD group showed significantly larger alpha band spectral power over the left motor cortex. During late vocalization (1000–2500 ms) SD patients showed a significantly larger gamma band coherence between left somatosensory and premotor cortical areas. Two atypical patterns of cortical activity characterize the pathophysiology of spasmodic dysphonia during voice production: (1) a reduced movement-related desynchronization of motor cortical networks, (2) an excessively large synchronization between left somatosensory and premotor cortical areas. The pathophysiology of SD is characterized by an abnormally high synchronous activity within and across cortical neural networks involved in voice production that is mainly lateralized in the left hemisphere. [ABSTRACT FROM AUTHOR]