Laryngeal reaction time profiles in spasmodic dysphonia: relationship to cortical electrophysiologic abnormality

This study combines measures of linguistic and vocal performance and long-latency auditory electrophysiology to investigate task-dependent variability in spasmodic dysphonia (SD). Linguistic performance was evaluated using several measures of relatively complex linguistic ability (i.e., discourse analysis). Vocal performance was evaluated by measuring acoustic laryngeal reaction time (LRT) for tasks that differ in complexity. Normal structure of the cortex and subcortex was confirmed by magnetic resonance imaging. Cortical function was measured using multichannel quantitative auditory evoked potentials (AEPs). As a group, SD subjects who demonstrated subtle linguistic deficits also demonstrated prolonged LRT for the complex task and repeated and persistent auditory electrophysiologic abnormalities over the anterior quadrant of the left hemisphere. As a group, linguistically normal SD subjects demonstrated no significant increase in LRT for the complex task and no recurrent electrophysiologic abnormalities over the left anterior cortex relative to normal controls. Results support a neurogenic origin of SD and suggest that some aspects of inter- and intrasubject variability may be related to differences in loci and magnitude of cortical abnormalities.