Reduced speaking-induced suppression of auditory evoked-potentials in early Parkinson’s disease suggests deficits in monitoring self-produced speech
ObjectiveSpeech deficits are common in Parkinsons disease, and behavioural findings suggest that the deficits may be due to impaired monitoring of self-produced speech. The neural mechanisms of speech deficits are not well understood. We examined a well-documented electrophysiological correlate of speech self-monitoring in patients with Parkinsons disease and control participants. MethodsWe measured evoked electroencephalographic responses to self-produced and passively heard sounds (/a/ phonemes) in age-matched controls (N=18), and Parkinsons disease patients who had minor speech impairment, but reported subjectively experiencing no speech deficits (N=17). ResultsDuring speaking, auditory evoked activity 100 ms after phonation (N1 wave) was less suppressed in Parkinsons disease than controls when compared to the activity evoked by passively heard phonemes. This difference between the groups was driven by increased amplitudes to self-produced phonemes, and reduced amplitudes passively heard phonemes in Parkinsons disease. ConclusionsThe finding indicates that auditory evoked activity is abnormally modulated during speech in Parkinsons patients who do not subjectively notice speech impairment. This mechanism could play a role in producing speech deficits in as the disease progresses.