Neural mechanisms of articulatory motor speech deficit in post-stroke aphasia: An ERP study

Auditory-motor integration is crucial for speech production, yet its underlying neural mechanisms remain poorly understood in individuals with aphasia following left-hemisphere stroke. This study utilized event-related potentials (ERPs) to investigate the neural correlates of speech production and auditory feedback control under a formant alteration paradigm in aphasia. A total of 20 participants with post-stroke aphasia and 22 controls performed a monosyllabic word production task under randomized normal (i.e. no shift) and altered auditory feedback (AAF) trials by applying a +30 % upward shift to the first formant (F1) frequency during concurrent electroencephalography (EEG) recordings. The analysis of pre-speech ERPs (readiness potentials) did not reveal any neural activity differences between and within groups. However, we found that the aphasia group exhibited significantly smaller ERP amplitudes compared with controls irrespective of auditory feedback condition following the onset of speech production. In addition, post-speech ERPs were significantly larger in the anterior vs. posterior regions in controls, but no such difference was present in the aphasia group. Moreover, no laterality effect was observed, suggesting a bilateral distribution of neural activities in both groups. Finally, the AAF did not elicit any between-group ERP differences, and this effect was consistent with behavioral compensatory responses to formant alterations. These findings highlight reduced articulatory neural responsiveness in aphasia, particularly in the anterior cortical regions implicated in speech production and motor control. The absence of the AAF effect suggests limited sensitivity to feedback alterations in both groups, potentially due to motor adaptation of the underlying mechanisms over repeated formant-shifting trials.