Neural Correlates of Naturally Occurring Speech Errors during Picture Naming in Healthy Participants.

Most of our knowledge about the neuroanatomy of speech errors comes from lesion-symptom mapping studies in people with aphasia and laboratory paradigms designed to elicit primarily phonological errors in healthy adults, with comparatively little evidence from naturally occurring speech errors. In this study, we analyzed perfusion fMRI data from 24 healthy participants during a picture naming task, classifying their responses into correct and different speech error types (e.g., semantic, phonological, omission errors). Total speech errors engaged a wide set of left-lateralized frontal, parietal, and temporal regions that were almost identical to those involved during the production of correct responses. We observed significant perfusion signal decreases in the left posterior middle temporal gyrus and inferior parietal lobule (angular gyrus) for semantic errors compared to correct trials matched on various psycholinguistic variables. In addition, the left dorsal caudate nucleus showed a significant perfusion signal decrease for omission (i.e., anomic) errors compared with matched correct trials. Surprisingly, we did not observe any significant perfusion signal changes in brain regions proposed to be associated with monitoring mechanisms during speech production (e.g., ACC, superior temporal gyrus). Overall, our findings provide evidence for distinct neural correlates of semantic and omission error types, with anomic speech errors likely resulting from failures to initiate articulatory-motor processes rather than semantic knowledge impairments as often reported for people with aphasia.