Neural and Behavioral Predictors of Speech Motor Sequence Learning in Primary Progressive Aphasia

This study investigated the clinical and neural correlates of speech motor sequence learning in primary progressive aphasia (PPA) to test specific predictions regarding the roles of the left posterior inferior frontal sulcus (pIFS) and left ventral premotor cortex (vPMC). A cohort of 26 participants with PPA completed a 2-day non-native consonant cluster learning paradigm. Participants also completed a battery of clinical speech-language assessments, including tests of phonological and motor programming ability, and T1-weighted structural MRI scans were obtained for a subcohort (n = 19) of participants. Mean cortical thickness measures were extracted using FreeSurfer software for each cortical region of interest. Separate statistical analyses were conducted to test for correlations between learning outcomes on the consonant cluster paradigm (both error rate and duration) with (1) clinical measures and (2) cortical thickness. Both analyses indicated a dissociation between correlates of error rate and duration: Duration was more strongly associated with sensorimotor cortex (including the left vPMC) and clinical motor speech measures, while error rate was primarily associated with phonological working memory correlates (including the left pIFS) and clinical repetition measures.