Generation, selection and sequencing in a case of Parkinson’s disease and primary progressive dynamic aphasia

Abstract

The rare language disorder of dynamic aphasia is reported in a case (MC) with the dual pathologies of non-fluent progressive aphasia and Parkinson’s disease. MC’s language profile was characterised by the hallmark propositional language impairment, as severe as other cases with dynamic aphasia, despite well-preserved core language skills (e.g., naming, reading, repetition, comprehension). Word and sentence generation performance was impaired only when many competing propositions were activated by a stimulus and not when a dominant proposition was available. Discourse generation was extremely reduced and perseverative, consistent with impaired generation and fluent sequencing of novel thoughts. In addition, non-verbal generation was impaired although dissociations emerged. MC was able to generate novel designs and gestures but his performance was highly perseverative. Motor movement selection was also abnormal, resembling a non-random pattern. MC is the first case of dynamic aphasia with concurrent deficits in three mechanisms thought crucial for conceptual preparation processes; namely impaired selection, impaired generation of novel thoughts and impaired fluent sequencing of novel thoughts. The implications are discussed in relation to conceptual preparation processes, accounts of dynamic aphasia and the supporting neural substrates for verbal and non-verbal generation.