ADYNAMIC APHASIA - A TRANSCORTICAL MOTOR APHASIA WITH DEFECTIVE SEMANTIC STRATEGY FORMATION

Adynamic aphasia is a form of transcortical motor aphasia characterize d by sparse but otherwise normal spontaneous speech that may improve w hen concepts are introduced by external stimuli. Akinesia, impaired co ncept formation, inertia of concept generation, a defective semantic n etwork, damage or impaired access to the verbal output lexicon, and de fective semantic strategy formation have been proposed to account for this disorder. We studied a patient with adynamic aphasia and frontal lobe systems dysfunction due to bilateral striatocapsular infarctions. The patient was not akinetic but did demonstrate inertia of concept g eneration that could be overcome with prompting. However, prompting di d not improve the number of concepts generated. He demonstrated a gene rally intact verbal lexicon and semantic network and normal lexical pr iming. However, his ability to sort closely related items into differe nt classes without prior cuing regarding the nature of the classes was defective. Although his verbal memory was normal, he appeared to use a serial rather than a semantic strategy to recall items. Finally, des pite normal lexical priming, he was impaired on a letter fluency task. These results most clearly demonstrate a defect in semantic strategy formation but indicate an additional and possibly related deficit in c oncept formation and a partial deficit in lexical strategy formation. All of these deficits appear to reflect impairment in the hierarchical organization of knowledge specific to the task at hand. This appears to be a key component of executive functions supported by frontal lobe systems.