Selective impairment of transitive gestures: An unusual case of apraxia

We describe the case of a 74-year-old man with selective apraxia for transitive gestures (gestures of object use) following a left temporo-parietal infarction. We document his neuropsychological progress over 2 years and assess his praxic abilities according to the best-developed cognitive model of praxis. Strikingly, PF was unable to pantomime transitive gestures in every test modality (verbal command, imitation, photographs of objects and handling actual tools), but could still execute symbolic (e.g. salute) and meaningless gestures. He was able to discriminate and recognize transitive gestures as well as controls. His praxic impairment has persisted through the years in the absence of dementia. His inability to use tools cannot be accounted for on the basis of a visual agnosia, impaired language comprehension or a classic ideomotor apraxia. Such a selective deficit of transitive gestures is incompatible with the cognitive model proposing that the production of all meaningful gestures (symbolic and transitive) requires a final common pathway. Rather, these findings indicate a selective deficit in the production system, which is inefficient at implementing specific representations for complex object-related gestures. Our findings also support a dissociation between semantic (what) and functional (how) knowledge of an object.