[Cognitive neuropsychological investigation of apraxia]

Apraxia is a higher-order motor disturbance of goal-directed behavior characterized by an inability to perform skilled, previously learned movements in the absence of weakness and sensory defects. Clinical findings associated apraxia are divided into two large domains, production and conceptual. In this study, we reports two severely apraxic patients, case TT and UH, whose performances suggests that production and conceptual domains may be dissociable. Case TT is a 67-year-old, right-handed man who showed content errors on actual tool use, gesture production to command and gesture to sight of tool after a left inferior parietal infarction. He demonstrated severely impaired conceptual knowledge on tool-action and tool-object associative tests with intact recognition of many common tools. On the other hand, case UH, who is 79-year-old, mixed-handed man, had spatial and movement errors on gesture production to command and gesture to sight following a right fronto-parietal infarction. His performances on tests of conceptual praxis knowledge were intact. Gesture recognition was preserved in both cases. The selective impairment of conceptual praxis knowledge and action production in two cases supports the notion that production and conceptual systems are distinct features of the representation of object-oriented action.