[Possible mechanism of body part as object and hand closing-in in apraxia]

We report a case of apraxia with pantomime where the patient exhibited body part as object (BPO) and hand closing-in errors as the symptoms of apraxia. The patient was a 52-year-old right-handed man who was clinically diagnosed with corticobasal degeneration. We tested the praxis ability of the patient by using 2 standard tests for apraxia: transitive gestures in response to verbal command and transitive gestures in response to visually presented objects. During the tests, the patient showed BPO errors and occasionally reached for the presented objects when he was instructed to pantomime their use without touching the objects (hand closing-in). Both BPO and hand closing-in were observed immediately after he was instructed to perform the target gestures. Hand closing-in was frequently observed when he was instructed to perform transitive gestures in response to visually presented objects. From the above results, we concluded that BPO is attributable to the inability to form precise finger postures for grasping objects, resulting in the "contamination" of the motor command by the information regarding the shape of the objects. Hand closing-in is considered to be caused by increased response to the presented object because of motor activation by perceived object images. On the whole, BPO and hand closing-in can be considered to be triggered by an overlap of objects with body images because of imprecise motor commands and increased responses to the object image.