A body part as object (BPO) gesture is one of the error patterns in apraxia. In the BPO gesture, people represent objects by their hands. To clarify the neuronal background of the BPO gesture, we compared the brain activation during the BPO gesture with that during ordinary pantomime in normal subjects using functional magnetic resonance imaging. Both the BPO gesture and the pantomime induced activation in the left parietal areas (Brodmann's area (BA) 7, 40), irrespective of the hand used. These areas might be activated by a common process of tool-related gestures. The BPO gesture also activated the right supramarginal gyrus (BA 40). This activation might reflect the characteristic process of BPO, the correlation of hands with tools by their forms and movements.

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The neuronal system to process and transfer auditory information to the higher motor areas was investigated using fMRI. Two different types of internal modulation of auditory pacing (1 Hz) were combined to design a 2x2 condition experiment, and the activation was compared with that under a visual guidance. The bilateral anterior portion of the BA22 (ant-BA22) and the left BA41/42 were more extensively activated by the combined modulation condition under the auditory cue than that under the visual cue. Among the four auditory conditions with or without the two types of internal modulation, the activation in the ant-BA22 was augmented only on the left side by the combined modulation condition. The left ant-BA22 may be especially involved in integrating the external auditory cue with internal modulation, while the activation on the right side did not depend on the complexity. The role of the left BA41/42 in motor regulation may be more specific to the processing of an auditory cue than that on the right side. These two areas in the left temporal lobe may be organized as a subsystem to handle the timing of complex movements under auditory cues, while the higher motor areas in the frontal lobe support both sensory modalities for the cue. This architecture may be considered as 'audio-motor control', which is similar to the visuo-motor control of the front-parietal network.

No abstract