Neural basis of pantomiming the use of visually presented objects.

UNLABELLED: Neuropsychological studies of patients suffering from apraxia strongly imply a left hemisphere basis for skillful object use, the neural mechanisms of which, however, remain to be elucidated. We therefore carried out a PET study in 14 healthy human volunteers with the aim to isolate the neural mechanisms underlying the sensorimotor transformation of object-triggers into skilled actions. We employed a factorial design with two factors ( RESPONSE: naming, pantomiming; and TRIGGER: actions, objects) and four conditions (IA: imitating the observed pantomime; IO: pantomiming the use of the object shown; NA: naming the observed pantomime; NO: naming the object shown). The design thus mainly aims at investigating the interaction [i.e. (IO-IA)-(NO-NA)] which allows the assessment of increased neural activity specific to the sensorimotor transformation of object-triggers into skilled actions. The results (P < 0.05, corrected) showed that producing a wide range of skilled actions triggered by objects (controlled for perceptual, motor, semantic, and lexical effects) activated left inferior parietal cortex. The data provide an explanation for why patients with lesions including left parietal cortex suffer from ideational apraxia as assessed by impaired object use and pantomining to visually presented objects.