Neuropsychological studies of patients suffering from apraxia strongly
imply a left hemisphere basis for skilful object use, the neural
mechanisms of which, however, remain to be elucidated. We therefore
carried out a PETstudy 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 pontomining
to visually presented objects (Brain 111 (1988) 1173; Cogn. Neuropsychol.
18 (2001) 671).
