[Anatomical and functional specialization of the cortex and the organization of gestures. An animal experimental contribution to the study of apraxia].

Apraxia has traditionally been considered the province of clinical investigation, but in recent years a series of animal studies have provided data that appear to be relevant to its interpretation. They are reviewed in the present paper with the aim to integrate and specify the classical model proposed by Liepmann, particularly as far as the roles of the inferior parietal lobe (area 40 in man and part of area 7 in the monkey) and of the motor association cortex (area 6 in man and periarcuate area in the monkey) are concerned. Monkey data suggest that the relation of the inferior parietal lobe to apraxia is not simply due to the interruption of the many sensory pathways that run in the subjacent white matter towards the frontal lobe, as implied by Liepmann's theorization, but rather to its being a center specialized in planning motor programs. Specifically, it would award the gesture with the spatial (directional) features needed to its proper execution. The periarcuate area, on the other hand, would participate in the organization of gesture, programming the temporal sequence of its component movements. It is in a favourable position to do this, because this receives information not only from the sensory association areas and the inferior parietal lobe, but also from the cortex of the depth and around the sulcus principalis, which is committed to keep record of the spatial characteristics of the stimulus as well as of the motor response. The implications of this dual system for the interpretation of apraxia in man are discussed.