JOINT COORDINATION DEFICITS IN LIMB APRAXIA

Competing models of the basis of limb apraxia were tested through anal ysis of joint coordination deficits in three apraxic subjects with les ions that included the left parietal lobe. Three-dimensional shoulder elbow, wrist and hand trajectories were recorded for repetitive 'slici ng' gestures made in a series of conditions in which contextual cues w ere introduced in a graded fashion. The apraxic subjects showed marked deficits in joint coordination across context conditions. Even when a ctually manipulating a tool and object, the apraxic subjects failed to show proper joint synchronization, failed to apportion their relative joint amplitudes properly, and failed to produce the correct phase re lationships among pairs of arm angles. Thus, apraxic subjects not only have deficits in the spatial plan for the movement, but they also hav e deficits in translating those plaits into the details of the angular motions at the joints, even when actually manipulating a tool and obj ect. These data support a model of apraxia in which apraxia can result from either the destruction of visuo-kinaesthetic motor representatio ns of learned movement, stored in posterior association cortex, or fro m a separation of these representations from premotor or motor areas.