Pantomime versus actual tool use: alterations of movement kinematics with the mode of execution and with brain damage

Abstract

Apraxic stroke patients demonstrate impaired miming of the use of common tools. A subset of these patients may show a deficit in the actual use of these tools as well. As movement goals and task mechanics differ substantially between actual tool use and corresponding pantomimes, we aimed to understand whether this interpersonal variability in apraxia is due to a general deficit affecting both modes of action execution or whether some patients show an association of two distinct functional impairments. In the present study, we assessed repetitive ladle scooping movements in brain damaged patients with and without apraxia using their ipsilesional hand and healthy control subjects and compared their movement kinematics between three execution modes: pantomime, demonstration with the tool only, and actual use in the normal context. Analysis of the wrist trajectory during the ladle transport revealed clear differences between the execution modes, such as slower actual use, and moderate deficits in patients with left brain damage (LBD). LBD patients were impaired in the scooping component: especially, LBD patients with apraxia yielded reduced hand rotation at the bowl and the plate. This deficit was most obvious during pantomime but actual use was also affected and reduced hand rotation was consistent across conditions as indicated by pair-wise correlations between the execution modes. In contrast in healthy control subjects, correlations of movement parameters were most evident between the pantomime and demonstration modes but weak in pairs including actual use. We conclude from our findings that for a specific tool use action, common motor schemas are activated but are adjusted according to the constraints of the task and its demands. Therefore, an apraxic LBD individual can show a common deficit across all action conditions but the severity of which can differ substantially.