Our ability to use objects and tools to perform actions is essential to our daily activities, and it is developed to a level that is unique to our species.
In a study performed by a scientific team of the French National Center for Scientific Research (CNRS) and the Paris Descartes University, published by Elsevier in the April 2009 issue of Cortex (www.elsevier.com/locate/cortex), researchers have found that brain-lesioned patients who have difficulties using familiar objects and tools in their usual context (e.g. cutting paper with scissors) may also be impaired at controlling the movement of an object in the context of simpler movements such as pointing at a target.
Patients suffering from apraxia, a neurological syndrome caused by lesions in the left hemisphere of the brain, have difficulties executing complex movements, including tool use gestures. In this study, the authors compared the performance of apraxics to that of other patients suffering from left cerebral lesion but showing no sign of apraxia, on a task requiring them to point at targets with a stick. Apraxics performed significantly worse than control patients, committing larger errors and sometimes failing to anticipate the changes in movement coordination imposed by the use of a long object to point at a target within hand reach.
Apraxia is often thought to be due to a loss in the ability to translate memories of well-learned gestures into a specific sequence of movements. With these new findings, the authors suggest that some of those patients are also impaired in more elementary processes that allow the incorporation of an object as a functional extension of their limb into their body coordination.