Conceptual Apraxia

Whereas patients with ideomotor apraxia make production errors (e.g., spatial and temporal errors), patients with conceptual apraxia make content and tool selection errors. These patients may not recall the type of actions associated with specific tools, utensils, or objects (tool-object action knowledge) and therefore make content errors.y , y For example, when asked to demonstrate the use of a screwdriver, either pantomiming or using the tool, the patient who has lost tool-object action knowledge may pantomime a hammering movement or use the screwdriver as if it were a hammer. Although this type of error may occur in the presence of an object agnosia, Ochipa and colleaguesy reported a patient who could name tools and therefore was not agnosic but often used them inappropriately.

Patients with conceptual apraxia may be unable to recall which specific tool is associated with a specific object ( tool-object association knowledge). For example, when shown a partially driven nail, they may select a screwdriver rather than a hammer from an array of tools. This conceptual defect may also be found in the verbal domain such that when an actual tool is shown to a patient, he or she may be able to name it (e.g., hammer), but when he is asked to name or point to a tool when its function is described, he cannot. These patients may also be unable to describe the functions of tools.

Patients with conceptual apraxia may also have impaired mechanical knowledge. For example, if they are attempting to drive a nail into a piece of wood and there is no hammer available, they may select a screwdriver rather than a wrench or pliers (which are hard, heavy, and good for pounding). y Mechanical knowledge is also important for tool development, and patients with conceptual apraxia may also be unable to correctly develop tools from available materials. Conceptual apraxia is perhaps most commonly seen in the degenerative dementia of the Alzheimer type, y but is also seen with hemispheric dysfunction. y

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