Selective dysfunction of tool-use: a failure to integrate somatosensation and action.

Apraxia is thought to reflect a disruption to high-level perceptual, cognitive and motor systems that form a distributed praxis network. Some authors suggest that apraxic deficits are unique to the neurology clinic; however, mounting evidence suggests that apraxic deficits are observable in natural contexts (e.g. Foundas et al., 1995). Naturalistic gesture production involves the integration of conceptual knowledge, gesture ideation, visual and somatosensory cues, and executive processes. Impairments in this context are therefore of interest from a clinical and theoretical standpoint. We present the case of a young female stroke patient (CK) demonstrating a novel limb praxis profile. CK's conceptual, evocation and praxis executive stages were evaluated: performance was contrasted to 30 healthy controls. CK was able to pantomime and imitate transitive gestures, suggesting that her ideational, executive and visual analytic systems were intact. Moreover, CK showed a good conceptual understanding of tools, objects and actions. However, CK demonstrated poor gesture production when actually using the tool associated with the action--a chronic and bilateral deficit that persisted at a 5-year follow-up assessment. Thus, CK's deficit appears to represent a specific and chronic disruption to high-level praxis systems that incorporates tactile inputs into the unfolding gesture production sequence.