Category-specific form-knowledge deficit in a patient with herpes simplex virus encephalitis.

In-depth case study of a herpes simplex virus encephalitis patient who presents with a relatively clear knowledge disorder and anterograde amnesia in the absence of any other major cognitive deficit. The main neuropsychological feature is a category-specific impairment restricted to living things. The patient misnamed pictures of animals and vegetables, could not accurately draw animals from memory or verbally describe their visual appearance, and was not accurate in sorting pictures of real animals from pictures of unreal animals; conversely, in the same tasks her performance with artifactual objects was either errorless or superior to that with animals. We interpret the patient's category-specific deficit as due to a selective disturbance within the structural description system, rather than a deficit in low-level visual processing or semantic memory. From this case study and a review of other reported cases we claim that such deficit of form-knowledge is a consequence of the extensive lesions that affect bilaterally the inferior parts of the temporal lobes. The patient here described thus offers further empirical evidence for the crucial role of the inferotemporal cortex in processing visual knowledge about concepts.