Category-specific semantic disorders in Alzheimer's disease.

A striking dissociation between the inability to identify living things plus food, along with a preserved ability to identify inanimate objects has been observed in patients who are recovering from herpes simplex encephalitis. In order to find out if a similar dissociation is also present in Alzheimer's disease (where the suspected initial site of parenchymal atrophy involves the same areas affected by herpes simplex virus), we carried out five experimental linguistic tasks to compare Alzheimer's patients' performance therein with that of vascular dementia patients and controls. Our results indicate a constant parallel between the category-specific semantic impairment of Alzheimer's patients and that described in patients recovering from herpes simplex encephalitis. The dissociation of living things+food vs inanimate objects in Alzheimer's disease appears to be of diagnostic value: it is not present in vascular dementia.