Differential impairment of person-specific knowledge in a patient with semantic dementia

We report the case of ST, a 61-year-old gentleman of superior intelligence, who presented with a five-year history of slowly progressive word finding difficulty for proper names. MRI (magnetic resonance imaging) showed marked atrophy in the left anterior temporal lobe and SPECT (single photon emission computed tomography) demonstrated hypoperfusion in the left anterior and inferior temporal region. A detailed behavioral analysis of the integrity of his semantic system revealed naming deficits for both proper and common names. ST also showed severe impairments in person-specific semantic knowledge, but preservation of knowledge for famous places and common objects. ST's semantic knowledge deficit for people emerged whether he was tested with the faces or the names of famous individuals. Variables that affect name retrieval, such as familiarity, age of acquisition, and frequency of concept encounter, do not account for the selective impairment of person-specific knowledge evidenced by ST. Qualitative differences between the nature of knowledge representations for people and for common objects may underlie this effect. Disruptions in left temporal regions associated with semantic processing may be sufficient to produce a selective deficit in person-specific knowledge.