Authors:

Thompson, S.A., GRAHAM, K.S., Williams, G., PATTERSON, K., Kapur, N. & HODGES, J.R

Reference:

Year of publication:

2002

CBU number:

5346

Abstract:

The cognitive architecture and neural underpinnings of person-specific semantic knowledge, and the degree too which this category dissociates from knowledge concerning objects and animals (general semantic knowledge), is highly controversial. The documentation of cases showing disruption of these categories in opposing directions would be particularly powerful evidence for separability, but to date no such double dissociation has been reported. To investigate this topic, tow patients with temporal lobe variant front-temporal dementia were administered two batteries of semantic tasks (one involving people and the other objects and animals) designed to assess input and output from both verbal and visual modalities. Tasks included confrontation naming, tests of conceptual knowledge, sorting and matching tasks. Performance was compared with 10 age and education-matched controls, MA and JP were found to show contrasting patterns of semantic impairment. MA demonstrated a cross modal loss of knowledge about objects and animals with only minor disruption to person-specific semantics; JP, in contrast, showed widespread damage to the semantic system underlying person knowledge but relative preservation of general knowledge. I n order to determine the neuroanatomical structures which might be specific to these two semantic domains, the technique of voxel-based morphometry was applied to MRI scans from each patient. Unilateral volume loss was found in the left infero-lateral temporal lobe in MA, and in the right temporal polar region in JP. These cases demonstrate that general and person-specific knowledge, are, in part, dissociable and may be differentially reliant upon the right (people knowledge) and left (general semantics) temporal lobes.