Category-specificity reflects not only the location but type of damage: Evidence from a direct comparison of HSVE, SD and an associated computational model of semantic memory

This talk will be based on a paper that will be published in Brain:
M.A. Lambon Ralph, C. Lowe, & T.T. Rogers (in press). Both type and distribution of damage are critical for category-specific semantic deficits: Evidence from semantic dementia, herpes simplex virus encephalitis and a neural network model of conceptual knowledge.
Abstract:
Studies of patients with semantic impairments following brain damage offer key insights into the cognitive and neural organisation of semantic memory. Especially important in this regard are studies of category-specific semantic impairment. We report a direct comparison of semantic deficits in two groups suffering from different diseases: semantic dementia (SD) and herpes simplex virus encephalitis (HSVE). Although pathology in both disorders is centred on the anterior temporal lobes bilaterally, category-specific semantic impairment is rarely observed in SD yet commonly found in HSVE. Using a combination of neuropsychology and computational neuroscience, we tested the possibility that category-specific deficits for living things depend not solely upon the location of damage within the cortical semantic network but also critically upon the type of impairment. When the semantic representations within the model are degraded or "dimmed" then a generalised, global semantic impairment results (as found in SD) but when the representations are distorted then a category-specific pattern emerges (as per HSVE). Three novel predictions from this model were tested and confirmed, thereby adding weight to the hypothesis that both type and distribution of pathology can be critical in producing neuropsychological phenomena.