Non-verbal semantic impairment in stroke aphasia: A comparison with semantic dementia

Introduction: Semantic dementia (SD) is a neurodegenerative disease, associated with focal atrophy of the anterior temporal lobes bilaterally. SD produces a specific and progressive impairment of semantic memory that affects comprehension in all modalities (Bozeat et al., 2000; Snowden et al., 1989). This suggests anterior temporal cortex is the repository of multimodal semantic knowledge (Rogers et al., 2004). In contrast, comprehension-impaired CVA patients have infarction of very different brain regions: typically temporoparietal or frontotemporal cortex in the left hemisphere only (Berthier, 2001; Chertkow et al., 1997). The anterior temporal lobes, which receive two arterial supplies, are highly unlikely to be damaged bilaterally after stroke. This apparent inconsistency between SD and stroke aphasia raises several important questions: (1) can stroke aphasics show deficits on non-verbal as well as verbal semantic tasks (limited evidence suggests that they can (Chertkow et al., 1997; Hart & Gordon, 1990) and (2) if so, is the nature of the comprehension impairment the same in the two conditions? We present the first (to our knowledge) case-series comparison of SD and comprehension-impaired stroke aphasics to address these issues.