title: The degraded concept representation system in semantic dementia: damage to pan-modal hub, then visual spoke.
abstract: The core clinical feature of semantic dementia is a progressive yet selective degradation of conceptual knowledge. Understanding the cognitive and neuroanatomical basis for this deficit is a key challenge for both clinical and basic science. Some researchers attribute the deficit to damage to pan-modal conceptual representations that are independent of any particular sensory-motor modality and are represented in the ventrolateral anterior temporal lobes. Others claim that damage to modality-specific visual feature representations in the occipitotemporal 'ventral stream' is responsible. In the present study, we tested the hypothesis that concept degradation in semantic dementia involves a combination of these pan-modal and modality-specific elements. We investigated factors influencing knowledge of object concepts by analysing 43 sets of picture-naming data from patients with semantic dementia. We found a strong influence of two pan-modal factors: highly familiar and typical items were named more accurately than less familiar/atypical items at all stages of the disorder. Items associated with rich sensory-motor information were also named more successfully at all stages, and this effect was present for sound/motion knowledge and tactile/action knowledge when these modalities were studied separately. However, there was no advantage for items rich in visual colour/form characteristics; instead, this factor had an increasingly negative impact in the later stages of the disorder. We propose that these results are best explained by a combination of (i) degradation of modality-independent conceptual representations, which is present throughout the disorder and is a consequence of atrophy focused on the ventrolateral anterior temporal lobes; and (ii) a later additional deficit for concepts that depend heavily on visual colour/form information, caused by the spreading of atrophy to posterior ventral temporal regions specialized for representing this information. This explanation is consistent with a graded hub-and-spoke model of conceptual knowledge, in which there is a gradual convergence of information along the temporal lobes, with visual attributes represented in the posterior cortex giving way to pan-modal representations in the anterior areas.
authors.affiliation: Neuroscience and Aphasia Research Unit (NARU), Zochonis Building, School of Psychological Sciences, University of Manchester, Oxford Road, Manchester, M13 9PL, UK. paul.hoffman@manchester.ac.uk
authors.forename: Paul
authors.initials: P
authors.lastname: Hoffman
authors.forename: Roy W
authors.initials: RW
authors.lastname: Jones
authors.forename: Matthew A Lambon
authors.initials: MA
authors.lastname: Ralph
mesh_terms: D000161:Acoustic Stimulation; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003072:Cognition Disorders / Q000175:diagnosis / Q000209:etiology*; D003210:Concept Formation / Q000502:physiology*; D005260:Female; D057174:Frontotemporal Lobar Degeneration / Q000150:complications*; D006801:Humans; D008297:Male; D008875:Middle Aged; D008960:Models, Psychological; D009275:Names; D009483:Neuropsychological Tests; D010775:Photic Stimulation; D021641:Recognition, Psychology / Q000502:physiology; D012189:Retrospective Studies; D012677:Sensation / Q000502:physiology*; D014110:Touch / Q000502:physiology; D014705:Verbal Behavior / Q000502:physiology*; D014796:Visual Perception / Q000502:physiology