The neural basis of semantic memory: evidence from semantic dementia

Semantic dementia (SD) is a syndrome of progressive impairment in semantic memory. Fifty-eight brain regions were measured in seven post mortem SD cases, ten normal controls and two disease controls (diagnosis frontotemporal dementia and motor neuron disease, FTD–MND). Manual segmentation of the whole brain has not previously been undertaken in a series of SD cases, either post mortem or during life. Widespread volume loss relative to controls was found in SD, with anterior temporal lobe regions bearing the brunt (>60% atrophy of temporopolar and perirhinal cortices bilaterally). Comparison of regional volumes in SD and FTD–MND found greater atrophy in SD only in temporopolar and perirhinal volumes. The sole region showing atrophy relative to controls in FTD–MND but not SD was motor cortex. Posterior temporal and frontal regions were not consistently affected and no significant asymmetry of atrophy was found. In summary, whole-brain regional evaluation in SD, in comparison with normal controls and FTD–MND, found anterior temporal atrophy encompassing the perirhinal cortex with relative sparing of adjacent posterior temporal regions.