Imaging studies of semantic memory

Abstract

The neural basis of semantic memory has not only theoretical interest, but also implications for several neurodegenerative disorders such as Alzheimer's disease and semantic dementia. The main focus of functional imaging studies is to disentangle the contribution of several interacting factors to the landscape of cerebral activation observed in normal individuals performing tasks requiring access to semantic knowledge (e.g. picture naming, word comprehension sentence verification). The main factors found to play a role are the modality of stimulus presentation (e.g. visual, verbal); the domain to which the stimuli belong (e.g. concrete or abstract entities; natural kinds or artifacts); and the type of knowledge accessed (e.g. visual properties vs. action properties). Another area of investigation is the neural correlates of semantic processes, such as selection among alternatives or information retrieval. The results of imaging studies confirm the neuropsychological concept that semantic knowledge and its usage depend upon a widely distributed network of brain areas. Specificity within this extended network, which includes a number of areas involved in perceptual and action processing, as well as the language areas, is related both to the type of knowledge and to different conceptual domains. The heterogeneous pattern of semantic memory dysfunction in neurological disorder may be a consequence of this complex neural organization.