Semantic Breakdown in Dementia: A Clue to Semantics in the Brain

Etsuro Mori　

Abstract:
The term semantic memory refers to the long-term storage of encyclopedic knowledge about the world (Tulving, 1972). Semantic memory is a separate subcategory of long-term memory containing the knowledge such as facts, words, objects, and their meaning, which is not attached to particular time and space contexts. It is involved in many cognitive processes such as recognizing objects, understanding the meaning of a spoken word, and converting from knowledge or concept into words for speaking. In speaking and comprehending language, semantic processing is fundamental as well as syntactic and phonological levels of processing. An approach to semantics is to study patients with dementia, where semantic breakdown is conceptually an essential component of dementia. Studies of semantic breakdown in dementia give important clues to the anatomical basis of semantic processing and to the concept of semantics. In this presentation, based on our recent studies on semantic breakdown in patients with dementia of various causes, including semantic dementia, Alzheimer's disease, and left anterior thalamic infarcts, I will elucidate the nature of semantic breakdown in patients with brain lesions and the anatomical basis of semantic processing.