14 The language disorder in semantic dementia: does it matter which language you speak?

Abstract

From its inception, Karalyn Patterson has shaped the field of cognitive neuropsychology - the study of how the brain’s structure and function relates to mental processes concerning the generation and use of knowledge. Specifically, Karalyn has used the effects of brain disease and injury to improve our understanding of language and memory. Her approaches are varied and rigorous, combining computer modelling and structural and functional brain imaging with observations of behaviour in normal and brain-damaged adults, as well as those affected by certain brain diseases. This has allowed Karalyn to directly link particular structures in the brain with specific cognitive issues. Karalyn’s research has important consequences for our understanding of brain conditions that affect memory; for example, Alzheimer’s disease and other forms of dementia. She has also revealed the impact of the same brain disorder on the speakers of two diverse languages, English and Japanese. Semantic dementia (SD) is a neurodegenerative condition in the spectrum of frontotemporal dementia, and considered to be one of the main varieties of primary progressive aphasia. The question in the title of this talk will be addressed from two different perspectives. The first asks whether the pattern of language features observed in SD varies in any principled and significant way across different languages. English and Japanese, for example, differ in almost every component of language – phonology, syntax, written form, etc; yet the profiles of language deficit in SD patients from these two language communities are virtually identical. From this perspective, therefore, the answer is no, it does not matter which language you speak. The second question asks whether the severity of the language disorder in SD varies in a principled and significant way across the two languages spoken by bilingual cases of SD. A high proportion of people living in India speak two or more languages. When bilingual Indian SD patients are given the same tests in their L1 and L2 languages, of course they are impaired in both, but they show a striking advantage for L1. Furthermore, and of substantial theoretical interest, the patients’ correct responses to test items in L2 are a virtually perfect subset of correct responses to the same test items in L1. From this perspective, therefore, the answer is yes, it does matter which language you are speaking. These contrasting answers to the two forms of the question follow from the following pair of hypotheses: (a) the language disorder in SD is a fairly pure reflection of a disintegrating semantic system, and (b) the semantic system is fundamentally language-independent. References Fushimi, T, Komori, K, Ikeda, M, Lambon Ralph, MA & Patterson, K. (2009). The association between semantic dementia and surface dyslexia in Japanese. Neuropsychologia. 2009;47:1061–1068. Patterson, K & Fushimi, T. Organisation of language in the brain: Does it matter which language you speak?Interdisciplinary Science Reviews2006;31:201–216 Ratnavalli, E, Narayana, J & Patterson, K(2019). Differential deterioration of languages in bilingual patients with semantic dementia: Implications for language representation in bilinguals. Under review.