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Speech connectedness discriminates Alzheimer’s Disease from cognitively healthy older adults and is associated with poorer semantic memory

Poster A45 in Poster Session A, Thursday, October 6, 10:15 am - 12:00 pm EDT, Millennium Hall

Bárbara L. C. Malcorra¹, Natália B. Mota^2,3, Janaina Weissheimer^4,5, Lucas P. Schilling¹, Maximiliano A. Wilson⁶, Lilian C. Hübner^1,5; ¹PUCRS, ²UFRJ, ³UFPE, ⁴UFRN, ⁵CNPq, ⁶Université Laval

Connected speech is commonly used over a lifespan in everyday conversation, representing an ecologically valid language production source. Narratives are a type of connected speech that require organizing a sequence of events in chronological order, with a well-established macro propositional organization, such as observing a plot with characters and a scenario. Difficulties with narrative production have been reported in clinical populations, including early-stage Alzheimer’s disease (AD). In addition, although deficits in semantic, episodic, and working memory seem to relate to connected speech difficulties, the contribution of each type of memory to connected speech is still not clear for AD. Taking this background into consideration, the aims of the present study are two-fold. First, to verify whether connected speech can differentiate oral narrative production between adults with AD and cognitively healthy older adults (HOA). Second, to verify whether specific speech graph attributes are associated with episodic, working, and semantic memory. Twenty-four AD patients (age=72.75±8.13; education=4.25±3.30) and forty-eight HOA (age=69.85±7.06; education=5.08±3.10) produced oral narratives based on a sequence of pictures, and performed episodic, working, and semantic memory tasks. Narratives were transcribed and each word was represented as a node and the temporal sequence was represented as directed edges. Since AD participants produced narratives with significantly smaller word counts than HOA, the narratives were analyzed using a moving window of a fixed word length (30 words) with a step of one word. Three connectedness attributes were calculated: 1) the number of edges, defined as each temporal connection between consecutive words; 2) the number of nodes in the largest connected component (LCC), defined as the largest set of nodes directly or indirectly linked by some path; and 3) the number of nodes in the largest strongly connected component (LSC), defined as the largest set of nodes directly or indirectly linked by reciprocal paths so that all the nodes in the component are mutually reachable. AD participants produced less connected narratives than the HOA, with fewer edges (p=0.0035) and smaller LSC (p=0.0116). Semantic memory correlated with LCC (Rho=0.59, p=0.002) exclusively in AD. Episodic memory correlated with LSC exclusively in HOA (Rho=0.47, p=<0.001). The results indicate that semantic memory deficits might lead to lower connected speech in AD, suggesting that such a link might represent a marker of AD, as it occurs exclusively under pathological conditions. These results suggest that the macrolinguistic deficits of patients with AD are linked primarily to deficits in cognitive processes in semantic memory rather than in episodic or working memory. Furthermore, while, in typical aging, the more verbal information or details one can access while planning a narrative, the more connected the graph representing that narrative is; in AD, semantic memory seems to take precedence over episodic memory to produce well-connected narratives . Overall, the results demonstrate the relevance of speech connectedness to discriminating between AD participants and HOA, representing a practical tool to assess cognitive impairment in AD patients.

Topic Areas: Language Production, Computational Approaches