Deregulated semantic cognition contributes to object‐use deficits in Alzheimer's disease: A comparison with semantic aphasia and semantic dementia

Abstract

Executive control is impaired from the early stages of Alzheimer's Disease (AD) and this produces deregulated semantic cognition (Corbett, Jefferies, Burns, & Lambon Ralph, ; Perry, Watson, & Hodges, ). While control deficits should affect semantic retrieval across all modalities, previous studies have typically focused on verbal semantic tasks. Even when non‐verbal semantic tasks have been used, these have typically employed simple picture‐matching tasks, which may be influenced by abnormalities in covert naming. Therefore, in the present study, we examined 10 patients with AD on a battery of object‐use tasks, in order to advance our understanding of the origins of non‐verbal semantic deficits in this population. The AD patients’ deficits were contrasted with previously published performance on the same tasks within two additional groups of patients, displaying either semantic degradation (semantic dementia) or deregulation of semantic retrieval (semantic aphasia; Corbett, Jefferies, Ehsan, & Lambon Ralph, ). While overall accuracy was comparable to the scores in both other groups, the AD patients’ object‐use impairment most closely resembled that observed in SA; they exhibited poorer performance on comprehension tasks that placed strong demands on executive control. A similar pattern was observed in the expressive domain: the AD and SA groups were relatively good at straightforward object use compared to executively demanding, mechanical puzzles. Error types also differed: while all patients omitted essential actions, the SA and AD groups’ demonstrations also featured unrelated intrusions. An association between AD patients’ object use and their scores on standard executive measures suggested that control deficits contributed to their non‐verbal semantic deficits. Moreover, in a task specifically designed to manipulate executive demand, patients with AD (and SA) exhibited difficulty in thinking flexibly about the non‐canonical uses of everyday objects, especially when distracted by semantically related objects. This study provides converging evidence for the notion that a failure of regulatory control contributes to multimodal semantic impairment in AD and uniquely demonstrates this pattern for the highly non‐verbal domain of object use.

The role of the right hemisphere in semantic control: A case-series comparison of right and left hemisphere stroke

“…We compared these trials (in the absence of cueing) to a second condition involving distractors that were related to the target word but that were weakly or unrelated to the probes (e.g., cat-attacks-paw → scrape-rub-scar- scratch ). SA patients have shown strong sensitivity to the strength of distracters in previous studies ( Corbett et al, 2014 , Noonan et al, 2010 ). Strong distracters create competition that patients with SA have difficulty resolving appropriately.…”

The contribution of executive control to semantic cognition: Convergent evidence from semantic aphasia and executive dysfunction

“…Eight SD patients tested in Manchester and Bath were available for the semantic distance task: GE, TM, JW, NH, JA, BS, ET, and PW. They have all been previously described (Corbett et al ., ; Hoffman, Evans, & Lambon Ralph, ; Hoffman, Jones, & Lambon Ralph, ; Hoffman & Lambon Ralph, ; Jefferies, Hoffman, et al ., ). All SD patients fulfilled published diagnostic criteria (Hodges et al ., ): They had word‐finding difficulties in the context of fluent speech and showed impaired semantic knowledge and single‐word comprehension: In contrast, phonology, syntax, visual–spatial abilities, and day‐to‐day memory were relatively well preserved.…”

“…An interaction between these components is envisaged within the controlled semantic cognition (CSC) framework (Jefferies, ; Lambon Ralph, Jefferies, Patterson, & Rogers, ; Rogers et al ., ). Patients with damage to these different components of semantic cognition show qualitatively different patterns of semantic impairment (Corbett, Jefferies, Burns, & Lambon Ralph, ; Corbett, Jefferies, Ehsan, & Lambon Ralph, ; Jefferies, Hoffman, Jones, & Lambon Ralph, ; Jefferies & Lambon Ralph, ; Jefferies, Patterson, & Lambon Ralph, ; Jefferies, Rogers, Hopper, & Lambon Ralph, ). However, the mechanisms underpinning semantic control are underspecified; in particular, it is unclear the extent to which this capacity draws on domain‐general executive control, and whether there are control processes specific to the semantic domain which allow the interaction of stored representations and current semantic contexts (Davey et al ., ; Noonan, Jefferies, Visser, & Lambon Ralph, ).…”

Auditory conflict and congruence in frontotemporal dementia

“…Consistent with previous work ( Krueger et al, 2009 , Seer et al, 2015 ), the present study does not support a clear dissociation of congruence judgment from other aspects of executive function, but rather suggests this may be an ecologically relevant marker of failing executive processes. Nonverbal executive deficits have been shown to develop during the evolution of SD as well as bvFTD ( Bozeat et al, 2000 , Corbett et al, 2015 , Gontkovsky, 2016 , Smits et al, 2015 ). In this regard, it is of interest that the bvFTD group (but not the SD group) also showed a deficit on the auditory perceptual control task, in keeping with a more fundamental impairment of change detection or monitoring in this syndrome.…”