Neural changes associated with semantic processing in healthy aging despite intact behavioral performance

Abstract

Semantic memory recruits an extensive neural network including the left inferior prefrontal cortex (IPC) and the left temporoparietal region, which are involved in semantic control processes, as well as the anterior temporal lobe region (ATL) which is considered to be involved in processing semantic information at a central level. However, little is known about the underlying neuronal integrity of the semantic network in normal aging. Young and older healthy adults carried out a semantic judgment task while their cortical activity was recorded using magnetoencephalography (MEG). Despite equivalent behavioral performance, young adults activated the left IPC to a greater extent than older adults, while the latter group recruited the temporoparietal region bilaterally and the left ATL to a greater extent than younger adults. Results indicate that significant neuronal changes occur in normal aging, mainly in regions underlying semantic control processes, despite an apparent stability in performance at the behavioral level.

Aging Modulates the Hemispheric Specialization during Word Production

“…We observed that L AP asymmetry was higher for older participants than younger ones, suggesting the use of a semantic strategy to perform naming with aging. Our findings are in line with Ansado et al (2013) and Lacombe et al (2015), as these authors suggest that older participants rely on preserved semantic mechanisms by over-recruiting left temporo-parietal regions to perform the task. We posit that this result, referred as the left anterior-posterior aging effect (LAPA), reflects a domain-specific (linguistic) strategy to maintain performance in older adults for tasks involving semantic processes.…”

“…In line with the semantic hypothesis, using functional magnetic resonance imaging (fMRI), Baciu et al (2016) reported higher supplementary bilateral posterior temporo-parietal activity for object naming in older adults compared to younger adults, suggesting greater involvement of lexico-semantic processes. This is in agreement with findings from Ansado et al (2013) for lexical production, and Lacombe et al (2015) for language comprehension. In addition, Lacombe et al (2015) reported that increased posterior activity observed in older adults reflects age-related reorganization of networks responsible for the conceptual retrieval and semantic representations of words.…”

“…This is in agreement with findings from Ansado et al (2013) for lexical production, and Lacombe et al (2015) for language comprehension. In addition, Lacombe et al (2015) reported that increased posterior activity observed in older adults reflects age-related reorganization of networks responsible for the conceptual retrieval and semantic representations of words. Ansado et al (2013) suggested that preserved lexical production in older adults could be explained by greater support from semantic processes in temporal regions (Verhaeghen, 2003; Patterson et al, 2007).…”

“…Based on previous studies, we initially hypothesized that two strategies could be developed by older adults to perform lexical production: a semantic strategy suggesting supplementary involvement of semantic processes (Ansado et al, 2013; Lacombe et al, 2015) and/or an executive strategy assuming that in case of difficulty in performing the task, older adults would recruit executive functions to retrieve and generate words faster (Wierenga et al, 2008). We observed that L AP asymmetry was higher for older participants than younger ones, suggesting the use of a semantic strategy to perform naming with aging.…”

Diagnostic and Prognostic Role of Semantic Processing in Preclinical Alzheimer’s Disease

“…These two converging pieces of evidence would suggest that, if anything, ageing should result in a prominent lexical-semantic decline. Instead, only a moderate decrease is detected, and there are studies showing either no effects [40], or even improvement with age [41]. In part, this counterintuitive observation could be due to neural compensation that is present in wellfunctioning older people.…”