Older adults have more language production difficulties than younger adults but display largely comparable language comprehension abilities. The Transmission Deficit Hypothesis suggests that production difficulties stem from an age-related increase in phonological signal transmission failures, while the semantic system, being more redundant than the phonological system, allows comprehension to be relatively preserved despite signal failures. Though the neural instantiation of the Transmission Deficit Hypothesis remains an open question, white matter represents one important factor to investigate. Metrics indicative of white matter connectivity across the brain, namely, Radial Diffusivity (RD) and Fractional Anisotropy (FA) have also been linked to age-related cognitive differences including naming difficulties. Using a Picture-Word Interference (PWI) task with 18 younger and 19 older healthy adults, we found that, across ages, better picture naming in the presence of phonological distractors was associated with lower RD across dorsal (r = −.35, p = .03), ventral (r = −.34, p = .04), and fronto-striatal (r = −.33, p = .04) tracts, and higher FA along dorsal tracts (r = .43, p = .008). The pattern of lower RD and higher FA, which is thought to reflect better white matter structure, points to the dorsal stream tracts as critical for performance on the PWI task. Moreover, the effects of RD and FA on performance were attenuated by the effect of age, reflecting the shared variance between age and white matter as it relates to language production ability.
As people age, one of the most common complaints is difficulty with word retrieval. A wealth of behavioral research confirms such age-related language production deficits, yet the structural neural differences that relate to age-related language production deficits remains an open area of exploration. Therefore, the present study used a large sample of healthy adults across adulthood to investigate how age-related white matter differences in three key left-hemisphere language tracts may contribute to age-related differences in language ability. Specifically, we used diffusion tensor imaging (DTI) to measure fractional anisotropy (FA) and radial diffusivity (RD) which are indicators of white matter structure. We then used a series of path models to test whether white matter from the superior longitudinal fasciculus (SLF), the inferior longitudinal fasciculus (ILF), and the frontal aslant tract (FAT) mediated age-related differences in one form of language production, picture naming. We found that FA, as well as RD from the SLF and FAT mediated the relation between age and picture naming performance, whereas a control tract (corticospinal; CST) was not a mediator. Moreover, differences between mediation of picture naming and a control naming condition suggest that left SLF has a greater role in higher-order aspects of naming, such as semantic and lexical selection whereas left FAT is more sensitive to sensorimotor aspects of fluency or speech motor planning. These results suggest that dorsal white matter contributes to age-related differences in generating speech and may be particularly important in supporting word retrieval across adulthood.
Aging is often associated with declines in language production. For example, compared to younger adults, older adults experience more tip-of-the-tongue (TOT) states, show decreased speed and accuracy in naming objects, and have more pauses and fillers in speech, all of which indicate age-related increases in retrieval difficulty. While prior work has suggested that retrieval difficulty may be phonologically based, it is unclear whether there are age-related differences in the organization of phonological information per se or whether age-related difficulties may arise from accessing that information. Here we used fMRI to investigate the neural and behavioral basis of phonological neighborhood denisty (PND) effects on picture naming across the lifespan (N=91, ages 20-75). Consistent with prior work, behavioral results revealed that higher PND led to faster picture naming times and higher accuracies overall, and that older adults were less accurate in their responses. Consistent with the behavioral analyses, fMRI analyses showed that increasing PND was associated with decreased activation in auditory and motor language regions, including bilateral superior temporal gyri and bilateral precentral gyri. Interestingly, although there were age-related increases in functional activation to picture naming, there were no age-related modulations of neural sensitivity to PND. Overall, these results suggest that having a large cohort of phonological neighbors facilitates language production, and although aging is associated with increases in language production difficulty, sensitivity to phonological features during language production is stable across the lifespan.
The purpose of the present study is to examine whether positive affect and negative affect can predict the changes in cognitive abilities, assessed by episodic memory and executive functioning, during the transition to late adulthood. Using the longitudinal data from the national survey of midlife development in the United States (MIDUS), this study implements a cross-lagged panel model to test the significance of two pathways; one from affect to cognition and the other in the opposite direction. The results show the three main findings: First, the relationship between affect and cognition is unidirectional in which only positive affect and negative affect during the first occasion significantly predict episodic memory in the second occasion. Second, regardless of the type of affect, higher levels of both positive and negative affect predicts worse episodic memory and this tendency is more prominent in older adults. The combined results emphasize the benefits of using affect as a predictor of changes in the specific types of cognition and suggest using the longitudinal model to account for complex relationships between these psychological constructs.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.