Neural sensitivity to phonological characteristics is stable across the lifespan.

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.

Cerebral White Matter Mediation of Age-Related Differences in Picture Naming Across Adulthood.

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 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, 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) 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.

Neural sensitivity to semantic neighbors is stable across the adult lifespan.

As we age, language reflects patterns of both stability and change. On the one hand, vocabulary and semantic abilities are largely stable across the adult lifespan, yet lexical retrieval is often slower and less successful (i.e., slower picture naming times, increased tip of the tongue incidents). Although the behavioral bases of these effects have been well established, less is known about the brain regions that support these age-related differences. We used functional Magnetic Resonance Imaging (fMRI) to examine the neural basis of picture naming. Specifically, we were interested in whether older adults would be equally sensitive to semantic characteristics, specifically the number of semantic near neighbors. Near neighbors, defined here as items with a high degree of semantic feature overlap, were of interest as these are thought to elicit competition among potential candidates and increase naming difficulty. Consistent with prior reports, pictures with more semantic near neighbors were named more slowly and less accurately for all adults. Additionally, this interference for naming times was larger as age increased, starting around 30 years old. In contrast to the age-related behavioral slowing, the neural basis of these effects was stable across adulthood. Across all adults, a number of language-relevant regions including left posterior middle temporal gyrus and left inferior frontal gyrus, pars triangularis were sensitive to the number of near neighbors. Our results suggest that although middle-aged and older adults' picture naming is more slowed by increased semantic competition, the brain regions supporting semantic processes remain stable across the adult lifespan.

White matter disconnection is related to age-related phonological deficits.

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.

Sedentary Time is Associated with Worse Attention in Parkinson's Disease: A Pilot Study.

OBJECTIVE: Cognitive symptoms of Parkinson's disease (PD) may be alleviated by moderate-to-vigorous physical activity (MVPA), but no published research has characterized the relationship between objectively measured sedentary behavior and cognitive symptoms of PD. Therefore, the objective of this study was to assess the cross-sectional relationship between sedentary time and cognitive performance in a small pilot sample of individuals with mild-to-moderate PD. METHODS: Objective measures of sedentary time were obtained using an armband accelerometer. Cognition was assessed with the Parkinson's Disease Cognitive Rating Scale and a computerized task-switching paradigm. RESULTS: The percentage of awake time spent in sedentary activities was negatively correlated with attention (ß = -14.20, t(12) = -2.47, p = 0.03) but not other cognitive domains (p > 0.05) after controlling for MVPA and medication dosage. CONCLUSION: Sedentary activity may have unique associations with cognition, particularly attention, over and above MVPA in individuals with PD.