Dynamic range of frontoparietal functional modulation is associated with working memory capacity limitations in older adults

Abstract

Older adults tend to over-activate regions throughout frontoparietal cortices and exhibit a reduced range of functional modulation during WM task performance compared to younger adults. While recent evidence suggests that reduced functional modulation is associated with poorer task performance, it remains unclear whether reduced range of modulation is indicative of general WM capacity-limitations. In the current study, we examined whether the range of functional modulation observed over multiple levels of WM task difficulty (N-Back) predicts in-scanner task performance and out-of-scanner psychometric estimates of WM capacity. Within our sample (60–77 years of age), age was negatively associated with frontoparietal modulation range. Individuals with greater modulation range exhibited more accurate N-Back performance. In addition, despite a lack of significant relationships between N-Back and complex span task performance, range of frontoparietal modulation during the N-Back significantly predicted domain-general estimates of WM capacity. Consistent with previous cross-sectional findings, older individuals with less modulation range exhibited greater activation at the lowest level of task difficulty but less activation at the highest levels of task difficulty. Our results are largely consistent with existing theories of neurocognitive aging (e.g. CRUNCH) but focus attention on dynamic range of functional modulation as a novel marker of WM capacity-limitations in older adults.

Default‐mode network dynamics are restricted during high speed discrimination in healthy aging: Associations with neurocognitive status and simulated driving behavior

“…These changes were characterized by a rise in activation in the aforementioned areas along with a diminished deactivation of the dorsal precuneus. All of these results are in consonance with the compensation hypothesis for the aging brain (Reuter‐Lorenz & Campbell, ; Reuter‐Lorenz & Park, ) which proposes that widespread hyperactivation from areas such as the cerebellum (Grady et al, ) or the frontoparietal cortex (Hakun & Johnson, ), along with DMN reduced deactivation, may act as a compensation measure, needed to reach youth‐like levels of task performance until it reaches a maximum and starts to decline. Usually, these changes in activation are in close relationship with changes in behavioral performance, which were also corroborated in this study.…”

Explaining age differences in working memory: The role of updating, inhibition, and shifting.

“…On a neural level, age-deficits in WM have been associated with an altered activation modulation in older adults: When processing a WM task, the activation of the fronto-parietal network would be broader and more rapid in older compared to younger adults (see e.g., Hakun & Johnson, 2017;Kaup, Drummond, & Eyler, 2014), which would lead to a less efficient activation of the regions that are specifically required for the particular WM task (also see Cappell, Gmeindl, & Reuter-Lorenz, 2010;Carp, Gmeindl, & Reuter-Lorenz, 2010;;Mattay et al, 2006;Nagel et al, 2011;Schneider-Garces et al, 2010). From a cognitive perspective, one important feature of WM is the system's limited capacity, which concurrently has to be shared between storage and online processing of information.…”

Contributions of white matter connectivity and BOLD modulation to cognitive aging: A lifespan structure-function association study

“…Both the ability to increase activity in regions showing positive modulation effects and the ability to decrease activity in regions showing negative modulation effects decreased as a function of age. Weakened positive and negative functional modulation to cognitive demand in healthy aging has been documented across various tasks (Persson et al 2007;Park 2010;Garrett et al 2013;Hakun and Johnson 2017;Kennedy et al 2017;Rieck et al 2017), and is thought to reflect age-related reductions in the ability to flexibly engage neural resources to meet task demands. Specifically, reductions in positive modulation with advancing age imply that aging limits the ability to upregulate task-relevant control regions to successfully perform a task, while reductions in negative modulation with age reflect less suppression of default processes under greater cognitive load in aging (Persson et al 2007;Sambataro et al 2010).…”

“…Studies utilizing lifespan samples demonstrate that aging affects the ability to both positively modulate (i.e., increase activity) and negatively modulate (i.e., deactivate) in response to parametrically increasing cognitive demands, and that age-related reductions in dynamic range of modulation are associated with poorer cognitive performance Rieck et al 2017). In these studies age-related decreases in positive modulation are typically evident in task-related fronto-parietal regions (Kennedy et al 2015Rieck et al 2017; see also Hakun and Johnson 2017, in an older adult sample), and are interpreted as reflecting reduced ability to successfully engage in strategic cognitive control processes under increasing task demands. These studies also demonstrate that aging is accompanied by decreased negative modulation to task difficulty (i.e., less deactivation with age) in regions typically associated with the default mode network (i.e., medial prefrontal cortex, anterior and posterior cingulate, precuneus, angular gyrus, and lateral temporal cortices; Persson et al 2007;Park et al 2010;Kennedy et al 2017;Rieck et al 2017), along with decreased functional connectivity among these regions (e.g., Sambataro et al 2010).…”

“…Dynamic range of blood-oxygen-level-dependent (BOLD) activity in response to parametrically increasing task demands decreases with age (Hakun and Johnson 2017;Kennedy et al 2017;Rieck et al 2017). Evidence from age comparison studies suggests that at low levels of task demands (or cognitive load) older adults increase their recruitment of cortical association regions in the prefrontal and parietal cortices, perhaps as a form of compensation to maintain similar levels of task performance as younger adults (Cappell et al 2010;Schneider-Garces et al 2010;Nagel et al 2011;Garrett et al 2013).…”