Load Modulation of BOLD Response and Connectivity Predicts Working Memory Performance in Younger and Older Adults

Abstract

■ Individual differences in working memory ( WM) performance have rarely been related to individual differences in the functional responsivity of the WM brain network. By neglecting person-to-person variation, comparisons of network activity between younger and older adults using functional imaging techniques often confound differences in activity with age trends in WM performance. Using functional magnetic resonance imaging, we investigated the relations among WM performance, neural activity in the WM network, and adult age using a parametric letter n-back task in 30 younger adults (21-31 years) and 30 older adults (60-71 years). Individual differences in the WM networkʼs responsivity to increasing task difficulty were related to WM performance, with a more responsive BOLD signal predicting greater WM proficiency. Furthermore, individuals with higher WM performance showed greater change in connectivity between left dorsolateral prefrontal cortex and left premotor cortex across load. We conclude that a more responsive WM network contributes to higher WM performance, regardless of adult age. Our results support the notion that individual differences in WM performance are important to consider when studying the WM network, particularly in age-comparative studies. ■

Inter-individual performance differences in younger and older adults differentially relate to amplitude modulations and phase stability of oscillations controlling working memory contents

“…In addition, non-phase locked activity reflecting the suppression of irrelevant information was also impaired in this group. Similar to other recent studies (Duverne et al, 2009;Nagel et al, 2009Nagel et al, , 2011Schneider-Garces et al, 2010), the present results underscore the heterogeneity of WM and episodic memory functioning among older adults, and are consistent with the proposition that older adults with more "youth-like" processing patterns tend to show higher levels of performance (e.g., Nagel et al, 2009). The present results are in line with a recently proposed conceptual framework for studying lifespan changes in episodic (Shing et al, 2008Werkle-Bergner et al, 2006) and working memory (Sander et al, 2011a(Sander et al, , 2011b, that dissociates the contributions of low-level feature binding and (strategic) control components to adult age differences in memory performance.…”

“…Nevertheless, speculative hints on the possible neuroanatomical difference may be derived from fMRI findings. In line with the present report, recent investigations of age-differences in fMRI activation patterns during WM-tasks demonstrate a dependence of the ability to modulate neuro-vascular responses on the individual performance level (e.g., Nagel et al, 2009Nagel et al, , 2011Schneider-Garces et al, 2010). In addition, Hedden et al (in press) could link a failure to modulate fMRI responses according to attentional demands in a subset of their older participants to elevated white matter hyperintensity (WMH) burden.…”

“…The increased heterogeneity of performance differences in groups of older adults has been mostly discussed on a theoretical level before , and had only recently be considered as an influential factor for understanding neural correlates of attentional and memory functions (e.g., Duverne et al, 2009;Hedden et al, in press;Nagel et al, 2009;Nagel et al, 2011). We added to this evidence by reporting specific performance-dependent differences in oscillatory correlates of WM processes.…”

Gender Differences in Visuospatial Working Memory —Does Emotion Matter?

“…This result matches the previous work on this topic (Cusack, Mitchell, & Duncan, 2010;Galy, Cariou & Mélan, 2011;Nagel et al, 2011;Tregellas, Davalos & Rojas, 2006), which has shown that these results are highly predictable from a neuro-cognitive perspective (see Schneider, 1999 for a review).…”

The cognitive neuroscience of ageing

“…Several recent studies have looked at specific functional connections during a task, and how these are affected by age. One study examined changes in brain activity during a working memory task with varying degrees of difficulty 87 and found that young adults had load-dependent increases of activity in PFC. Older adults showed relatively high levels of PFC activity across all load levels (consistent with CRUNCH, see above), and weaker functional connectivity between the premotor cortex and a left dorsolateral PFC region.…”