Trying to Put the Puzzle Together: Age and Performance Level Modulate the Neural Response to Increasing Task Load within Left Rostral Prefrontal Cortex

Abstract

Age-related working memory decline is associated with functional cerebral changes within prefrontal cortex (PFC). Kind and meaning of these changes are heavily discussed since they depend on performance level and task load. Hence, we investigated the effects of age, performance level, and load on spatial working memory retrieval-related brain activation in different subregions of the PFC. 19 younger (Y) and 21 older (O) adults who were further subdivided into high performers (HP) and low performers (LP) performed a modified version of the Corsi Block-Tapping test during fMRI. Brain data was analyzed by a 4 (groups: YHP, OHP, YLP, and OLP) × 3 (load levels: loads 4, 5, and 6) ANOVA. Results revealed significant group × load interaction effects within rostral dorsolateral and ventrolateral PFC. YHP showed a flexible neural upregulation with increasing load, whereas YLP reached a resource ceiling at a moderate load level. OHP showed a similar (though less intense) pattern as YHP and may have compensated age-effects at high task load. OLP showed neural inefficiency at low and no upregulation at higher load. Our findings highlight the relevance of age and performance level for load-dependent activation within rostral PFC. Results are discussed in the context of the compensation-related utilization of neural circuits hypothesis (CRUNCH) and functional PFC organization.

Reproducibility of Complex Functional Magnetic Resonance Imaging Effects

“…Most importantly, the results point toward a more‐efficient or ‘youth‐like’ load‐dependent up‐regulation of the spatial working memory network in older high‐performing subjects . Recent results confirmed these effects, although a different paradigm, a different design, and a different methodological approach were used (e.g., serial vs parallel stimulus presentation; retrieval vs recognition; load levels 4, 5, and 6 vs 1, 3, and 7; different region of interest masks and analysis of variance designs). Nevertheless, particularly for the left dorsolateral prefrontal cortex, activation patterns modulated by performance level and task load are surprisingly similar, which provides further evidence of the validity of these effects (compare left Figure 5A in with bottom Figure 4 in).…”

Load effects on spatial working memory performance are linked to distributed alpha and beta oscillations

“…Previous studies have implicated the ventrolateral PFC (VLPFC; including the IFG) in the selection, comparison, and judgment of task-relevant information (Glahn et al, 2002;Owen, McMillan, Laird, & Bullmore, 2005), and this region is further believed to support storage processes during WM performance (Bauer et al, 2015;Glahn et al, 2002;Owen, 2000;Owen et al, 1999;Wager & Smith, 2003). Previous studies have implicated the ventrolateral PFC (VLPFC; including the IFG) in the selection, comparison, and judgment of task-relevant information (Glahn et al, 2002;Owen, McMillan, Laird, & Bullmore, 2005), and this region is further believed to support storage processes during WM performance (Bauer et al, 2015;Glahn et al, 2002;Owen, 2000;Owen et al, 1999;Wager & Smith, 2003).…”

“…Additionally, using a delayed-recall spatial navigation task, Crespo-Garcia et al (2016) found that decreased theta activity within hippocampal, insular, and occipitotemporal regions during encoding was related to greater accuracy during recall. Concerning SWM load effects, there is some evidence that individuals who perform better on SWM tasks recruit left prefrontal regions more strongly as SWM load increases, relative to individuals who perform worse on such tasks (Bauer et al, 2015;Nagel et al, 2009). However, only one study has attempted to identify the oscillatory responses underlying such load-related behavioral differences.…”

Dissociating Normal Aging from Alzheimer’s Disease: A View from Cognitive Neuroscience

“…Another option to examine the impact of behavioral performance on brain activation is the comparison between high- and low-performing individuals in different age cohorts. An fMRI study of Bauer and colleagues, for example, revealed that older high-performers similar as younger high-performers showed increasing prefrontal activation with increasing working memory load [86]. This ‘youth-like’ pattern was less differentiated in older individuals but pointed toward an efficient recruitment of neural resources at increasing task demands.…”

“…Hypothetical model of left dorsolateral prefrontal cortex (DLPFC) activation modulated by age and performance level (particularly based upon the results of Nagel et al [69] and Bauer et al [86]). The bar chart indicates a flexible upregulation of DLPFC activation in YHP as neural response to increasing load.…”