Constrained principal component analysis reveals functionally connected load‐dependent networks involved in multiple stages of working memory

Abstract

Constrained principal component analysis (CPCA) with a finite impulse response (FIR) basis set was used to reveal functionally connected networks and their temporal progression over a multistage verbal working memory trial in which memory load was varied. Four components were extracted, and all showed statistically significant sensitivity to the memory load manipulation. Additionally, two of the four components sustained this peak activity, both for approximately 3 s (Components 1 and 4). The functional networks that showed sustained activity were characterized by increased activations in the dorsal anterior cingulate cortex, right dorsolateral prefrontal cortex, and left supramarginal gyrus, and decreased activations in the primary auditory cortex and "default network" regions. The functional networks that did not show sustained activity were instead dominated by increased activation in occipital cortex, dorsal anterior cingulate cortex, sensori-motor cortical regions, and superior parietal cortex. The response shapes suggest that although all four components appear to be invoked at encoding, the two sustained-peak components are likely to be additionally involved in the delay period. Our investigation provides a unique view of the contributions made by a network of brain regions over the course of a multiple-stage working memory trial.

Evidence for social working memory from a parametric functional MRI study

“…However, in contrast to previous nonsocial studies of working memory, we also observed load-dependent increases in mentalizing regions including dorsomedial prefrontal cortex (DMPFC) (−12, 38, 49) extending into anterior paracingulate cortex (DMPFC/APC) ( 12,29,31), precuneus/posterior cingulate cortex (PC/PCC) (0, −61, 46), and TPJ (−42, −70, 40) ( Fig. 2 and Table S2).…”

“…Our results indicate that at least some components of the mentalizing network are capacity limited and increase activity with effort and social load level. Such findings simultaneously inform and create possible hypotheses for research in social neuroscience, as well as research on the default-mode system, which previously characterized this network as interfering with, rather than supporting, effortful cognition (11,12).…”

“…Previous studies have uniformly found that increasing levels of cognitive load in working memory and other related tasks produces load-dependent decreases in the default-mode network that is essentially identical to the mentalizing network (10)(11)(12). Given past findings, it would have been reasonable to question whether previous mentalizing effects were partly artifacts of lower task difficulty compared with the nonsocial control tasks.…”

“…Finally, only mentalizing regions' parametric increases correlated with trait differences in perspective-taking ability. Prior meta-analyses of nonsocial working memory do not report mentalizing regions increasing with load (6); on the contrary, these regions are typically shown to reduce activation as a function of load in nonsocial working memory tasks (11,12).…”

“…Extant research suggests that the canonical working memory system supports effortful processing, whereas regions in the mentalizing system deactivate during effortful cognition, including during traditional working memory tasks (10,11). Essentially, the relationship between the canonical working memory network and the mentalizing network typically looks like two sides of a seesaw: as the lateral frontoparietal network parametrically increases in activation in response to cognitive effort or task demand, the mentalizing network shows parametric decreases (10)(11)(12). In fact, the mentalizing network is virtually identical to a network dubbed the "default-mode network" (13)(14)(15), so named because it is more active when individuals are at rest (i.e., by default) than when they engage in a variety of effortful cognitive tasks.…”