Context-specific differences in fronto-parieto-occipital effective connectivity during short-term memory maintenance

Abstract

Although visual short-term memory (VSTM) performance has been hypothesized to rely on two distinct mechanisms, capacity and filtering, the two have not been dissociated using network-level causality measures. Here, we hypothesized that behavioral tasks challenging capacity or distraction filtering would both engage a common network of areas, namely dorsolateral prefrontal cortex (dlPFC), superior parietal lobule (SPL), and occipital cortex, but would do so according to dissociable patterns of effective connectivity. We tested this by estimating directed connectivity between areas using conditional Granger causality (cGC). Consistent with our prediction, the results indicated that increasing mnemonic load (capacity) increased the top-down drive from dlPFC to SPL, and cGC in the alpha (8−14 Hz) frequency range was a predominant component of this effect. The presence of distraction during encoding (filtering), in contrast, was associated with increased top-down drive from dlPFC to occipital cortices directly and from SPL to occipital cortices directly, in both cases in the beta (15−25Hz) range. Thus, although a common anatomical network may serve VSTM in different contexts, it does so via specific functions that are carried out within distinct, dynamically configured frequency channels.

Identification of Two Distinct Working Memory-Related Brain Networks in Healthy Young Adults

“…Our findings of a frontally-centered and a parietally-centered network involved in different aspects of WM-task performances are in line with recent ROI-based studies that have reported distinct functional roles of frontal and parietal regions on WM ( Kundu et al, 2015 ; Sarma et al, 2016 ; Li et al, 2017 ). The functional results from our estimated networks were also consistent with the voxel-wise results from our data.…”

“…Stimulating the right parietal cortex increased the amount of information maintained in the visual WM, whereas stimulating the right PFC improved focusing on relevant information and directing attention away from irrelevant stimuli ( Li et al, 2017 ). In addition, measuring the directed connectivity between the DLPFC and superior parietal lobule (SPL) during a visual WM task hinted toward a top-down drive from DLPFC to SPL that increased with WM load ( Kundu et al, 2015 ). These insights were based on a priori defined regions of interest (ROIs) and therefore described functional properties of separate brain regions.…”

Theta and Alpha Oscillations during the Retention Period of Working Memory by rTMS Stimulating the Parietal Lobe

“…Several recent studies have reported connections between these two cortices. Kundu et al ( 2015 ) found increased directed connectivity between the prefrontal and parietal areas during the “retention” process by using the Granger causality of the alpha oscillation; however, similar results were also observed between both the prefrontal and occipital areas, and the parietal and occipital areas during the “coding” process. In addition, Harding et al ( 2015 ) established a brain network model for cognitive control and WM, which included the inferior frontal junction, dorsolateral prefrontal cortex (DLPFC), pre-supplementary motor area, and intra-parietal sulcus, and analyzed the causality between different cortical regions via functional magnetic resonant imaging (fMRI).…”

Comparing the Effects of 10-Hz Repetitive TMS on Tasks of Visual STM and Attention

“…Moreover, although the iIPS may play a role in both tasks, successfully performing the two tasks may require this region to exert its effects on other brain regions in different ways. For example, whereas activity in the alpha-band range may be linked to the role of spatial attention (e.g., Grimault et al, 2009), inhibition (e.g., Jensen & Mazaheri, 2010), or binding (Johnson et al, 2011) in VSTM, successfully perceiving an event may depend on long-range synchronization in the alpha and/or beta band between posterior parietal cortex and frontal and/or extrastriate regions (Kundu, Chang, Postle, & Van Veen, 2015; Gross et al, 2004). …”