Visual Short-Term Memory Activity in Parietal Lobe Reflects Cognitive Processes beyond Attentional Selection

Abstract

Visual short-term memory (VSTM) and attention are distinct yet interrelated processes. While both require selection of information across the visual field, memory additionally requires the maintenance of information across time and distraction. VSTM recruits areas within human (male and female) dorsal and ventral parietal cortex that are also implicated in spatial selection; therefore, it is important to determine whether overlapping activation might reflect shared attentional demands. Here, identical stimuli and controlled sustained attention across both tasks were used to ask whether fMRI signal amplitude, functional connectivity, and contralateral visual field bias reflect memory-specific task demands. While attention and VSTM activated similar cortical areas, BOLD amplitude and functional connectivity in parietal cortex differentiated the two tasks. Relative to attention, VSTM increased BOLD amplitude in dorsal parietal cortex and decreased BOLD amplitude in the angular gyrus. Additionally, the tasks differentially modulated parietal functional connectivity. Contrasting VSTM and attention, intraparietal sulcus (IPS) 1-2 were more strongly connected with anterior frontoparietal areas and more weakly connected with posterior regions. This divergence between tasks demonstrates that parietal activation reflects memory-specific functions and consequently modulates functional connectivity across the cortex. In contrast, both tasks demonstrated hemispheric asymmetries for spatial processing, exhibiting a stronger contralateral visual field bias in the left versus the right hemisphere across tasks, suggesting that asymmetries are characteristic of a shared selection process in IPS. These results demonstrate that parietal activity and patterns of functional connectivity distinguish VSTM from more general attention processes, establishing a central role of the parietal cortex in maintaining visual information. Visual short-term memory (VSTM) and attention are distinct yet interrelated processes. Cognitive mechanisms and neural activity underlying these tasks show a large degree of overlap. To examine whether activity within the posterior parietal cortex (PPC) reflects object maintenance across distraction or sustained attention per se, it is necessary to control for attentional demands inherent in VSTM tasks. We demonstrate that activity in PPC reflects VSTM demands even after controlling for attention; remembering items across distraction modulates relationships between parietal and other areas differently than during periods of sustained attention. Our study fills a gap in the literature by directly comparing and controlling for overlap between visual attention and VSTM tasks.

Dissecting the neural focus of attention reveals distinct processes for spatial attention and object-based storage in visual working memory

“…However, in this study, we extend the growing evidence that the focus of attention may be implemented via multiple component processes playing distinct functional roles: one that represents currently prioritized space (alpha); and another that reflects item storage within the focus of attention (CDA). This proposal converges with other findings that suggest a dissociation between spatial attention and WM storage (Tas et al, 2016;Sheremata et al 2018). van Dijk et al (2010) proposed that asymmetric modulations of alpha power at the trial-level can generate a CDA-like negative slow wave in an event-related average.…”

“…Our interpretation of the CDA as an index of continued representations of object files critically hinges on a distinction between the maintenance of items in working memory and the maintenance of spatial information without an accompanying item representation. While some may view this as provocative, recent work has shown dissociable patterns of activity in parietal lobe between WM and spatial attention demands (Sheremata, Somers, & Shomstein, 2018). Additionally, we note that there is a longstanding precedent for a distinction between the representation of an object and the representation of the features or identifying labels associated with that object.…”

Multi‐target attention and visual short‐term memory capacity are closely linked in the intraparietal sulcus

“…;Sheremata & Silver, 2015;Sheremata, Somers, & Shomstein, 2018). Thus, by targeting these more posterior areas of the IPS, it is possible that these previous TMS studies were capable of eliciting extinction-like behavior by bringing about both a nonlateralized reduction in VSTM capacity, as well as a lateralized spatio-attentional bias.…”

Thalamocortical excitability adjustments guide human perception under uncertainty

“…This component increased from selective attention to target load 2, but then declined towards higher loads. Decreases in angular gyrus have been strongly to increased visual working memory load (Sheremata, Somers, & Shomstein, 2018;Todd & Marois, 2004). Increases in DMN regions, in addition to decreased prefrontal activity suggest that this component reflects relative task disengagement towards high load conditions, while increases in lateral visual cortex may reflect increased entrainment, and lack of top-down inhibition.…”