Together, the distributed nature of VSTM and its overlap with visual attention processes calls into question whether VSTM activity in IPS reflects the maintenance or sustained attention necessary to hold objects in memory, or both.įunctional analyses of PPC can be impeded by the fact that spatially proximal areas may be functionally disparate. Even stimulus-specific delay period activity, arguably a VSTM function, might reflect sustained attention. Furthermore, change detection tasks, often used to study VSTM, rely upon attentional selection and evoke brain activation similar to attentional modulation ( Huettel et al., 2001 Gazzaley et al., 2007). Recent investigations, however, show that multiple cortical areas carry information about remembered items ( Harrison and Tong, 2009 Serences et al., 2009 Riggall and Postle, 2012 Ester et al., 2015 Bettencourt and Xu, 2016). Early studies indicated a central role of IPS in encoding and maintaining VSTM representations ( Todd and Marois, 2004 Xu and Chun, 2006), demonstrating that IPS activity reflects the number of items held in memory.
Studies of VSTM offer a clear example of the difficulty in isolating the relevant cognitive mechanisms within the IPS. Disentangling discrete cognitive mechanisms is rendered difficult by numerous cognitive functions subserved by the PPC.
The intraparietal sulcus (IPS) of posterior parietal cortex (PPC) has been implicated in a wide variety of cognitive tasks including visual attention ( Corbetta and Shulman, 2002), visual short-term memory (VSTM Todd and Marois, 2004 Xu and Chun, 2006), enumeration ( Dehaene et al., 2003), perceptual decision-making ( Freedman and Assad, 2006), long-term memory retrieval ( Sestieri et al., 2017), and motor planning ( Oristaglio et al., 2006). Our study fills a gap in the literature by directly comparing and controlling for overlap between visual attention and 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. 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. Cognitive mechanisms and neural activity underlying these tasks show a large degree of overlap. SIGNIFICANCE STATEMENT Visual short-term memory (VSTM) and attention are distinct yet interrelated processes. 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. 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. This divergence between tasks demonstrates that parietal activation reflects memory-specific functions and consequently modulates functional connectivity across the cortex.
Contrasting VSTM and attention, intraparietal sulcus (IPS) 1–2 were more strongly connected with anterior frontoparietal areas and more weakly connected with posterior regions. Additionally, the tasks differentially modulated parietal functional connectivity. Relative to attention, VSTM increased BOLD amplitude in dorsal parietal cortex and decreased BOLD amplitude in the angular gyrus. While attention and VSTM activated similar cortical areas, BOLD amplitude and functional connectivity in parietal cortex differentiated the two tasks. 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. 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. While both require selection of information across the visual field, memory additionally requires the maintenance of information across time and distraction. Visual short-term memory (VSTM) and attention are distinct yet interrelated processes.
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