Dissociable causal roles for left and right parietal cortex in controlling attentional biases from the contents of working memory

Abstract

The contents of working memory (WM) steer visual attention, but the extent of this guidance can be strategically enhanced or inhibited when WM content is reliably helpful or harmful to a visual task. Current understanding of the neural substrates mediating the cognitive control over WM biases is limited, however, by the correlational nature of functional MRI approaches. A recent fMRI study provided suggestive evidence for a functional lateralization of these control processes in posterior parietal cortex (PPC): activity in left PPC correlated with the presentation of WM cues that ought to be strategically enhanced to optimize performance, while activity in the right PPC correlated with the presentation of cues that ought to be inhibited to prevent detrimental attentional biases in a visual search. Here, we aimed to directly assess whether the left and right PPC are causally involved in the cognitive control of WM biases, and to clarify their precise functional contributions. We therefore applied 1Hz repetitive transcranial magnetic stimulation (rTMS) to left and right PPC (and a vertex control site) prior to administering a behavioral task assessing WM biasing control functions. We observed that the perturbation of left PPC eliminated the strategic benefit of predictably helpful WM cueing, while the perturbation of right PPC amplified the cost of unpredictable detrimental WM cueing. Left and right PPC thus play distinct causal roles in WM-attention interactions: left PPC to maximize benefits, and right PPC to minimize costs, of internally maintained content on visual attention.

Evaluating the Role of the Dorsolateral Prefrontal Cortex and Posterior Parietal Cortex in Memory-Guided Attention With Repetitive Transcranial Magnetic Stimulation

“…As hypothesized we showed that, compared with the vertex-TMS, TMS to the rPPC disrupted the suppression of irrelevant WM content, leading to faster search RTs in the valid condition. These findings extend those of an earlier study in which the left PPC was found to enhance the benefits of valid WM cues ( Kiyonaga et al, 2014 ).…”

“…The vertex was selected as a control site for non-specific disruption of search performance due to concurrent discomfort, tactile sensations over the scalp, stimulation noise and muscle twitches. Since the motor cortex excitability does not provide reliable TMS thresholds in other cortical areas ( Stewart et al, 2001 ; Muggleton et al, 2011 ; Kiyonaga et al, 2014 ), we did not use it as a reference for stimulus intensity. Stimulation intensity was delivered at a fixed intensity of 45% of the maximum stimulator output.…”

Center-Surround Inhibition in Working Memory

“…That this pattern is not evident here may be explained by the fact that facilitation from WM-matching targets and inhibition from WM-matching distractors have been suggested to occur by qualitatively distinct mechanisms [31]–[34], so we would not necessarily expect the modulation of both to be equal. Intriguingly, furthermore, the release from suppression observed in Experiment 1 corresponds to the distance of non-matching probes from the WM sample (i.e., 30°) which would dictate the specificity of WM discrimination necessary to perform well on catch trials.…”

Selective inhibition of distracting input

“…St. John-Saaltink and colleagues have suggested that expectation and working memory rely on common processes to reinstate stimulus templates in visual cortex, with expectation mechanisms using these stimulus templates to compare subsequent bottom-up input. Indeed, a distinct set of posterior parietal regions are engaged when working memory contents is predicted to match targets and when working memory is predicted to match subsequent distractor items [78,79]. Again, these effects could potentially suggest a degree of flexible control over working memory based control, or at least an interaction between expectation and working memory.…”