Parietal Contributions to Visual Working Memory Depend on Task Difficulty

Abstract

The nature of parietal contributions to working memory (WM) remain poorly understood but of considerable interest. We previously reported that posterior parietal damage selectively impaired WM probed by recognition (Berryhill and Olson, 2008a). Recent studies provided support using a neuromodulatory technique, transcranial direct current stimulation (tDCS) applied to the right parietal cortex (P4). These studies confirmed parietal involvement in WM because parietal tDCS altered WM performance: anodal current tDCS improved performance in a change detection task, and cathodal current tDCS impaired performance on a sequential presentation task. Here, we tested whether these complementary results were due to different degrees of parietal involvement as a function of WM task demands, WM task difficulty, and/or participants’ WM capacity. In Experiment 1, we applied cathodal and anodal tDCS to the right parietal cortex and tested participants on both previously used WM tasks. We observed an interaction between tDCS (anodal, cathodal), WM task difficulty, and participants’ WM capacity. When the WM task was difficult, parietal stimulation (anodal or cathodal) improved WM performance selectively in participants with high WM capacity. In the low WM capacity group, parietal stimulation (anodal or cathodal) impaired WM performance. These nearly equal and opposite effects were only observed when the WM task was challenging, as in the change detection task. Experiment 2 probed the interplay of WM task difficulty and WM capacity in a parametric manner by varying set size in the WM change detection task. Here, the effect of parietal stimulation (anodal or cathodal) on the high WM capacity group followed a linear function as WM task difficulty increased with set size. The low WM capacity participants were largely unaffected by tDCS. These findings provide evidence that parietal involvement in WM performance depends on both WM capacity and WM task demands. We discuss these findings in terms of alternative WM strategies employed by low and high WM capacity individuals. We speculate that low WM capacity individuals do not recruit the posterior parietal lobe for WM tasks as efficiently as high WM capacity individuals. Consequently, tDCS provides greater benefit to individuals with high WM capacity.

Modulation of attention functions by anodal tDCS on right PPC

“…Considering the complexity of the model of three independent attention networks the ANT comprises, a separation of, e.g., low vs. high performing individuals based upon the ANT data is not as straight forward as in the study by Jones and Berryhill (2012) mentioned above and our subject number was too small for a valid multifactorial analysis.…”

“…In participants with high working memory (WM) capacity, Jones and Berryhill (2012) uncovered selective effects of rPPC tDCS (anodal or cathodal) when WM task difficulty was increased: In the high WM capacity group, the effect of PPC tDCS (anodal or cathodal) followed a linear function as WM task difficulty increased with set size, while in the low WM capacity group, PPC tDCS (anodal or cathodal) impaired WM performance (Exp 1) or left it unchanged (Exp 2). The authors speculated that low WM capacity individuals may not recruit the PPC for WM tasks as efficiently as high WM capacity individuals.…”

Transcranial Electrical Stimulation as a Tool to Enhance Attention

“…Anodal stimulation over the right inferior frontal cortex has consistently shown to speed up object detection. Perhaps this success can be attributed to the challenging nature of the task: tES effects might be greatest for difficult tasks with plenty of room for improvement (e.g., Jones and Berryhill 2012). Because this task is more complex than the typical visual search paradigm, it could also be that tDCS affected other processes such as threat detection or scene perception, and not those underlying visual search per se.…”

Effect of prefrontal and parietal tDCS on learning and recognition of verbal and non-verbal material

“…However, recent studies also report a drop in performance following anodal tDCS (Ferrucci et al, 2008;Jones and Berryhill, 2012;Kaminski et al, 2013;Zwissler et al, 2014;Schaal et al, 2015) or improvements following cathodal tDCS (Smirni et al, 2015). A recent tDCS study reported a significant decrease in performance in an old/new recognition task following anodal tDCS over the left PFC during encoding of pictures (Zwissler et al, 2014).…”