The Neural Mechanisms Of Visual Working Memory Storage And Distractor Suppression

Visual working memory(WM)has been taken as the important basis of higher cognitive functions.It temporarily maintains visual information in our brain for the various upcoming cognitive tasks(i.e.learning,comprehending,and reasoning).Besides,an individual's ability to suppress distractors in visual WM can predict their visual WM capacity,which is significantly correlated with the estimations of their fluid intelligence and academic performance.Therefore,exploring the neural mechanisms underlying visual WM storage and distractor suppression functions can help us understand the essence of visual WM and how visual WM supports various cognitive functions.The posterior parietal cortex(PPC)and the prefrontal cortex(PFC)have been demonstrated two critical brain areas supporting visual WM functions.However,it is still unclear the causal role of these two areas in visual WM functions.By combining the non-invasive electrical stimulation and the high temporal resolution EEG recording methods,the current study intends to explore the neural mechanisms of visual WM storage and distractor suppression by three steps: 1.establish the neural indexes of visual WM storage and distractor suppression;2.build the causal relationships between PPC and PFC with visual WM storage and distractor suppression functions;3.build the causal relationships between PPC and PFC with visual WM capacity and precision.By applying a sequential loading visual WM task,the results of Experiment 1 first demonstrated that the parietal contralateral delay activity represents visual working memory storage.Furthurmore,the results of Experiment 2 and Experiment 3 established the relationship between the prefrontal bias signal and visual WM distractor suppression by simultaneously presenting targets and distractors.To examine the causal role of the PPC and the PFC in visual WM storage and distractor suppression,Experiment 4 applied non-invasive transcranial direct current stimulation(tDCS)to these two brain areas,respectively.The results of Experiment 4 revealed that the PPC-stimulation significantly increased visual WM capacity,which was not discovered in PFC-stimulation condition.To further examine the causal role of PPC in visual WM capacity and precision,Experiment 5 adopted a continuous recall task which can measure visual WM capacity and precision simultaneously.The results of Experiment 5 demonstrated that PPC not PFC has a dominant and causal role in visual WM capacity,not precision.Moreover,the results of Experiment 6 revealed that this causal role was influenced by individual's WM capacity which is modulated by their encoding strategy.Altogether,the current study first revealed the neural indexes of visual WM storage and distractor suppression.Furthermore,the present results provide robust evidence supporting the dominant and causal role of the PPC in visual WM storage by creatively combining non-invasive electrical stimulation and EEG recording methods,even though we didn't find the causal role of the PFC in visual WM process.The findings of the current study are critical to helping us understand the brain network that supports visual WM and the specific function of PPC and PFC in this network.Moreover,visual WM functions are impaired in the aging group and in patients with cognitive disorders(for example,schizophrenia,major depression,and Parkinson's diseases).The current study revealed that a short period of non-invasive electrical stimulation effectively enhanced visual WM capacity,providing promising methods to increase visual WM ability in these groups.