Abstract:

The right dorsolateral prefrontal cortex (DLPFC) plays an important role in working memory. Previous neuroimaging and neurophysiological studies have found sustained and elevated DLPFC activity during working memory delay period. Meanwhile, the right DLPFC has been suggested to be more dominant in visuospatial than verbal working memory. While the causal evidence for the relationship between the right DLPFC and visual working memory is still rare.

Transcranial direct current stimulation (tDCS) and EEG were combined to investigate the causal relationship between the right DLPFC and processes of visual working memory. Forty participants performed a color change detection task with memory load of 4 items (load-4) or 6 items (load-6) while their electroencephalography (EEG) was recorded. Before they performed the tasks, either 15 min of 1.5 mA transcranial direct current stimulation (tDCS) or 30 s of 1.5 mA sham stimulation (SHAM) was applied over the right DLPFC. The participants were divided into two groups according to their working memory capacity increment from load-4 to load-6 in the sham condition, the group who gained more increment (the high potential group) under the sham condition also benefit more from the anodal tDCS over the right DLPFC, while the other group (the low potential group) did not show such effects.

To further explore the neural mechanisms, N2pc and SPCN were compared between different conditions. N2pc did not show any stimulating effects or load effects for both low and high potential groups. In contrast, although SPCN did not show significant main effects of load or stimulation, or their interaction for the low potential group, SPCN did show main effects of stimulation for high potential group. The amplitude of SPCN after tDCS over the right DLPFC was significantly larger than that after the sham stimulation under load-4 condition, which coincided with the behavioral findings, and further suggested the role of the right DLPFC in representing the memory information during retrieval.

In sum, anodal tDCS over the right DLPFC promoted visual working memory capacity of those who had more cognitive potential from easier task (load-4) to harder task (load-6). The present study confirmed the causal role of the right DLPFC in representing the visual working memory information during the retrieval period.

Key words: visual working memory, tDCS, right DLPFC, SPCN, working memory potential