A single session of online tDCS over the left dorsolateral prefrontal cortex improves visual working memory

Background: Previous studies have mainly demonstrated the overall effect of transcranial direct current stimulation (tDCS) on working memory (WM). However, the segregative effects of offline and online tDCS over the left dorsolateral prefrontal cortex (dlPFC) and on the subtypes within WM are still under debate. Here, the present research explores that one session of online and offline anodal tDCS over left dlPFC has the potential to improve different aspects of WM performance. Methods: Twenty-eight participants were randomized to receive 20 min of either anodal (1.5 mA) or control (sham) tDCS applied to the left dlPFC in a randomized, double-blind design. Visual WM was evaluated through the Sternberg task and by manipulating stimuli congruency and cognitive load during online (i.e., ongoing stimulation) application of tDCS, whereas verbal episodic WM (Selective Reminding Test and Direct Digits) was assessed during offline (i.e., after-effects) application of tDCS. Results: After real anodal tDCS but not sham stimulation, participants significantly improved WM performance by reducing reaction times and increasing accuracy in the Sternberg task during online application of tDCS, particularly for those task conditions with higher cognitive demands. Overall, the real anodal tDCS group was 10% more accurate than the sham group after one single session of tDCS. No significant effects were detected during the assessment of short-term verbal memory after the offline application of tDCS. Conclusions: These findings support the idea that one single online session of tDCS over left dlPFC can impact short-term visual memory predominantly under higher cognitive load and suggest that tDCS may improve WM performance when dlPFC networks become overtaxed by cognitive demands or when more complex cognitive processes are required. Our findings can contribute to the development of effective tDCS protocols that can be applied to the treatment of clinical populations with WM deficits. Research Category and Technology and Methods Basic Research: 9. Transcranial Direct Current Stimulation (tDCS) Keywords: Transcranial direct current stimulation, Working memory, Dorsolateral prefrontal cortex