Anodal tDCS augments and preserves working memory beyond time-on-task deficits

Abstract

Transcranial direct current stimulation (tDCS) of the left dorsolateral prefrontal cortex (DLPFC) has been shown to promote working memory (WM), however, its efficacy against time-on-task-related performance decline and associated cognitive fatigue remains uncertain. This study examined the impact of anodal tDCS of the left DLPFC on performance during a fatiguing visuospatial WM test. We adopted a repeated measures design, where 32 healthy adults (16 female), underwent anodal, control and sham tDCS on separate days. They completed an hour long two-back test, with stimulation intensity, onset, and duration set at 1 mA, at the 20th minute for 10 minutes respectively. Task performance, subjective responses, and heart rate variability (HRV) were captured during the experiment. Anodal tDCS substantially improved WM relative to sham tDCS and control in both sexes. These benefits lasted beyond the stimulation interval, and were unique across performance measures. However, no perceptual changes in subjective effort or fatigue levels were noted between conditions, although participants reported greater discomfort during stimulation. While mood and sleepiness changed with time-on-task, reflecting fatigue, these were largely similar across conditions. HRV increased under anodal tDCS and control, and plateaued under sham tDCS. We found that short duration anodal tDCS at 1 mA was an effective countermeasure to time-on-task deficits during a visuospatial two-back task, with enhancement and preservation of WM capacity. However, these improvements were not available at a perceptual level. Therefore, wider investigations are necessary to determine “how” such solutions will be operationalized in the field, especially within human-centered systems.

The therapeutic potential of non-invasive brain stimulation for the treatment of Long-COVID-related cognitive fatigue

“…In healthy participants, anodal tDCS over the left DLPFC reduced vigilance deficits caused by sleep deprivation and improved subjective state fatigue scores ( 107 – 109 ). Furthermore, anodal tDCS sustained or even improved the working memory performance in an hour-long two-back task ( 110 ). Recently, we showed that a single dose of anodal tDCS successfully counteracted fatigability development in healthy participants and, in turn, reduced the increase in occipital alpha power and the decline in sensory gating resulting from fatigability ( 66 ).…”

Boosting working memory: uncovering the differential effects of tDCS and tACS

“…The study showed small improvements in hit rates and reductions in error rates for the tDCS compared with the sham control condition. In another study, Karthikeyan et al. (2021) examined effects of tDCS over the DLPFC in a fatiguing visuospatial n -back task.…”

“…Sixteen out of the 23 single-session tDCS experiments included in this review were published in the last 5 years, i.e., 2017–2021. Only 2 of them showed effects of tDCS on WM ( Karthikeyan et al. 2021 ; Schmicker et al.…”

“…While the majority of reviewed studies did not report effects, there is some evidence that tDCS may be capable of influencing WM performance when the task is highly demanding ( Fregni et al. 2005 ; Karthikeyan et al. 2021 ).…”

Comparing the efficacy of AR-based training with video-based training

“…Physiological measures: The raw ECG signal taken at 128 Hz was preprocessed to remove any motion artifacts and the peak detection algorithm was used, R-peaks from the signal were collected (Karthikeyan et al, 2021). The root mean square of successive differences (RMSSD) and low-to-high frequency ratio (LF/HF) were the two HRV features extracted to detect variations in cognitive load.…”