Abstract
Working memory (WM) is a fundamental cognitive ability to support complex thought, but it is limited in capacity. WM training has shown the potential benefit for those in need of a higher WM ability. Many studies have shown the potential of transcranial direct current stimulation (tDCS) to transiently enhance WM performance by delivering a low current to the brain cortex of interest, via electrodes on the scalp. tDCS has also been revealed as a promising intervention to augment WM training in a few studies. However, those few tDCS-paired WM training studies, focused more on the effect of tDCS on WM enhancement and its transferability after training and paid less attention to the variation of cognitive performance during the training procedure. The current study attempted to explore the effect of tDCS on the variation of performance, during WM training, in healthy young adults. All the participants received WM training with the load-adaptive verbal N-back task, for 5 days. During the training procedure, active/sham anodal high-definition tDCS (HD-tDCS) was used to stimulate the left dorsolateral prefrontal cortex (DLPFC). To examine the training effect, pre- and post-tests were performed, respectively, 1 day before and after the training sessions. At the beginning of each training session, stable-load WM tasks were performed, to examine the performance variation during training. Compared to the sham stimulation, higher learning rates of performance metrics during the training procedure were found when WM training was combined with active anodal HD-tDCS. The performance improvements (post–pre) of the active group, were also found to be higher than those of the sham group and were transferred to a similar untrained WM task. Further analysis revealed a negative relationship between the training improvements and the baseline performance. These findings show the potential that tDCS may be leveraged as an intervention to facilitate WM training, for those in need of a higher WM ability.
Highlights
This study examined the effect of anodal HD-Transcranial direct current stimulation (tDCS) on the variation of performance during load-increasing working memory (WM) training
high-definition tDCS (HD-tDCS) was paired with a five-session WM training task
The results showed that learning rates and training gains of the performance metrics, benefited from anodal HD-tDCS of left dorsolateral prefrontal cortex (DLPFC)
Summary
Like working memory (WM) training, has shown the potential to produce broad benefits for those who have special requirements in their cognitive abilities, or for those who suffer from cognitive impairments (Richmond et al, 2014; Au et al, 2016; Choe et al, 2016; Stephens and Berryhill, 2016; Ciechanski and Kirton, 2017; Ruf et al, 2017; Talsma et al, 2017). These findings indicate that the enhancing effect of tDCS on WM memory depends on the stimulation polarity and is specific to the site of stimulation (Fregni et al, 2005). Many subsequent studies compared factors like electrode placement, current density and stimulation duration that may affect the efficacy of tDCS and found that the anodal stimulation of the left prefrontal, tended to enhance WM performance (Coffman et al, 2014; Richmond et al, 2014; Moreno et al, 2015; Santarnecchi et al, 2015; Au et al, 2016; Gözenman and Berryhill, 2016; Hill et al, 2016a, 2017; Stephens and Berryhill, 2016; Trumbo et al, 2016; Ruf et al, 2017; Talsma et al, 2017). In addition to WM related studies, tDCS has shown potential to mitigate vigilance decrement (Nelson et al, 2014) and enhance multitasking performance (Nelson et al, 2016)
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