Abstract

Background: Personnel in special occupations generally need to continuously maintain a high level of cognitive control and attention and respond quickly to unpredictable stimuli at daily work. This continuous high mental workload (HMW) and stress state can lead to the occurrence of Mental fatigue (MF). Currently, more and more studies are using transcranial direct current stimulation (tDCS) to intervene in MF, but the effects of the intervention are mixed. Researchers believe such results may result from the vast majority of studies with only one intervention. It was shown that tDCS combined with transcutaneous auricular vagus nerve stimulation (taVNS) produced a significant synergistic effect on brain responses. Thus, repeated tDCS combined with taVNS may greatly enhance individual cognitive performance and resistance to MF. However, no empirical evidence exists for the effects of repeated tDCS combined with tAVNS and tDCS on enhancing individual resistance to MF. Therefore, this study aims to explore the short- and long-term effects of repeated tDCS combined with taVNS and tDCS on enhancing individual resistance to MF, to provide preliminary programmatic and empirical evidence for the application of neuromodulation to the anti-MF aspects of individuals.

Methods: A randomized double-blind sham stimulation-controlled experimental design was used. Seventy-two young male adults were randomized to the tDCS combined with tAVNS group (n = 24), the tDCS group (n = 24), and the sham stimulation group (n = 24) and received the corresponding repetitive stimulation intervention method (2 stimulations per day for 3 days, with two stimulations per day spaced at least 4 hours apart, each stimulation being 30 min). Cognitive tasks and subjective scales were assessed at a total of 4 time points before the intervention (1 day after the intervention, 1 week after the intervention, and 1 month after the intervention). Data were analyzed using repeated measures ANOVA.

Results: The tDCS, taVNS, tDCS, and Sham repetitive stimulation methods were all effective in reducing the incremental subjective MF generated during task performance, enhancing the number of correct trials, and maintaining some long-term effects. The tDCS combined with the taVNS method enhanced the number of correct trials more effectively than the tDCS and Sham schemes.

Conclusion: Repeated tDCS combined with taVNS can be an essential intervention to enhance individuals' resistance to MF and cognitive ability.