The effect of transcranial direct current stimulation of dorsolateral prefrontal cortex on performing a sequential dual task: a randomized experimental study

Abedanzadeh, Rasool; Alboghebish, Saeed; Barati, Parisa · 2021 · DOAJ

DOI: 10.1186/s41155-021-00195-8

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Summary

This study investigates whether transcranial direct current stimulation (tDCS) of the dorsolateral prefrontal cortex (DLPFC) can enhance performance in sequential dual tasks, specifically by reducing the psychological refractory period (PRP). The PRP is a delay in processing a second stimulus when it follows closely behind a first, caused by a bottleneck in information processing capacity. The authors hypothesized that stimulating the DLPFC, a region associated with executive function and inhibitory control, would increase processing speed and attention capacity, thereby mitigating this delay. The researchers conducted a randomized, sham-controlled experimental study with 26 university students (average age 25.2 years). Participants were divided into experimental and sham groups. The experimental group received anodal tDCS (1.5 mA for 20 minutes) over the DLPFC, while the sham group received stimulation that was discontinued after 30 seconds. All participants performed a sequential dual-task Stroop test before and after stimulation. The task required participants to identify the ink color of two successive word-color pairs, ignoring the word meaning. The tasks were presented with two different stimulus-onset asynchronies (SOAs): 100 ms (short) and 900 ms (long), in both congruent and incongruent conditions. Reaction times for the first (RT1) and second (RT2) stimuli were recorded. The results indicated no significant differences between groups in the pre-test phase. However, post-test analysis revealed significant improvements in the experimental group. Mixed-ANOVA showed a significant main effect of group and significant interactions involving group, SOA, and congruency. Specifically, post-hoc t-tests demonstrated that the experimental group had significantly reduced reaction times for the second stimulus (RT2) compared to the sham group in both short (100 ms) and long (900 ms) SOAs, across both congruent and incongruent conditions. For instance, at the 100 ms SOA, the reduction in RT2 was highly significant for both congruent-congruent and incongruent-incongruent trials. The findings suggest that anodal tDCS of the DLPFC enhances information processing speed and attentional capacity, effectively reducing the psychological refractory period. The authors conclude that this stimulation facilitates the passage of stimuli through the processing bottleneck, likely by modulating neurotransmitter concentrations and cortical excitability. This study provides evidence that non-invasive brain stimulation can improve dual-task performance, with potential implications for cognitive enhancement and the treatment of disorders involving inhibitory control deficits.

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• dual task multitasking