Modulation of the executive control network by anodal tDCS over the left dorsolateral prefrontal cortex improves task shielding in dual tasking

Mahesan, Devu; Antonenko, Daria; Flöel, Agnes; Fischer, Rico · 2023 · Crossref

DOI: 10.1038/s41598-023-33057-7

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Summary

This study investigates whether anodal transcranial direct current stimulation (atDCS) over the left dorsolateral prefrontal cortex (dlPFC) can enhance task shielding, an executive control process that minimizes interference between simultaneous tasks. While neuroimaging links dlPFC activity to multitasking, the causal role of this region in task shielding and the potential of non-invasive brain stimulation to facilitate it remained unclear. The authors hypothesized that increasing cortical excitability in the left dlPFC would improve the segregation of stimulus-response processes, thereby reducing between-task interference. The research employed a single-blind, crossover, sham-controlled design with 34 healthy participants. Each participant completed two sessions separated by approximately seven days, receiving either atDCS (1 mA for 20 minutes) or sham stimulation (1 mA for 30 seconds) over the left dlPFC. Participants performed a dual-task paradigm consisting of a visual discrimination task (Task 1) and an auditory discrimination task (Task 2). To induce crosstalk, the tasks shared processing similarities and response mappings. Temporal overlap was manipulated using three stimulus onset asynchronies (SOAs): 40, 130, and 300 ms. Task shielding was assessed via the backward crosstalk effect (BCE), measured by differences in error rates and response times between compatible and incompatible trials. Results indicated that atDCS significantly reduced between-task interference in error rates for Task 1, particularly under conditions of high temporal overlap. In the sham condition, the BCE was significant at short SOAs (40 and 130 ms), reflecting typical interference. However, atDCS eliminated this backward crosstalk at the shortest SOA (40 ms), demonstrating improved task shielding when multitasking demands were highest. No significant differences were found in response times between stimulation conditions, nor were there significant effects on Task 2 performance metrics. The study confirmed effective blinding, with participants guessing the stimulation condition at chance levels, and reported no significant differences in side effects between atDCS and sham conditions. These findings provide causal evidence that the left dlPFC plays a critical role in task shielding and that its modulation via atDCS can improve executive control during dual-tasking. The results suggest that non-invasive brain stimulation can specifically enhance the shielding of prioritized task processing, particularly in scenarios vulnerable to interference. This extends previous correlational neuroimaging studies by demonstrating that enhancing excitability in the left-lateralized executive control network facilitates conflict resolution and reduces crosstalk, offering a potential tool for improving multitasking performance in contexts requiring high executive control.

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• dual task multitasking