Objective:

To assess whether home-based tDCS + aCT improves reaction-time-based processing speed, measured via the Cogstate battery.

Background:

Processing speed deficits are among the earliest and most prevalent cognitive impairments in multiple sclerosis (MS). While prior work showed global cognitive benefits of transcranial direct current stimulation (tDCS) paired with online adaptive cognitive training (aCT), its impact on reaction-time-based processing speed has not been established.

Design/Methods:

In a previously reported sham-controlled RCT (NCT03838770), participants with MS and fatigue were randomized to receive 30 days (six weeks) of remotely supervised sessions of 20 min active (2.0 mA) or sham tDCS targeting the left dorsolateral prefrontal cortex, each paired with aCT delivered using Posit Science’s BrainHQ program. Simple, choice, and one-back working memory reaction time measures (Cogstate Detection [DET], Identification [IDN], and One Back [ONB] tasks) were administered at baseline and post treatment (active: n=54; sham: n=48). Paired samples t-tests and effect sizes were used to assess within- and between-group differences.

Results:

The active tDCS + aCT group showed significant improvements on DET (0.32 ± 0.83, p = .006) and ONB (0.29 ± 0.85, p = .013), with trends on IDN (p = .068) and ONB accuracy (p = .083). There were no significant changes in the group receiving sham tDCS. This indicates a specific benefit of active stimulation for reaction-time-based cognitive processing speed.

Conclusions:

Active tDCS combined with cognitive training led to moderate improvements in reaction-time-based processing speed. These findings support the use of remotely delivered tDCS + aCT to address slowed processing speed in MS, a core contributor to cognitive dysfunction.