Transcranial electrical stimulation improves cognitive training effects in healthy elderly adults with low cognitive performance.

Objective: To investigate the efficacy of transcranial direct (tDCS) or alternating current stimulation (tACS) in boosting cognitive training efficiency in healthy older adults. We further explored whether such improvements depend on general cognitive performance or age.

Methods: In this randomized, sham-controlled study, 59 healthy elderly participants (mean age 71.7) were assigned to receive computer-based cognitive training (10 sessions, 50 min, twice weekly) combined with tDCS (2 mA), tACS (5 Hz), or sham stimulation over the left dorsolateral prefrontal cortex (20 minutes). Cognitive performance was assessed with the Montreal Cognitive Assessment (MoCA), and a cognitive composite score derived from a broad neuropsychological test battery before and immediately after the intervention as well as at 6 and 12 months follow-ups.

Results: Performance in the cognitive composite score improved significantly in all groups but was not further modulated by neurostimulation. Additional analyses revealed that participants with a low initial MoCA score (<1SD) improved significantly more in the tDCS than in the sham group.

Conclusion: TDCS increased the efficacy of cognitive training, but only in participants with initially low general cognitive performance.

Significance: Cognitive interventions including tDCS should address baseline performance as modulating factor of cognitive outcomes.