Training-induced cognitive coupling emerges under sham but not active transcranial electrical stimulation in older adults: a triple-blind, randomized, sham-controlled study.
Yong Jiang, Xue Guo, Isabella Wistuba and 4 others
Ten sessions of tDCS or tACS added to cognitive and balance training did not improve attention or executive function beyond the training alone in healthy older adults.
The sham group showed the largest gains on several attention measures.
Key findings
1No stimulation group outperformed the sham group on any attention or executive function measure. The sham + training group showed the largest gains in central-cue, double-cue, and spatial-cue reaction times on the Attention Network Test.
2All three groups improved in executive control efficiency and on the Stroop Color-Word Test over time, with no between-group differences. The authors attribute these gains to the training rather than the stimulation.
3Participants could not guess their stimulation condition (34.5% correct, below the 50% chance level), and side effects were mild, transient, and similar across groups.
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What it does not show
No training-only control group was included (it was removed before data collection to preserve blinding), so the relative contributions of task training and sham stimulation, including placebo and expectation effects, cannot be separated. The paper reports pre-registered secondary outcomes, not the primary endpoint of the registered trial. All participants were healthy older adults with MoCA scores of 26 or higher, so the findings do not extend to people with cognitive impairment or neurodegenerative disease. Baseline accuracy was already near ceiling in several conditions (e.g., 98–99% in the active stimulation groups), which may have limited room for further improvement. Participants' expectations about the intervention were not formally assessed, and the authors note that expectation-driven effects may have influenced the sham group's performance. No EEG or fMRI was used, so the neural mechanisms underlying the behavioral changes are unknown.
Declared interests
Funded by Herzzentrum Göttingen (grant 1018). No other conflicts of interest are declared in the text provided.
The easy way to misread this
Do not read this as evidence that tDCS or tACS are ineffective for cognition. The study tested them only in combination with training, in healthy older adults, and reports pre-registered secondary outcomes rather than the primary endpoint. The sham group's larger gains may reflect expectation or placebo effects rather than a true advantage of sham over active stimulation.
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