- Design
- systematic review and meta-analysis of randomised sham-controlled trials, random-effects models, GRADE applied
- Population
- 357 patients with dementia across nine randomised controlled trials
- Primary outcome
- global cognition immediately after stimulation and at follow-up
- Effect
- immediate global cognition SMD 0.28 (95% CI 0.01-0.54, I² 39%); no significant effect at follow-up or on neuropsychiatric symptoms
Nine randomised trials totalling 357 patients with dementia compared transcranial alternating current stimulation with sham, pooled with random-effects models and graded for certainty. This is a non-invasive technique delivering oscillating current through scalp electrodes, and it is being marketed to families ahead of the evidence.
Immediately after stimulation, global cognition improved against sham with a standardised mean difference of 0.28 (95% CI 0.01-0.54), with moderate heterogeneity. Immediate recall, delayed recall and associative memory also improved. A physiological measure of cholinergic transmission, short-latency afferent inhibition, improved consistently across studies (mean difference 0.34, no heterogeneity). No serious adverse events occurred.
The negatives are as informative. There was no significant benefit at follow-up — the improvement did not outlast the stimulation period in the studies that looked. Neuropsychiatric symptoms, which are what families most often want addressed, did not improve. Executive function was inconclusive.
So what a clinician can say is fairly precise. There is a small, statistically detectable immediate effect on memory and global cognition, a plausible cholinergic mechanism behind it, no safety signal across 357 patients, and no evidence that anything persists. That is not a treatment, and it is not a reason to fund private courses of stimulation — which is the question families are increasingly arriving with. It is a reason to take the mechanism seriously and to read the larger trials the authors call for.
- Tell families the measured benefit was immediate and did not persist to follow-up in these trials
- Explain that neuropsychiatric symptoms, the commonest reason families seek help, did not improve
- Note the absence of serious adverse events across 357 patients when asked about safety
- Do not recommend privately funded courses of stimulation on this evidence
- Keep the established priorities in place — treating reversible contributors, review of anticholinergic burden, carer support
Why it matters
Families are being offered this privately, and the question is what to say when they ask.
Don't overread it
An immediate post-stimulation effect on a cognitive test is not evidence of clinical benefit, and nothing here persisted beyond the stimulation period.
The statistics, in plain English
A standardised mean difference of 0.28 is a small effect by convention, and its interval runs from 0.01 to 0.54 — the lower bound is essentially zero, so the finding only just clears no difference. Nine trials with 357 patients between them is a thin evidence base, and heterogeneous stimulation parameters mean the pooled estimate averages protocols that may differ substantially in effect. The absence of benefit at follow-up reflects both a genuine null and the fact that few studies collected follow-up data at all, which the authors flag.
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