Transcranial electrical stimulation has widespread clinical and research applications, yet its
effect on ongoing neural activity in humans is not well established. Previous reports argue
that transcranial alternating current stimulation (tACS) can entrain and enhance neural
rhythms related to memory, but the evidence from non-invasive recordings has remained
inconclusive. Here, we measure endogenous spindle and theta activity intracranially in
humans during low-frequency tACS and find no stable entrainment of spindle power during …