Scientists at the University of Tubingen said those slow oscillations in brain activity, which occur during so-called slow-wave sleep, are critical for retaining memories.
Matching sounds to the oscillations can provide an easy and noninvasive way to influence human brain activity to improve sleep and enhance memory, they said.
"The beauty lies in the simplicity to apply auditory stimulation at low intensities -- an approach that is both practical and ethical, if compared for example with electrical stimulation -- and therefore portrays a straightforward tool for clinical settings to enhance sleep rhythms," study co-author Jan Born said.
In tests, sleeping volunteers exposed to stimulating sounds in sync with the brain's slow oscillation rhythm were better able to remember word associations they had learned the evening before, the researchers said.
The technique might also be used more generally to improve sleep, they said.
The study was published in the journal Neuron.