«Importantly, the sound stimulation is effective only when the sounds occur in synchrony with the ongoing slow oscillation rhythm during deep sleep. (sciencedaily.com)
Although there were a few earlier hints, the first clear description of regular slow oscillations in the hippocampal EEG came from a paper written in German by Jung and Kornmüller (1938). (en.wikipedia.org)
This is the first study to show that artificial thalamic spindles affect memory, if administered in sync with slow oscillations. (sciencedaily.com)