Theta oscillations dictate the evolution of memories across periods of sleep or wakefulness

Every day, we are exposed to an enormity of information. But how does the brain select which experiences to strengthen into long-term memories? Using scalp electroencephalography in human participants, we find evidence that memories are tagged at encoding for selective strengthening across sleep or wakefulness. For memories retained over sleep, this process was driven by 3-8 Hz theta rhythms at learning, with the magnitude of this theta response predicting the coupling of slow oscillations to sleep spindles in later sleep (an established neural correlate of sleep-dependent memory processing). In turn, slow oscillation-spindle coupling was associated with superior memory retention at a post-sleep test. These findings offer new insights into the neural mechanisms through which our brains determine which information is retained for the future.