Theta oscillations tag episodic memories for sleep-dependent consolidation.

How does the brain select which experiences to consolidate into long-term memory? Numerous neurobiological frameworks suggest that certain memories are "tagged" at learning for consolidation during later sleep. However, experimental evidence of such a tagging mechanism in the human brain is lacking. Employing multivariate classification of human electroencephalography data, we reliably decoded brain states for episodic memories that are tagged at learning for consolidation across sleep or wakefulness. The tagging of memories for consolidation across sleep (but not wakefulness) was linked to 3-8 Hz theta rhythms during learning. The magnitude of this tagging-related theta response predicted the coupling of slow oscillations to sleep spindles during post-learning sleep (an established neural correlate of sleep-dependent memory processing). In turn, slow oscillation-spindle coupling was associated with better memory performance at the post-sleep test. These findings provide new insights into the neural mechanisms through which our brains determine which information is retained for the future.