Our brains keep on whirling long after we drift off to sleep. Each night, the hippocampus, a major hub for learning, replays experiences from the previous day and etches them into memory. And even in deep sleep, neurons in sensory regions of the brain spark with activity when they receive new stimuli, like sounds. This raises a provocative question: How much is consciousness required to make sense of the world around us? A new study suggests the unconscious brain can handle far more than simple sensory cues. Recording electrical activity from patients under general anesthesia, a team at Baylor College of Medicine and collaborators found the hippocampus continued processing sounds, words, and speech while patients listened to alternating tones and podcast clips. Groups of neurons shifted their activity depending on the type of word spoken—nouns or verbs, for example—and predicted the next word in sentences.…