Neurons activated by visual stimulus keep more active during subsequent sleep, study shows When you slip into sleep, it's easy to imagine that your brain shuts down, but University of Michigan research suggests that groups of neurons activated during prior learning keep humming, tattooing memories into your brain. U-M researchers have been studying how memories associated with a specific sensory event are formed and stored in mice. In a study conducted prior to the coronavirus pandemic and recently published in Nature Communications, the researchers examined how a fearful memory formed in relation to a specific visual stimulus. They found that not only did the neurons activated by the visual stimulus keep more active during subsequent sleep, sleep is vital to their ability to connect the fear memory to the sensory event.