WASHINGTON (Dispatches) --  University of Michigan research suggests that groups of neurons activated during prior learning keep humming, tattooing memories into your brain.
The researchers have been studying how memories associated with a specific sensory event are formed and stored in mice. They 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.
The researchers found that when they disrupted sleep after they showed the subjects an image and had given them a mild foot shock, there was no fear associated with the visual stimulus. Those with unmanipulated sleep learned to fear the specific visual stimulus that had been paired with the foot shock.