What makes for a long-lasting memory? Research has shown that emotional or important events become deeply rooted, whereas neutral ones create weak impressions that easily fade. But what about an experience that initially seemed forgettable but was later shown to be important? Animal research suggested that these types of older memories could be strengthened, but until now scientists had not been able to replicate these findings in humans. New evidence suggests that our initially weak memories are maintained by the brain for a set period of time, during which they can be enhanced. In a recent study, psychologists at New York University showed 119 participants a set of images of tools and animals. A few minutes later the subjects saw a new set of images, with an electric shock paired with either tools or animals to increase the salience of one category. The participants' memories for both sets of images were then tested either six hours later, or the next day. Participants remembered images from the first series better if they belonged to the same category that was later paired with a shock. The findings suggest that even if an event does not seem meaningful when it occurs, a later cue signalling that the experience was important can enhance old memory.