Some memories get locked into our brains, persisting for decades. Others slip out by the next day. Researchers have found that the process of recalling a memory actually contributes to this process. When a recent event is recalled, it's possible to consolidate its memory, update it, or even eliminate it entirely. All of that happens when we're conscious. Memories can also get replayed while we sleep, which is thought to influence their long-term storage. A study released over the weekend suggests that recall during sleep has a completely different effect from conscious recall.