Long-term memory (LTM) is memory, store as meaning, that can last as little as a few days or as long as decades. It differs structurally and functionally from working memory or short-term memory, which ostensibly stores items for only around 20 seconds. Biologically, short-term memory is a temporary potentiation of neural connections that can become long-term memory through the process of rehearsal and meaningful association. The proposed mechanism by which short-term memories move into LTM storage is via long-term potentiation, which leads to a physical change in the structure of neurons. Notably, the time scale involved at each level of memory processing remains under investigation.