Memory-forming chemical reactions.

We address in this review the various types of chemical reactions that underlie memory storage in biological systems. Using examples from both invertebrate and mammalian learning systems, we describe three types of memory-storing reactions: short-term reactions mediated by transient changes in second messenger levels, long-term reactions mediated by species with long half lives, and ultralong-term or mnemogenic reactions that can store memory indefinitely, even in the face of ongoing turnover of the molecules involved.