Cold and lithium delay forgetting of olfactory memories in Caenorhabditis elegans.

The persistence of memory reflects not only how it is formed but also how forgetting is delayed. The mechanisms controlling forgetting remain obscure, and in particular it is unclear to what degree this process is actively regulated. We discovered that cold exposure delays forgetting of specific olfactory memories by more than eight-fold and that adaptation to cold abolishes this effect. To study the underlying mechanism, we performed RNA sequencing, mutant analyses and pharmacological assays. Here we show that regulation of membrane properties underlies the presence and absence of cold-induced delayed forgetting. Furthermore, lithium can also delay forgetting in cold-sensitive worms but not in cold-tolerant worms; this effect involves downregulation of the diacylglycerol pathway in AWC neurons and long-term suppression of activity in the downstream AIY interneurons. Thus, the genetic tractability of worms might be harnessed to study the mechanism of action of lithium and cold exposure and, more fundamentally, how memory is stored and lost.