DNA methylation adjusts the specificity of memories depending on the learning context and promotes relearning

11 The activity of the epigenetic writers DNA methyltransferases (Dnmts) after olfactory reward 12 conditioning is important for both stimulus-specific long-term memory (LTM) formation and 13 extinction. It, however, remains unknown which components of memory formation Dnmts 14 regulate (e.g. associative vs. non-associative) and in what context (e.g. varying training 15 conditions). Here we address these aspects in order to clarify the role of Dnmt-mediated 16 DNA methylation in memory formation. We used a pharmacological Dnmt inhibitor and 17 classical appetitive conditioning in the honeybee Apis mellifera, a well characterized model 18 for classical conditioning. We quantified the effect of DNA methylation on naïve odour and 19 sugar responses, and on responses following olfactory reward conditioning. We show that 20 (1) Dnmts do not influence naïve odour or sugar responses, (2) Dnmts do not affect the 21 learning of new stimuli, but (3) Dnmts influence odour-coding, i.e. 'correct' (stimulus22 specific) LTM formation. Particularly, Dnmts reduce memory specificity when experience is 23 low (one-trial training), and increase memory specificity when experience is high (multiple24 trial training), generating an ecologically more useful response to learning. (4) In reversal 25 learning conditions, Dnmts are involved in regulating both excitatory (re-acquisition) and 26 inhibitory (forgetting) processes. 27