(A) Schematic diagram of the Drosophila melanogaster mushroom body showing the compartments innervated by dopaminergic neurons (DANs) that induce positive memories (light/dark blue) and negative memories (light/dark pink), and the neurons studied by Aso et al.: PAM-γ5/PAM-β’2a (dark blue) and PPL1-γ1pedc (dark pink). (B) Nitric oxide synthase (NOS) generates nitric oxide (NO, red dots) in a dopaminergic neuron (DAN, top). NO diffuses into the Kenyon cell (KC, bottom), where it binds soluble guanylate cyclase (sGC) to produce an ‘inverted’ memory. At the same time, dopamine (DA, blue dots) is released from the dopaminergic neuron via synaptic vesicles, creating a ‘normal’ memory. (C) NO-induced memories (middle) have the opposite valence to dopamine-induced memories (top) and are slower to both form and decay. Dopamine and NO interact (bottom) to produce memories that form and decay quickly and are easily updated.