A modulatory attentional gate promotes recent memory expression in Drosophila

Using short-term memory (STM) requires that animals can distinguish memories of recent experience from those learned previously. In Drosophila the neuromodulator octopamine (OA) specifically affects STM through adrenergic-like receptors within neurons in the Mushroom Body (MB) network. However, why OA preferentially impacts STM remains unclear. A fly brain connectome reveals that two OA-VPM3 neurons provide most OA input to the MB network. Artificial OA-VPM3 activation during olfactory learning enhances STM and can divert odor salience. α-adrenergic-like receptor knock-down in MB β and γ lobe MB Output Neurons (MBONs) generally impaired STM, while β-adrenergic-like receptor loss from α lobe MBONs enhanced memory. The identity and connectivity of the relevant MBONs suggests OA modulates an interaction between sites of STM and long-term memory (LTM) storage. Indeed, synthetic, odor, and learning-driven, OA-VPM3 activation temporarily blocks LTM expression. Therefore, OA reconfigures the MBON network so the fly prioritizes expression of recent over remote memories.