Abstract
It is believed that long-term memory (LTM) cannot be formed immediately because it must go through a protein synthesis-dependent consolidation process. However, the current study uses Drosophila aversive olfactory conditioning to show that such processes are dispensable for context-dependent LTM (cLTM). Single-trial conditioning yields cLTM that is formed immediately in a protein-synthesis independent manner and is sustained over 14 days without decay. Unlike retrieval of traditional LTM, which requires only the conditioned odour and is mediated by mushroom-body neurons, cLTM recall requires both the conditioned odour and reinstatement of the training-environmental context. It is mediated through lateral-horn neurons that connect to multiple sensory brain regions. The cLTM cannot be retrieved if synaptic transmission from any one of these centres is blocked, with effects similar to those of altered encoding context during retrieval. The present study provides strong evidence that long-term memory can be formed easily without the need for consolidation.
Highlights
It is believed that long-term memory (LTM) cannot be formed immediately because it must go through a protein synthesis-dependent consolidation process
The results showed that blocking the release of neurotransmitter from TH-Gal4-labelled neurons impaired context-dependent LTM (cLTM) formation, suggesting that dopaminergic neurons (DANs) are required for cLTM encoding
To identify which brain regions are required for cLTM retrieval, we investigated the role of antennal lobe (AL) local neurons and projection neurons (PNs)
Summary
It is believed that long-term memory (LTM) cannot be formed immediately because it must go through a protein synthesis-dependent consolidation process. In the present work, we showed that the same singletrial training induces a latent memory component that lasts for at least 14 days without decaying Such component was formed immediately without the requirement of consolidation time or new protein synthesis. Formation and retrieval of all reported olfactory memory components, which are context independent, have involved MB neurons, with short-term memory being processed through the γ lobe and LTM through α/β lobe[7,29,30] while LH neurons are believed mainly to process innate information, such as innate avoidance and attraction[25,31] Such extensive understanding of the neural anatomy of olfactory memory, and of accessible genetic tools, allows to examine more closely the circuits that mediate cLTM retrieval
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