Anesthesia-resistant memory

Abstract: Two types of consolidated memory have been described in Drosophila, anesthesia-resistant memory (ARM), a shorter-lived form, and stabilized long-term memory (LTM). Until now, it has been thought that ARM and LTM coexist. On the contrary, we show that LTM formation leads to the extinction of ARM. Flies devoid of mushroom body vertical lobes cannot form LTM, but spaced conditioning can still erase their ARM, resulting in a remarkable situation: The more these flies are trained, the less they remember. We propose that ARM acts as a gating mechanism that ensures that LTM is formed only after repetitive and spaced training.

Abstract: MEMORY in many organisms can be disrupted by anaesthesia or electroconvulsive shock applied shortly after training. Later, if left undisturbed, the memory becomes immune to these agents. This suggests that learned information is stored by the brain in more than one form1–4. A population of Drosophila melanogaster can be trained to avoid an odorant by presenting the odour in combination with electric shock. When tested later without shock, the flies avoid this odorant specifically (ref. 5 and unpublished results of Y.D.). By anaesthetising the flies briefly with cold at various times between training and testing, we have found two memory components in Drosophila.

Abstract: A fundamental duty of any efficient memory system is to prevent long-lasting storage of poorly relevant information. However, little is known about dedicated mechanisms that appropriately trigger production of long-term memory (LTM). We examined the role of Drosophila dopaminergic neurons in the control of LTM formation and found that they act as a switch between two exclusive consolidation pathways leading to LTM or anesthesia-resistant memory (ARM). Blockade, after aversive olfactory conditioning, of three pairs of dopaminergic neurons projecting on mushroom bodies, the olfactory memory center, enhanced ARM, whereas their overactivation conversely impaired ARM. Notably, blockade of these neurons during the intertrial intervals of a spaced training precluded LTM formation. Two pairs of these dopaminergic neurons displayed sustained calcium oscillations in naive flies. Oscillations were weakened by ARM-inducing massed training and were enhanced during LTM formation. Our results indicate that oscillations of two pairs of dopaminergic neurons control ARM levels and gate LTM.