?Limbo? state of memory: identification and characterisation of a new retrievaldependent memory process in the crab Neohelice granulata.

MERLO SANTIAGO; M JIMENA SANTOS*; EMILIANO MERLO; ME PEDREIRA

Cordoba

Congreso; XXXIII Congreso SAN; 2018

SAN

In aversive Pavlovian conditioning, contingent presentation of a neutral stimulus (conditioned stimulus,CS) and a negative outcome (unconditioned stimulus, US) results in the formation of a CS-US fear memory.Thus, the presentation of the CS alone triggers a conditioned response (CR). Fear memory persistencecould be differentially affected by retrieval. Brief CS exposures trigger memory reconsolidation and CRmaintenance, whereas exposure to a high number of CSs triggers extinction and CR inhibition. Bothreconsolidation and extinction have been characterised at the molecular level, presenting specificmechanisms for each process in vertebrates and invertebrates. Here we tested the hypothesis thatintermediate CS exposure sessions fail to engage either fear memory reconsolidation or extinction incrabs. Our results show that, whereas 1 or 40 CS presentations rendered the fear memory sensitive to theamnestic agent cycloheximide, 80 CSs failed to do so and were insufficient to trigger memory extinction.These results indicate that intermediate CS presentations leave the original memory in an insensitive or"limbo" state, characterised by the absence of behavioural effect of the amnestic agent cycloheximide.Considering that ?limbo? has been also reported in rodents and humans, our results strongly suggest thatit is an evolutionary conserved retrieval-dependent mechanism whose fundamental condition is the arrestof the memory labilisation process initiated by the first CSs.