Early and late memory encoding in the dorso-medial prefrontal cortex: challenging the standard systems consolidation theory

GONZALEZ, CAROLINA; KRAMAR, CECILIA; GARAGOLI, FERNANDO; ROSSATO, JANINE; CAMMAROTA, MARTIN; MEDINA, JORGE H

Congreso; 8th FENS fórum of neuroscience 2012; 2012

In general, the hippocampus is seen as a sparse and fast learning structure which encodes an event using separated representations minimizing interference, whereas the neocortex is a distributed, overlapping and gradually integrating information structure with a low learning rate. Nevertheless, recent results provide evidence for alternative views which propose that the neocortex may have a crucial role from initial steps of memory formation. In this work, we aim to study how the hippocampus and the neocortex, specifically the dorso-medial prefrontal cortex (dmPFC), work together to support learning, permanent storage and retrieval of an aversive memory. We found that an inhibitory avoidance (IA) task in rats, an hippocampal-dependent learning, is associated with up-regulation of immediate early genes in dmPFC few hours after the learning session. Both pharmacological inactivation with muscimol or protein synthesis inhibition with emetine into that area prevent memory formation (infusion around training) and long term memory (LTM) persistence (infusions at 6, 9 or 12 hours after training). Infusion of muscimol into the dmPFC 15 minutes pre-test, also prevents the retrieval of the IA memory 2, 14, 28 and 42 days after the learning session. These results posit the dmPFC in a central role in memory processing at both early and late stages and challenge the standard theory confirming recent results demonstrating that systems memory consolidation can be very fast (Tse et al., Science; 2011).