With the accumulation of our knowledge about how memories are formed, consolidated, retrieved, and updated, neuroscience is now reaching a point where discrete memories can be identified and manipulated at rapid timescales. Here, we start with historical studies that lead to the modern memory engram theory. Then, we will review recent advances in memory engram research that combine transgenic and optogenetic approaches to reveal the underlying neuronal substrates sufficient for activating mnemonic processes. We will focus on three concepts: (1) isolating memory engrams at the level of single cells to tag them for subsequent manipulation; (2) testing the sufficiency of these engrams for memory recall by artificially activating them; and (3) presenting new stimuli during the artificial activation of these engrams to induce an association between the two to form a false memory. We propose that hippocampal cells that show activity-dependent changes during learning construct a cellular basis for contextual memory engrams.
Keywords: optogenetics, memory engram, IEG, ChR2, false memory
Citation: Ramirez S, Tonegawa S and Liu X (2014) Identification and optogenetic manipulation of memory engrams in the hippocampus. Front. Behav. Neurosci. 7:226. doi: 10.3389/fnbeh.2013.00226
Received: 22 November 2013; Paper pending published: 06 December 2013;
Accepted: 27 December 2013; Published online: 17 January 2014.
Edited by:Anton Ilango, National Institutes of Health, USA
Reviewed by:Mazahir T. Hasan, Charité-Universitätsmedizin, Germany
Copyright © 2014 Ramirez, Tonegawa and Liu. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
*Correspondence: Xu Liu, Department of Biology and Department of Brain and Cognitive Sciences, RIKEN-MIT Center for Neural Circuit Genetics at the Picower Institute for Learning and Memory and Howard Hughes Medical Institute, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Building 46-5261, Cambridge, MA 02139, USA e-mail: email@example.com