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Neural Plasticity
Volume 2011, Article ID 203462, 11 pages
Review Article

Reactivation, Replay, and Preplay: How It Might All Fit Together

Laure Buhry,1,2 Amir H. Azizi,1,2,3 and Sen Cheng1,2,3

1Mercator Research Group “Structure of Memory”, Ruhr-University Bochum, Universitaetsstraße 150, 44801 Bochum, Germany
2Faculty of Psychology, Ruhr-University Bochum, Universitaetsstraße 150, 44801 Bochum, Germany
3International Graduate School of Neuroscience, Ruhr-University Bochum, Universitaetsstraße 150, 44801 Bochum, Germany

Received 7 April 2011; Revised 13 June 2011; Accepted 15 June 2011

Academic Editor: Christian Leibold

Copyright © 2011 Laure Buhry et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Sequential activation of neurons that occurs during “offline” states, such as sleep or awake rest, is correlated with neural sequences recorded during preceding exploration phases. This so-called reactivation, or replay, has been observed in a number of different brain regions such as the striatum, prefrontal cortex, primary visual cortex and, most prominently, the hippocampus. Reactivation largely co-occurs together with hippocampal sharp-waves/ripples, brief high-frequency bursts in the local field potential. Here, we first review the mounting evidence for the hypothesis that reactivation is the neural mechanism for memory consolidation during sleep. We then discuss recent results that suggest that offline sequential activity in the waking state might not be simple repetitions of previously experienced sequences. Some offline sequential activity occurs before animals are exposed to a novel environment for the first time, and some sequences activated offline correspond to trajectories never experienced by the animal. We propose a conceptual framework for the dynamics of offline sequential activity that can parsimoniously describe a broad spectrum of experimental results. These results point to a potentially broader role of offline sequential activity in cognitive functions such as maintenance of spatial representation, learning, or planning.