To build a cognitive prosthesis that can replace the memory function of the hippocampus, it is essential to model the input-output function of the damaged hippocampal region, so the prosthetic device can stimulate the downstream hippocampal region, e.g., CA1, with the output signal, e.g., CA1 spike trains, predicted from the ongoing input signal, e.g., CA3 spike trains, and the identified input-output function, e.g., CA3-CA1 model. In order for the downstream region to form appropriate long-term memories based on the restored output signal, furthermore, the output signal should contain sufficient information about the memories that the animal has formed. In this study, we verify this premise by applying regression and classification modelings of the spatio-temporal patterns of spike trains to the hippocampal CA3 and CA1 data recorded from rats performing a memory-dependent delayed non-match-to-sample (DNMS) task. The regression model is essentially the multiple-input, multiple-output (MIMO) non-linear dynamical model of spike train transformation. It predicts the output spike trains based on the input spike trains and thus restores the output signal. In addition, the classification model interprets the signal by relating the spatio-temporal patterns to the memory events. We have found that: (1) both hippocampal CA3 and CA1 spike trains contain sufficient information for predicting the locations of the sample responses (i.e., left and right memories) during the DNMS task; and more importantly (2) the CA1 spike trains predicted from the CA3 spike trains by the MIMO model also are sufficient for predicting the locations on a single-trial basis. These results show quantitatively that, with a moderate number of unitary recordings from the hippocampus, the MIMO non-linear dynamical model is able to extract and restore spatial memory information for the formation of long-term memories and thus can serve as the computational basis of the hippocampal memory prosthesis.
Keywords: hippocampus, spatio-temporal pattern, spike, classification, regression, memory
Citation: Song D, Harway M, Marmarelis VZ, Hampson RE, Deadwyler SA and Berger TW (2014) Extraction and restoration of hippocampal spatial memories with non-linear dynamical modeling. Front. Syst. Neurosci. 8:97. doi: 10.3389/fnsys.2014.00097
Received: 26 February 2014; Accepted: 06 May 2014;
Published online: 28 May 2014.
Edited by:Mikhail Lebedev, Duke University, USA
Reviewed by:Mikhail Lebedev, Duke University, USA
Copyright © 2014 Song, Harway, Marmarelis, Hampson, Deadwyler and Berger. 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: Dong Song, Department of Biomedical Engineering, University of Southern California, 403 Hedco Neuroscience Building, Los Angeles, CA 90089, USA e-mail: firstname.lastname@example.org