Reverse engineering the brain: A hippocampal cognitive prosthesis for repair and enhancement of memory function

This chapter provides an update, including some of the most recent experimental and theoretical studies describing the development of a cognitive prosthesis designed to restore the ability to form new long-term memories—a memory capability lost after damage to the hippocampal formation and surrounding temporal lobe brain structures. This chapter also will describe recent studies demonstrating that the same device and procedures used to restore lost hippocampal memory function also can be used to enhance memory capability in otherwise normal animals. The animal model used in studying the loss and recovery of hippocampal memory is delayed nonmatch-to-sample (DNMS) behavior in the rat. The “core” of the prosthesis is a biomimetic multi-input/multi-output (MIMO) nonlinear model that provides the capability for predicting spatio-temporal spike train output of hippocampus (CA1) based on spatio-temporal spike train inputs recorded presynaptically to CA1 (e.g., CA3). We demonstrate the capability of the MIMO model for highly accurate predictions of CA1-coded memories that can be made on a single-trial basis and in real time. When hippocampal CA1 function is blocked and long-term memory formation is lost, successful DNMS behavior also is abolished. However, when MIMO model predictions are used to reinstate CA1 memory-related activity by driving spatio-temporal electrical stimulation of hippocampal output to mimic the patterns of activity observed in control conditions, successful DNMS behavior is restored. We also outline the design in VLSI for a hardware implementation of a 16-input, 16-output MIMO model, along with spike sorting, amplification, and other functions necessary for a comprehensive system, when coupled together with electrode arrays to record extracellularly from populations of hippocampal neurons, that can serve as a cognitive prosthesis in behaving animals.