In the DARPA-led project REMIND, Prof. Ted Berger from the University of Southern California and Prof. Samuel Deadwyler from Wake Forest University have been developing an innovative type of neural prosthetic device for restoring and enhancing the formation of long-term memories. Their strategy is to build a computational model of the information processing in the hippocampus and use it as a substitute for normal memory encoding in people with brain trauma, dementia, stroke, and other disorders affecting learning. In their new work, the scientists have described achieving an important milestone – improving the memory formation in laboratory rats. In the performed behavioral tests, the rats were trained to remember the lever location and, after being distracted, had to recollect which lever to push. Two 16-electrode devices were implanted bilaterally for recording communication between the CA3 and CA1 sub-regions of the hippocampus. After the CA3 neuronal activity was recorded during successful recollection of the lever location, it was played back during the next recollection trial by stimulating the neurons at the CA1. And the rats displayed an amazing 20% improvement in their memory recollection (see the figure). Then, the scientists did something even more remarkable. They temporarily blocked the intrinsic CA1 activity (using a glutamate receptor antagonist), fully substituting it by the electrical stimulation. And the animals were able to remember the lever location equally well or even better than with their natural CA1 processing! These findings generate a lot of excitement, but the scientists are still facing a long road ahead to develop a fully functional replacement for hippocampus. One major challenge would be to build a scaled-up device for recording the activity of thousands of neurons in the hippocampus. Another hurdle, perhaps even more significant, would be to create a memory encoder that can go beyond replaying the previously-remembered tasks and to create brand new memories. After all, learning something new is a lot more exciting than, say, reciting the Pythagorean theorem for the N-th time.