Hippocampal memory prosthesis

A hippocampal memory prosthesis is an implanted system that restores the hippocampus's memory-encoding function by electrically writing the output spike pattern that a healthy hippocampus would have produced. Rather than stimulating uniformly, it records the input activity arriving at region CA3, passes it through a patient-specific nonlinear model of the CA3-to-CA1 transformation, and delivers the predicted CA1 output pattern through the same electrodes — in effect bypassing damaged internal circuitry. The concept was developed principally by Theodore Berger's group with Sam Deadwyler and Robert Hampson, first in rodents and non-human primates, then in human epilepsy patients implanted with depth electrodes for seizure monitoring, largely under the DARPA Restoring Active Memory program.

Human demonstrations have reported facilitation of short-term and working memory when model-based stimulation is applied during encoding, with the largest gains in patients whose baseline memory was poorest. These are important proofs of principle, but they come from small cohorts of epilepsy patients performing constrained laboratory tasks, using electrodes placed for clinical rather than prosthetic reasons; generalization to a dedicated device, to declarative memory in daily life, and to non-epileptic patients remains unproven.