Hippocampal Prosthesis

The hippocampus is responsible for the formation of new long-term declarative memories: the formation of mnemonic labels that identify a collection of features and form relations between multiple collections of features. It is the degeneration and malformation of hippocampal neurons that causes the memory disorders associated with stroke, epilepsy, dementia, and Alzheimer’s.

A hippocampal memory prosthesis is a Brain Machine Interface device developed for restoring or enhancing memory functions. It is designed to circumvent damaged hippocampal tissue by re-establishing the ensemble coding of spike trains performed by a normal population of hippocampal neurons. The objective is to restore long-term memory function in a stimulus-specific manner using a multi-input, multi-output (MIMO) nonlinear dynamical model. 

The prosthesis is a multi-circuit, biomimetic system that consists of three components: (1) a multi-electrode array for recording the ensemble spike trains from an upstream hippocampal region, e.g., CA3, (2) a VLSI chip with a MIMO nonlinear dynamical model for predicting the output (e.g., CA1) ensemble spike trains based on the ongoing input (e.g., CA3) ensemble spike trains, and (3) an electrical stimulator for stimulating the downstream hippocampal region, e.g., CA1, with the predicted output spatio-temporal patterns of spikes.

For the first time, this microelectronic system does not just electrically stimulate cells to generally heighten or lower their average firing rates. Instead, the prosthesis incorporates mathematical models that replicate the fine-tuned, spatio-temporal coding of information by the hippocampal memory system, thus allowing memories for specific items or events experienced to be formed and stored in the brain.