Brain Implantable Biomimetic Electronics as the Next Era in Neural Prosthetics

An interdisciplinary multilaboratory effort to develop an implantable neural prosthetic that can coexist and bidirectionally communicate with living brain tissue is described. Although the final achievement of such a goal is many years in the future, it is proposed that the path to an implantable prosthetic is now definable, allowing the problem to be solved in a rational, incremental manner. Outlined in this report is our collective progress in developing the underlying science and technology that will enable the functions of specific brain damaged regions to be replaced by multichip modules consisting of novel hybrid analog/digital microchips. The component microchips are “neurocomputational” incorporating experimentally based mathematical models of the nonlinear dynamic and adaptive properties of biological neurons and neural networks. The hardware developed to date, although limited in capacity, can perform computations supporting cognitive functions such as pattern recognition, but more generally will support any brain function for which there is sufficient experimental information. To allow the “neurocomputational” multichip module to communicate with existing brain tissue, another novel microcircuitry element has been developed—silicon-based multielectrode arrays that are “neuromorphic,” i.e., designed to conform to the region-specific cytoarchitecture of the brain. When the “neurocomputational” and “neuromorphic” components are fully integrated, our vision is that the resulting prosthetic, after intracranial implantation, will receive electrical impulses from targeted subregions of the brain, process the information using the hardware model of that brain region, and communicate back to the functioning brain. The proposed prosthetic microchips also have been designed with parameters that can be optimized after implantation, allowing each prosthetic to adapt to a particular user/patient.
One of the true frontiers in the biomedical sciences is repair of the human brain: developing prosthetics for the central nervous system to replace higher thought processes that have been lost due to damage or disease. The type of neural prosthetic that performs or assists a cognitive function is qualitatively different than the cochlear implant or artificial retina, which transduce physical energy from the environment into electrical stimulation of nerve fibers and qualitatively different than functional electrical stimulation (FES), in which preprogrammed electrical stimulation protocols are used to activate muscular movement . Instead, we consider here a neural prosthetic designed to replace damaged neurons in central regions of the brain with silicon neurons that are permanently implanted into the damaged region. The replacement silicon neurons would have functional properties specific to those of the damaged neurons, and would both receive as inputs and send as outputs electrical activity to regions of the brain with which the damaged region previously communicated.

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