Biomedical Engineering Reference
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1
Microstimulation with Chronically
Implanted Intracortical Electrodes
Douglas McCreery
Neural Engineering Program
Huntington Medical Research Institutes
Abstract:
Stimulating microelectrodes that penetrate into the brain afford a means of
accessing the basic functional units of the central nervous system. Micros-
timulation in the region of the cerebral cortex that subserve vision may be
an alternative, or an adjunct, to a retinal prosthesis, and may be particularly
attractive as a means of restoring a semblance of high-resolution central
vision. There also is the intriguing possibility that such a prosthesis could
convey higher order visual percepts, many of which are mediated by neural
circuits in the secondary or “extra-striate” visual areas that surround the
primary visual cortex. The technologies of intracortical stimulating micro-
electrodes and investigations of the effects of microstimulation on neural
tissue have advanced to the point where a cortical-level prosthesis is at
least feasible. The imperative of protecting neural tissue from stimulation-
induced damage imposes constraints on the selection of stimulus parameters,
as does the requirement that the stimulation not greatly affect the electrical
excitability of the neurons that are to be activated. The latter is especially
likely to occur when many adjacent microelectrodes are pulsed, as will be
necessary in a visual prosthesis. However, data from animal studies indicates
that these restrictions on stimulus parameter are compatible with those that
can evoke visual percepts in humans and in experimental animals. These
findings give cause to be optimistic about the prospects for realizing a visual
prosthesis utilizing intracortical microstimulation.
Introduction
The feasibility of a visual prosthesis to restore vision to a blind person using
intracortical microstimulation (ICMS) in the visual cortex was first studied in
a 42-year-old woman who had been totally blind for 22 years secondary to
glaucoma [1]. Thirty-eight microelectrodes were implanted in the right visual
cortex, near the occipital pole, for a period of 4 months. Visual percepts reported
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