U.S. medical researchers John S. Pezaris and R. Clay Reid at the Department of Neurobiology in Boston, Massachusetts’ Harvard Medical School are studying electrical stimulation of the visual system so that in the future a prosthetic device could be used to restore sight in blind people.

Their paper “Demonstration of artificial visual percepts generated through thalamic microstimulation” is published in the journal Proceedings of the National Academy of Sciences (online April 23, and in print on May 1, 2007).

Within the paper, Pezaris and Reid talk about performing microstimulation on the dorsal lateral geniculate nucleus of the thalamus of macaques (short-tailed monkeys). The lateral geniculate nucleus is the region of the thalamus that sends visual signals from the retina to the cerebral cortex. The thalamus is a pair of egg-shaped masses of matter located beneath each cerebral hemisphere of the brain.

Current visual prosthetics use implants located behind the retina. These prosthetics stimulate nerve cells (retinal neurons) in order to generate visual sensations. However, only a partial map has been completed that would allow sight to be restored. In addition, sufficient numbers of nerve cells are not always available to restore vision after serious eye damage has occurred.

The work of Pezaris and Reid has already showed that monkeys can be told where to look when their nerve cells are stimulated with the use of implanted electrodes in their thalamus. Such implants in humans may lead to the building of bionic eyes to restore vision.

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