Thalamic Visual Prosthesis Project
The lateral geniculate nucleus of the thalamus (LGN) is a well-studied structure in the early visual pathway that links the retina to the primary visual cortex. As a deep structure, it has been long overlooked by the visual prosthesis field due to surgica
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Thalamic Visual Prosthesis Project Margee J. Kyada, Nathaniel J. Killian, and John S. Pezaris
Abstract The lateral geniculate nucleus of the thalamus (LGN) is a well-studied structure in the early visual pathway that links the retina to the primary visual cortex. As a deep structure, it has been long overlooked by the visual prosthesis field due to surgical inaccessibility. The unrelated field of deep brain stimulation has developed safe and effective means for clinical implantation of stimulating electrodes in structures that are near the LGN, removing the primary barrier for consideration of the thalamus as a stimulation target for artificial vision. In this chapter we review current progress toward creation of a thalamic visual prosthesis, describing initial animal experiments as proof-of-concept with single microwire electrodes, computer simulations of electrode placement and the resulting pattern of phosphenes in the visual field, experiments with sighted human volunteers to assess effective acuity of artificial vision using virtual reality simulations, and finally results from training animals in an artificial vision simulation in preparation for implantation of stimulating electrodes. Keywords Artificial vision • LGN • Microstimulation • Phosphene • Visual function • Blindness
Abbreviations CT DBS LGN logMAR MNREAD MRI V1
Computerized Tomography (X-ray) Deep Brain Stimulation Lateral Geniculate Nucleus logarithm of the minimum angle of resolution Minnesota Reading Test of Visual Acuity Magnetic Resonance Imaging Primary Visual Cortex
M.J. Kyada Department of Behavioral Neuroscience, Northeastern University, Boston, MA, USA N.J. Killian • J.S. Pezaris (*) Department of Neurosurgery, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA e-mail: [email protected]; [email protected] © Springer International Publishing Switzerland 2017 V.P. Gabel (ed.), Artificial Vision, DOI 10.1007/978-3-319-41876-6_14
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Key Points • The field of Deep Brain Stimulation has made placement of stimulating electrodes in midbrain structures routine, creating the possibility of easily implanting stimulating electrodes in LGN. • In monkeys, stimulation through microwires in LGN evokes phosphenes that are readily incorporated into a simple behavioral task. • In normally sighted humans, a virtual reality simulation of thalamic artificial vision showed that about 500 phosphenes total will provide reasonably useful vision, both with a letter recognition task, and a reading task. More phosphenes provide better performance. • The same virtual reality simulation showed that monkeys perform at levels comparable to humans in a letter recognition task in the easiest conditions, but somewhat worse in harder conditions, and only after significant training. • Current work involves development of a prototype device with 64-contact electrodes implanted bilaterally (128 contacts total) in monkeys.
Introduction Millions of people worldwide are at risk for complete vision loss [1]. There has
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