Optimizing Stimulation Strategies for Cortical Visual Prostheses
Abstract
Blast injuries have become increasingly common in military conflict, leading to a large number of Warfighters who suffer eye trauma and subsequent lifelong vision loss. Cortical visual prostheses have the potential to restore sight to these individuals as well as to those with other forms of irreparable eye damage. The principle behind these devices is that stimulating neurons in the visual center of the brain causes a blind person to see light. Furthermore, the pattern of light corresponds to the pattern of stimulated neurons. Therefore, for example, stimulating a straight line of neurons in the brain would cause the person to see a straight line. To investigate the feasibility of a cortical visual prosthesis, scientists have implanted microchips into the brains of blind humans. Each chip contained tens of tiny electrodes arranged in a grid. To cause the patient to see a pattern of light such as the letter "L," the scientists delivered electrical current through a group of electrodes arranged in the shape of that letter, with the goal of stimulating an L-shaped pattern of neurons. They discovered, however, that patients often had trouble recognizing letters and other simple shapes. The likely reason for this was revealed by recent animal studies: It is not possible to precisely control the patterns of neurons in the brain that are stimulated by electrodes. While each electrode is supposed to stimulate just a few neurons in its immediate vicinity, an electrode implanted in the brain will actually stimulate a seemingly random pattern of neurons, many of which are located far away. This presents a critical problem for the development of a cortical visual prosthesis: The inability to stimulate precise patterns of neurons in the visual center of the brain makes it impossible to accurately control the patterns of light seen by the patient. In the proposed research project, our goal is to identify electrical stimulation strategies that enable precise control over the patterns of stimulated neurons in the brain. To do this, we will leverage a novel imaging technology that we developed, one that allows us to visualize under the microscope the patterns of neurons in animal tissue that are excited by electrical stimulation. We have previously used this technique in the retina to improve electrical stimulation strategies for retinal visual prostheses. We now propose to apply our technique in the visual center of the brains of rats. We will label neurons in the visual center with a special fluorescent molecule that lights up when the neurons are stimulated, enabling us to determine exactly what pattern of activity the electrical stimulation causes in the brain cells. While imaging the brain under the microscope, we will test a number of different electrical stimuli with the goal of finding one that enables precise control over the patterns of stimulated neurons. We expect our work will result in novel electrical stimulation strategies that allow precise control over the patterns of light seen by cortical visual prosthesis patients. This has the potential to enable patients to read large print as well as identify faces and objects critical to daily life. Results from our study will directly inform the engineering design of a prototype cortical visual prosthesis. Specifically, we will better understand how to design microchips that are implanted in the brain as well as the hardware that controls stimulation of the microchips electrodes. As such, our proposed research directly addresses the following Vision Prosthesis Pilot Study Award Focus Area: "Studies to demonstrate the efficacy of novel cortical stimulation methodologies (stimulation of non-visual cortex is acceptable for demonstration)."
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jan 31, 2017
- Source ID
- W81XWH1620024
Entities
People
- Andrew Weitz
Organizations
- United States Army
- University of Southern California