National Science Foundation     |     Directorate for Engineering  (ENG) Division of Chemical, Bioengineering, Environmental, & Transport Systems  (CBET)   CBET Award Achievements  (Formerly "CBET Nuggets") Notable Accomplishments from CBET Awards

Assessing and Optimizing Retinal Prosthetic Stimulation   Nicolas Cottaris  -  Wayne State University;  Detroit, MI

Devices that have the potential to stimulate the nerves attached to the retina in the back of the eye have become available to members of the blind community and have the potential to partially restore the sense of sight.  The NSF-funded project, led by Dr. Cottaris at Wayne State University, is improving the methods used to quantitatively evaluate the multi-dimensional space of electric stimulation of the retina.  Currently, methods have been developed to decode nerve activity as a result of retinal stimulation, thereby allowing for the computation of the information transmitted from the retina to the brain.  The proposed systematic approach to nerve stimulation in the eye has the potential to lead to the development of improved methods of activating the nerves, thereby, increasing the efficiency of the implant and, ultimately, the vision. Background:  NSF-funded researcher Cottaris and his team have developed a novel paradigm for assessing and optimizing the efficacy of retinal prosthetic stimulation based on neural feedback from the brain.  Presently, the perceptual efficacy of retinal prostheses is assessed in behavioral experiments with blind volunteers.  However, that approach is qualitative and prone to patient fatigue and frustration.  The paradigm pioneered by the Wayne State group allows for a more systematic exploration of the multi-dimensional space of electric stimulation of the retina and may lead to the development of improved stimulation methods.  Such methods are urgently needed as present retinal implants have not produced visual percepts beyond amorphous spots of light in blind patients. Results:  The approach developed by the Cottaris team employs large-scale recordings of neural activity from the primary visual cortex.  The primary visual cortex is the first area in the brain that processes the retinal output, and neurons in this area extract information about the shape of visual objects, such as their orientation (Figure 1a).  The team has developed analysis methods that decode the sampled cortical activity to identify the inducing retinal stimuli, thereby computing the information transmitted from the retina to the brain.  They demonstrated that several key spatial components of visual objects, including retinal location, orientation and spatial frequency content can be estimated accurately by decoding neural activity recorded at 80 sites within a small (2.5 x 4.0 mm) region of the cortex.   This method was used to measure transmission of information regarding stimulus orientation for electric stimuli delivered via an epiretinal 32-electrode retinal implant (Figure 1b).  The employed stimuli were multi-focal, oriented patterns (Figure 2a), that were delivered either synchronously, with the engaged electrodes all injecting current simultaneously, or asynchronously, with the engaged electrodes injecting current with slightly different latencies.  It was found that during synchronous current injection, stimuli of different orientations induced cortical response patterns that were strikingly similar to each other (Figure 2b1), indicating that the brain was not able to decode the orientation of different prosthetic stimuli.  On the other hand, during asynchronous current injection, stimuli of different orientations induced different cortical response patterns (Figure 2b2), and decoding of stimulus orientation was very accurate for a number of orientations.  This finding indicates that asynchronously delivered retinal prosthetic stimuli may have a strong potential for inducing spatially-patterned percepts.  The approach developed by the Cottaris team provides a systematic and powerful tool that can be used to assess and optimize the efficacy of different paradigms of retinal prosthetic stimulation, and ultimately lead to the development of spatial vision-capable retinal prostheses for the blind.

Figure 1a.  Visual receptive fields of orientation-processing primary visual cortex neurons

Figure 1b.  Retinal prosthesis (32-electrodes)

Figure 2a.  Retinal multi-focal stimulation patterns

Figure 2b1.  Cortical response (magnitude and phase) in response to retinal multi-focal stimulation - - synchronous current delivery

Figure 2b2.  Cortical response (magnitude and phase) in response to retinal multi-focal stimulation - - asynchronous current delivery.

Credit for All Images:  Nicolas P. Cottaris, Ph.D. Wayne State University

Scientific Uniqueness:  This work is unique in that it pioneers an innovative, objective and systematic method for assessing and optimizing the information transmitted by a retinal prosthesis to the brain.

This project addresses the NSF Strategic Outcome Goals, as described in the NSF Strategic Plan 2006-2011, as follows:   Primary Strategic Outcome Goal:      (1) Discovery:  This project provides a powerful tool to discover novel and efficacious methods of retinal prosthetic stimulation.                                                                      (1) Discovery Categories:                                                                            -  Biology                                                                            -  Engineering   Secondary Strategic Outcome Goal:  (2) Learning:  This project includes participation of a graduate student and a post-doctoral student from Engineering.                                                                      (2) Learning Categories:                                                                            -  Graduate Education and Graduate Student Research                                                                            -  Postdoctoral Education and Fellowships This Award Achievement represents Transformative Research.  The optimization of parameters of retinal prosthetic stimulation is guided by decoding brain responses, which is an objective criterion.  This approach may lead to the discovery of prosthetic stimulation parameters that have been missed in previous clinical trials.  Since the discovered parameter space would maximize the amount of spatial information transmitted to the cortex, it would likely also maximize the efficacy of a retinal implant to induce percepts beyond amorphous phosphenes. The Intellectual Merit of this research:  The approach taken in this work provides a powerful proxy to gauging the perceptual efficacy of any retinal prosthetic stimulation paradigm without relying on behavioral responses, which are qualitative and subject to patient fatigue and frustration. The Broader Impacts of this research include:   -  Benefits to Society:  The discovery of perceptually efficacious retinal prosthetic stimulation methods would enable partial restoration of spatial vision to patients affected by retinal degenerated diseases, such as retinitis pigmentosa and age-related macular degeneration, which affect 25 million people worldwide including 6 million in the U.S. Area of Emphasis (Themes) for FY 2010 Highlights included in this research project:   -  Interdisciplinary, high-risk, and potentially transformative

Program Director:		Ted Conway CBET Program Director - Research to Aid Persons with Disabilities
NSF Award Number:		0756098
Award Title:		Neurophysiologically-based computational platform for the characterization and optimization of retinal prosthetic stimulation
PI Name:		Nicolas Cottaris
Institution Name:		Wayne State University;  Detroit, MI
Program Element Code:		5342
CBET Award Achievement:		FY 2010

Top of Page This Award Achievement was Updated on 17 August 2010.