Large-scale multi-electrode recording from primate retina
Our approach to understanding retinal processing relies first and foremost on measuring the patterns of electrical activity induced by visual stimuli in large collections of retinal ganglion cells (RGCs) in primate retina. We measure the activity of RGCs using multi-electrode recordings from isolated primate retinas in vitro. We obtain primate retinas from animals used by other investigators in the course of their experiments.
To record the large-scale patterns of retinal activity responsible for visual sensation, we collaborated with the groups of physicists Alan Litke and Wladeck Dabrowski in the development of a unique 512-electrode electrophysiological recording system. We use the system to sample the activity of several hundred RGCs simultaneously. The photo below shows the circular recording chamber containing a nanofabricated 512-electrode array, custom analog VLSI electronics surrounding the chamber, and supporting electronics:
The movie below shows the recorded waves of neural activity sweeping across the retina in response to images of moving bars. This reveals how the ensemble of recorded RGCs encodes visual motion.
The above techniques makes possible a singularly clear view of how multiple classes of retinal ganglion cells represent the visual scene. In the figure below, the receptive fields of several hundred RGCs recorded from a peripheral region of primate retina are shown (center, top). These receptive fields cover a 4x8 degree region of the visual field. Examination of light response properties (center, bottom) reveals several distinct cell types. Each distinct cell type tiles the retina uniformly with minimal overlap (left, right). This indicates that each functionally identified cell type in our recordings corresponds to a morphologically distinct cell type in the retina, projecting to a distinct target in the brain. The most commonly sampled cell types are the so-called parasol and midget cells, which provide the highest spatial resolution image to the brain.
The nearly complete mosaics indicate that we have recorded nearly all the ON and OFF parasol cells over this region of retina. Thus, our approach allows us to study the ensemble activity in complete populations of cells of a known type, with known central projections, in the primate visual system.
Technology Development Personnel (past and present)
Electrode Array and Acquisition System Development: Alan Litke, Sergei Kachiguin, Matthew Grivich, Alexander Sher, Dumitru Petrusca, Alex Grillo, Gary Taylor, Bill Rowe, Tim Dubbs (University of California, Santa Cruz), Keith Mathieson, Debbie Gunning (University of Glasgow).
Neurochip Development: Wladeck Dabrowski, Pawel Grybos, Andrzej Skoczen, Pawel Hottowy (AGH University of Science and Technology, Krakow).
Neurobiology: E.J. Chichilnisky, Rachel Kalmar, Eric Frechette (Salk Institute)
Technical Support: Steve Barry, Jessica French (Salk Institute)