Last Retinal Movement-Detecting Cell Discovered

In collaboration between high-energy physicists from the University of California in Santa Cruz, and neuroscientists from the Salk Institute in La Jolla, California, a ganglion cell in the retina of primates was found to react to movement. The cell was named Upsilon and is similar to Y cells in cats. Using a new dense electrode array, scientists were able to measure the activity of several upsilon cells simultaneously, and achieved a novel understanding of how these cells detect movement. This finding ends four decades of search for the movement-detecting cells in the retina.
Professor Alan Litke (Credit: UCSC) 
Professor Alan Litke
(Credit: UCSC)

The retina is composed of a set of neurons responsible for detecting the light  entering the eye, performing an initial processing of that signal, and sending it to the brain through the optic fibers. Light initially hits the rods and cones, and is then translated into a neural signal. The signal proceeds through three other layers of neurons until it reaches the ganglion. Biologists know of 22 different types of ganglion cells. However, the function of only a quarter of these cells is known, meaning that we do not know what the function of most of the ganglion cells is.  Understanding this preliminary stage in the signal transduction in the eye can tell us a lot about the overall light signal processing mechanism. 

In the past, electrodes were randomly injected into a preparation of a retina, measuring neuronal activity in some random cells while a movie was played. Because the upsilon cells are rare, simultaneously taking readings from several such cells using the above method was not likely to be successful. 

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The American scientists developed a new detection system, inspired by work that aimed to detect particles’ collisions in high-energy-physics.

  A pinhead-size 512-electrode array in the center of this
A pinhead-size 512-electrode array
in the center of this “neuroboard” records
the output of retinal neurons
(Credit: UCSC/A. Litke)

The new system includes 512 electrodes on a surface of 1.7 square millimeters. Using this new device, a reading of 250 cells was performed simultaneously, 10 of which were recognized as upsilon cells. While a movie of an oscillating pattern was shown to the preparation, significant activity was measured among the upsilon cells. 

The array of 512 electrodes enabled the team to further research other types of ganglion cells. The scientists say the upsilon cells are just the tip of the iceberg. Using this innovative technology a lot can be learned about the structure and function of the human eye, helping researchers gain new insight into human vision. This improved understanding of the eye may result in new therapeutic methods as well as in  future improvement in machine vision. 

More information can be found in the UCSC news release.