Retina works like a multi-layered jigsaw puzzle of receptive fields

WASHINGTON - Scientists at the Salk Institute for Biological Studies have found that the retina works like a multi-layered jigsaw puzzle of jagged windows called receptive fields, through which about 1.25 million neurons view the world.

The researchers have revealed that these receptive fields fit together like pieces of a puzzle, preventing "blind spots" and excessive overlap that could blur our perception of the world.

They say that their findings suggest that the nervous system operates with higher precision than previously appreciated, and that apparent irregularities in individual cells may actually be coordinated and finely tuned to make the most of the world around us.

The irregularities of individual receptive fields observed previously suggested that the collective visual coverage might be uneven and irregular, potentially posing a problem for high-resolution vision.

"The striking coordination we found when we examined a whole population indicated that neuronal circuits in the retina may sample the visual scene with high precision, perhaps in a manner that approaches the optimum for high-resolution vision," says senior author Dr. E.J. Chichilnisky, an associate professor in the Systems Neurobiology Laboratories.

The researchers point out that all visual information reaching the brain is transmitted by retinal ganglion cells.

They say that each of the 20 or so distinct ganglion cell types is thought to transmit a complete visual image to the brain, because the receptive fields of each type form a regular lattice covering visual space.

They, however, add that within each regular lattice, the individual cells' receptive fields have irregular and inconsistent shapes, which could potentially result in patchy coverage of the visual field.

Dr. Jeffrey L. Gauthier, the first author of the study, wanted to understand how the visual system overcomes this problem.

He used a microscopic electrode array to record the activity of ganglion cells in isolated patches of retina, the tissue lining the back of the eye.

The researcher monitored hundreds of ganglion cells over several hours, and then distinguished between different cell types based on their light response properties.

"Often people record from many cells simultaneously but they don't know which cell belongs to which type," says Gauthier.

He says that it was this information due to which he could observe that the receptive fields of neighbouring cells of a specific type interlock, complementing each others' irregular shapes.

"The receptive fields of all four cell types we examined were precisely coordinated, but we saw no coordination between cells of different types, emphasizing the importance of clearly distinguishing one cell type from another when studying sensory encoding by a population of neurons," he says.

The study has been published in the journal Public Library of Science, Biology. (ANI)


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