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In humans, the visual system collects up to 80% of all the sensory data received from the environment. In order to make sense of this deluge of optical information, the visual inputs that are picked up and converted into electrochemical signals by the approximately 130 million light-sensitive cells in the retina are fed into, and processed by a complex network of nerve cells in the brain. How the brain manages to accomplish this task is still not fully understood. A more detailed picture of the steps involved is, however, essential for the further development of artificial visual systems. Now a team led by Ludwig-Maximilians-Universitaet (LMU) in Munich neurobiologist Laura Busse, in cooperation with Thomas Euler and Philipp Berens (University) has succeeded in shedding new light on a longstanding and controversial issue in this field. In an article that appears in the leading journal Neuron, the researchers demonstrate that incoming signals from the retina are subjected to selective processing and weighting at the first neuronal waystation in the functional pathway that connects the retina to the visual cortex.
In the mouse, the visual image that impinges on the retina is received by more than 30 specialized and functionally distinct types of ganglion cells. These different cell types respond in different ways to the input from the photoreceptors. For example, some react selectively to dark contrasts, while others are sensitive to particular spatial patterns. The streams of information that emanate from this retinal processing step are then conveyed in several parallel channels to the brain. "Primates appear to possess a similarly diverse set of retinal ganglion cells, and this most probably holds true for humans as well," says Busse. "Using the mouse as a model system, we have asked which types of ganglion cells project into the visual thalamus, and whether the information...
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