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What the mouse´s eye tells the mouse`s brain

Tübingen neuroscientists study the information flow from the eye to the brain and show that the interpretation of images in the retina is more elaborate than previously thought.

Tübingen researchers have shown that image processing in the eye is even more extensive than previously thought. They investigated the channels that transmit information from the eye to the brain. In the course of this investigation, they not only identified numerous new cell types: they also found that the retina seems to possess around different channels into the brain, twice as many as previously assumed. The results of their study are published in the latest edition of Nature (DOI: 10.1038/nature16468)

“What the frog’s eye tells the frog’s brain“ was the title that cognition scientist Jerome Lettvin gave to a seminal paper he published in 1959. He was able to show that the eye does not simply take pictures like a camera, nor does it send them to the brain without filtering. Instead, the eye already extracts valuable information from the image. In the case of the frog, for example, it might ”tell” the brain: “There is something small and dark over there, possibly a fly“. At the time, Lettvin was ridiculed at conferences for his revolutionary hypotheses. More than half a century later, his heavily cited paper is considered a milestone in modern neuroscience. It raised questions that are still being pursued by scientists today.

A Tübingen-based team of researchers now tackled these questions anew, led by Prof. Thomas Euler and Prof. Matthias Bethge (Werner Reichardt Centre for Integrative Neuroscience, Bernstein Center for Computational Neuroscience, and Institute for Ophthalmic Research). The neuroscientists set out to survey what information the retina in its entirety transmits to the brain. To this end, they undertook a study of unusual scale, recording signals from more than 11,000 individual retinal cells in mice. For reference, the largest similar study to date was based on a sample of ~450 cells.

Drawing on state-of-the-art experimental and analytical tools, the researchers studied the so-called retinal ganglion cells (RGCs). They made use of electroporation, a staining technique which makes whole populations of nerve cells visible under the microscope, to watch individual cells at work in real-time. The vast amount of data was analysed using advanced machine learning algorithms. The scientists were particularly interested in the diverse functions of these cells: different types of ganglion cells respond to different properties of the visual scene and independently send this information to the brain. Each RGC, or each “information channel”, thereby informs the brain about specific image aspects such as colour, the presence of an edge or the direction of movement. From these information channels, the brain constantly re-assembles its own image-stream of our subjective visual world.

Based on their functional analysis, the scientists were able to identify up to 40 types of ganglion cells in the retina, very likely representing as many information channels. This is far more than the at most 20 types which had been previously assumed. While the results from the mouse model cannot be applied to humans in a 1:1 fashion, the retina is very similar in all mammals. Accordingly, an analogous classification in humans may now be within reach.

The large number of different information channels means that the retina does not simply transform received light signals into nerve cell signals. Instead, it also interprets the signals in fundamental ways. Their work in basic research has brought the Tübingen neuroscientists a large step closer to understanding how images may be interpreted in the brain. Since many diseases of the eye only affect certain retinal cell types, these insights may eventually help in developing more specific therapies. In Tübingen, research on prosthetic technology to restore sight to blind people (retina implants) has been going strong for many years. This research stands to profit massively from the new results: current models still stimulate the retina relatively non-specifically. New insights provided by the study at hand might help future versions to feed visual information into the appropriate channels.

Publication

Baden T, Berens P, Franke K, Román Rosón M, Bethge M, & Euler T (2016). The functional diversity of retinal ganglion cells in the mouse. Nature 10.1038/nature16468.

Contact

Professor Thomas Euler

University of Tübingen
Werner Reichardt Center for Integrative Neuroscience (CIN)

Phone +49 7071 29-85028
E-mail: thomas.euler[at]cin.uni-tuebingen.de
Website: www.eye-tuebingen.de/eulerlab

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