Neurobiologists characterize nerve cells that detect motion by light changes
The ability to see the direction in which something is moving is vital for survival. Only in this way is it possible to avoid predators, capture prey or, as humans in a modern world, cross a road safely. However, the direction of motion is not explicitly represented at the level of the photoreceptors but rather must be calculated by subsequent layers of nerve cells.
Scientists from the Max Planck Institute of Neurobiology in Martinsried have now discovered that, in fruit flies, four classes of nerve cell are involved in calculating directionally selective signals. This is strikingly different from mathematical models of motion detection discussed in the literature so far.
When crossing a road, it’s advantageous to know the direction in which nearby cars are moving. However, the individual light sensitive cells in the eye only signal local changes in brightness, whether an image point becomes brighter or darker. The direction of motion is detected in a downstream neuronal network.
Alexander Borst and his team at the Max Planck Institute of Neurobiology have unravelled cell by cell how the brain calculates motion from light changes. Their model is the fruit fly, a master in motion vision, possessing a relatively small brain.
Although there are more than 50,000 nerve cells in the area of the fruit fly brain responsible for motion vision, the researchers believe that the network is “simple” enough to allow them to understand the circuitry at the cellular level. In previous studies, they have shown that in flies, similar to vertebrates, motion is detected in two parallel pathways, one for moving bright edges (ON-pathway) and one for moving dark edges (OFF-pathway).
The scientists have now succeeded in identifying the first nerve cells in the fruit flies’ OFF-pathway, known as T5 cells, which perceive the direction of motion. These cells receive input from four upstream cells, called Tm cells. A whole series of experiments based on two-photon microscopy, electrophysiology and behavioural analyses have shown that Tm cells are activated specifically by “light OFF” brightness changes. In contrast, T5 cells are only activated by motion of OFF-edges in a specific direction.
The signals of all four Tm cells are required for a directionally selective signal to arise in a T5 cell. “That was a surprising finding, because mathematical models for motion detection only involved two input cells,” reports Etienne Serbe, one of the two lead authors of the study. “Another exciting finding is that the visual system of vertebrates deviates from these models in a similar way,” says Matthias Meier, the other lead author.
Alexander Borst and a colleague have recently demonstrated the many common features in the visual circuits of flies and mice (review article in Nature Neuroscience). “This recently discovered commonality also shows that we can gain fundamental insights into the circuitry of the brain from investigations of the fly”, says Alexander Borst. “I’m already curious about what we will discover next in the motion circuit.”
Dr. Stefanie Merker
Max Planck Institute of Neurobiology, Martinsried
Phone: +49 89 8578-3514
Prof. Dr. Alexander Borst
Max Planck Institute of Neurobiology, Martinsried
Phone: +49 89 8578-3251
Fax: +49 89 8578-3252
Etienne Serbe, Matthias Meier, Aljoscha Leonhardt und Alexander Borst
Comprehensive characterization of the major presynaptic elements to the Drosophila OFF motion detector.
Neuron; 4 February, 2016
Dr. Stefanie Merker | Max Planck Institute of Neurobiology, Martinsried
World’s Largest Study on Allergic Rhinitis Reveals new Risk Genes
17.07.2018 | Helmholtz Zentrum München - Deutsches Forschungszentrum für Gesundheit und Umwelt
Plant mothers talk to their embryos via the hormone auxin
17.07.2018 | Institute of Science and Technology Austria
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.
Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...
13.07.2018 | Event News
12.07.2018 | Event News
03.07.2018 | Event News
17.07.2018 | Information Technology
17.07.2018 | Materials Sciences
17.07.2018 | Power and Electrical Engineering