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Alexander Borst

Wednesday 25th November 2015

Time: 4.00pm

 

Ground Floor Seminar Room

25 Howland Street, London, W1T 4JG

 

Neural Circuits for Elementary Motion Detection

 

Alexander Borst, MPI Neurobiology, Martinsried, Germany

 

Visual motion information plays a key role in the life of most animals, signaling the presence of a mate, detecting the direction in which a prey or a predator is moving, as well as being fundamental for visual course control. Therefore, directionally selective neurons are commonly found in the visual system of almost all animals. In the fly visual system, the process by which directional information is extracted from the photoreceptor signals is well described by a mathematical model developed more than 50 years ago, the so-called ‘Hassenstein-Reichardt-Detector’. In this model, the luminance values derived from adjacent photoreceptors become multiplied after differential temporal filtering. This is done twice in a mirror-symmetrical way, and the output values of the multipliers are finally subtracted from each. However, the neurons performing the computations defined by this model have not been known for long. By silencing, activating and optically recording from genetically targeted candidate neurons in Drosophila, we found that (1) motion is processed in two parallel circuits specialized for brightness increments (ON-pathway) and decrements (OFF-pathway), respectively (Joesch et al, 2010, Nature 468: 300), (2) T4 and T5 cells are the first neurons in each pathway that respond to visual motion in a directionally selective way (T4 in the ON-, T5 in the OFF-pathway; Maisak et al, 2013, Nature 500: 212), and (3) that lobula plate intrinsic neurons implement the above mentioned subtraction (Mauss et al, 2015, Cell 162: 351). Our current work focuses on the role of the various input neurons to T4 and T5 cells and how they give rise to directional selectivity in the postsynaptic dendrites.

Alexander Borst:
Born 18th August 1957 in Bad Neustadt/S, Germany.
Studies of Biology, Universität Würzburg, Germany (1976-1980).
PhD with Martin Heisenberg, Universität Würzburg, Germany (1984).
Research Assistant, Max-Planck-Institute of Biological Cybernetics, Tübingen (1984-1993).
Junior Group Leader at the FML, Tübingen (1993-1999).
Professor at UC Berkeley (1999-2001).
Director, Max Planck Institute of Neurobiology, Martinsried (since 2001).