Special CNS Seminar

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 finally are subtracted from each. However, the neurons performing the computations defined by this model have not been known for long. By silencing and optical recording from genetically targeted candidate neurons in Drosophila, we recently identified the input and output neurons of two parallel circuits specialized to process the motion of brightness increments (ON-pathway) and brightness decrements (OFF-pathway), respectively. Current work aims at completing the circuit by testing the participation and characterizing the response properties of various interneurons suggested by anatomy.