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Forschungsarbeit

Dynamic Receptive Fields of Motion-Sensitive Neurons in the Fly

by Franz Weber (20.11.2009)

Animals navigate with ease through their three-dimensional environment without losing their balance or colliding all the time with objects. To solve this complex task, primates (including ourselves) and flies heavily rely on vision.

When we move through the world, we see a specific pattern  of motions: E.g. when we move forward, objects on the left and right side seem to move backward. Or when we rotate around our body axis in a room, all objects are perceived to rotate in the opposite direction. More generally, each self-motion elicits a specific pattern of visually perceived motions, termed optic flow. Therefore, optic flow contains information about how we move through the surrounding environment. If a fly starts to drift laterally due to a sudden wind gust, the corresponding optic flow pattern allows the fly to visually perceive this unwanted drift.

optic flow of a fly when flying forward[Bildunterschrift / Subline]: (1) Self-motion elicits a specific pattern of visually perceived local motions, termed optic flow. When flying forward, the fly sees the surrounding environment moving backwards. The direction of the perceived local motions is indicated by the arrows.

In the fly brain, the so-called lobula plate contains about 60 motion-sensitive neurons that are sensitive to such optic flow patterns. In my master thesis, I studied how these neurons process complex stimuli: I presented motion stimuli to the fly on a screen, while recording the activity of a single neuron. Then, I developed a  theoretical model for the recorded neuron that allows to predict the neuron's response to a motion stimulus. This model was termed 'dynamic receptive field', since it comprises a spatial and temporal component: The spatial component or receptive field describes at which position in space the neuron 'wants to see' which motion direction. The temporal component gives insight in temporal aspects of motion processing; e.g. it indicates the reaction time of the neuron. Hence, although it is just a model, the dynamic receptive field gives a functional description of the investigated neuron. It therefore allows addressing the important question, what information is encoded by the neuron. Thus, it constitutes a link between the outside world and the activity of a neuron.

(2) The receptive field of the motion-sensitive neuron H1 located in the lobula plate of the fly.[Bildunterschrift / Subline]: (2) The receptive field of the motion-sensitive neuron H1 located in the lobula plate of the fly. This neuron is excited by a sidewards slip. The azimuth refers to a position along the horizontal in the visual space: 0 deg. is directly in front of the fly, -180 is behind the fly. Negative values correspond to positions on the left of the fly. The elevation angle denotes the location along the vertical: 0 deg. is again directly in front of the fly, whereas positive angles refer to locations above the fly. The direction of a single arrow denotes the motion direction that most strongly excites the neuron at the corresponding location. The length of the arrow shows how strongly the neuron is excited. Generally, the neuron H1 is excited by left-to-right motion on the left side of the fly. E.g. if a gust of wind drifts the fly to the left, H1 becomes active and, thus, signals this side drift.

Franz Weber
Franz Weber
* 1982, Bad Reichenhall

Education
  • 2003-2006
  • Bachelor in Bioinformatics at the Technical University and Ludwig-Maximilians-Universität in Munich
  • 2006-2007
  • Master Program in Computational Science and Engineering at the TU Munich
  • 2007-2008
  • Fast-Track Program of the Graduate School of Systemic Neurosciences and Elite Graduate Program Neurosciences (LMU Munich); Master Thesis: "Dynamic Receptive Fields of Motion-Sensitive Neurons"
  • since 2008
  • PhD at the Max Planck Institute of Neurobiology, Department of Systems and Computational Neuroscience (Prof. Alexander Borst). Project: Recurrent network interactions in the lobula plate of the fly

Scholarship
  • since 2008
  • member of the Graduate Program Motion and Orientation in Space and scholarship of the German Research Foundation (DFG)

Publication
  • F. Weber, H. Eichner, H. Cuntz & A. Borst; Eigenanalyis of a neural network in the fly; New Journal of Physics, 2008