Räumlich-zeitliche Dynamik verteilter Netzwerk-Aktivität als Determinate zielgerichteter Verhaltensabfolgen im Nervensystem des Wirbeltiers
Final Report Abstract
Visually controlled, goal-directed motor sequences are crucial for the survival of an animal. Research in this project aimed at identifying fundamental neural mechanisms that enable an animal to rapidly analyze its sensory environment, to make behavioral decisions and to generate complex motor sequences. A critical question is how the central nervous system achieves the task to rapidly and reliably control our movements in response to a multitude of sensory stimuli in our immediate surround. One of the most imminent tasks of the visual system is to detect and classify moving objects and to select appropriate motor patterns, e.g. to approach a prey object or to avoid a predator. Here, we used zebrafish as a model system to investigate the neural circuits and synaptic mechanisms that underlie the processing of object motion and classification of object size. Zebrafish exhibit a repertoire of visually guided behaviors already at early larval stages, including target-directed prey capture sequences and object avoidance responses. To be able to study the underlying neural mechanisms, we first set out to obtain a quantitative understanding of what the fish sees and the types of motor patterns the fish uses during such rapidly occurring motor sequences. Information from this behavioral analysis allowed us to develop a closed-loop stimulus environment, in which we could elicit target-directed motor sequences and rapid behavioral choice. This approach offered the opportunity to study patterns of neural activity while the nervous system performed specific processing steps, and we applied this approach to search for circuit motifs in the visual system contributing to visual motion processing and object size classification. A first and surprising outcome of this project was the discovery of genetically specified neural cell types in a major retinal target area, the optic tectum, that were selective for opposing directions of motion of moving stimuli. Two cell types were found that exhibited distinct morphologies and targeted different retinorecipient layers consistent with their opposing directional tuning curves. Remarkably, these cell types received directionally tuned excitatory synaptic inputs, which most likely come from retinal afferent fibers with corresponding directional tuning, since these were found to arborize in nearby but distinct tectal layers. This unexpected finding immediately suggested an elegant mechanism for how direction selectivity emerges during development in visual centers downstream of the retina. In a subsequent study, we set out to identify the visual circuitry that may play a vital role in stimulus classification underlying behavioral choice. The earlier behavioral analysis showed a switch in swimming direction depending on the size of a moving object. Using calcium imaging, we found that different sets of retinal ganglion cell fibers in the tectum respond to these behaviorally distinct object size classes. Using single cell patch clamp recordings, we found that a class of horizontal tectal neurons received specific synaptic inputs from these size-selective input fibers, depending on which neuropil layer in the tectum their dendrites were localized. Further downstream, distinct subgroups of tectal neurons were active in the presence of either small or large objects, corresponding to those sizes that evoke targetdirected or avoidance swims. Together, these findings suggest a general network architecture, in which the tectum may represent a bifurcation point where stimulus classification biases the decision between mutually exclusive responses (‘‘move toward or away’’), thus contributing to adequate response selection. http://www.mpg.de/8416636/zebrafish-eye http://www.mpg.de/7259556/hunting-behaviour-zebrafish-larvae?filter_order=LT&research_topic=BM-NB http://www.bio-pro.de/magazin/index.html?lang=de&artikelid=/artikel/09567/index.html
Publications
- (2012). Layer-specific targeting of direction-selective neurons in the zebrafish optic tectum. Neuron 76, 1147-1160
Gabriel, J.P., Trivedi, C.A., Maurer, C.M., Ryu, S., and Bollmann, J.H.
(See online at https://doi.org/10.1016/j.neuron.2012.12.003) - (2013). Visually driven chaining of elementary swim patterns into a goal-directed motor sequence: a virtual reality study of zebrafish prey capture. Frontiers in Neural Circuits 7, 86
Trivedi, C.A., and Bollmann, J.H.
(See online at https://doi.org/10.3389/fncir.2013.00086) - (2014). Classification of object size in retinotectal microcircuits. Current Biology 24, 2376-2385
Preuss, SJ, Trivedi, CA, Maurer, CM, Ryu, S, and Bollmann, JH
(See online at https://doi.org/10.1016/j.cub.2014.09.012)
