38 research outputs found

    Channeling of red and green cone inputs to the zebrafish optomotor response

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    Whole-Brain Activity Maps Reveal Stereotyped, Distributed Networks for Visuomotor Behavior

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    Most behaviors, even simple innate reflexes, are mediated by circuits of neurons spanning areas throughout the brain. However, in most cases, the distribution and dynamics of firing patterns of these neurons during behavior are not known. We imaged activity, with cellular resolution, throughout the whole brains of zebrafish performing the optokinetic response. We found a sparse, broadly distributed network that has an elaborate but ordered pattern, with a bilaterally symmetrical organization. Activity patterns fell into distinct clusters reflecting sensory and motor processing. By correlating neuronal responses with an array of sensory and motor variables, we find that the network can be clearly divided into distinct functional modules. Comparing aligned data from multiple fish, we find that the spatiotemporal activity dynamics and functional organization are highly stereotyped across individuals. These experiments systematically reveal the functional architecture of neural circuits underlying a sensorimotor behavior in a vertebrate brain.Molecular and Cellular Biolog

    Perception of Fourier and non- Fourier motion by larval zebrafish

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    articles Zebrafish larvae innately begin responding to moving stimuli shortly after hatching. In their optomotor response, which is elicited by large moving stimuli presented from below or the side 1,2 , larvae swim in the direction of perceived motion. The distance they travel in a given time indicates the effectiveness of the stimulus. By observing the response of many larvae to computer-animated displays, we could determine which attributes of a moving stimulus the zebrafish visual system detects. If luminance-defined features drift smoothly or jump in space, they can produce strong sensations of motion. A number of proposed models explain how motion information can be extracted. In a simple model, a point-to-point comparison is made between the luminance pattern and a spatially displaced copy of the pattern that was seen a short time before 3 . The displacement that gives the best fit tells the brain the direction and speed of movement. A more complex strategy is to look at the Fourier motion energy in the visual scene Although there is evidence that humans can use both feature matching and motion energy to detect movement 7 , they may also sense motion when presented with stimuli in which only secondorder features such as contrast, texture or flicker are moving Here we find that the fish larvae detect moving features of visu- A moving grating elicits innate optomotor behavior in zebrafish larvae; they swim in the direction of perceived motion. We took advantage of this behavior, using computer-animated displays, to determine what attributes of motion are extracted by the fish visual system. As in humans, first-order (luminance-defined or Fourier) signals dominated motion perception in fish; edges or other features had little or no effect when presented with these signals. Humans can see complex movements that lack first-order cues, an ability that is usually ascribed to higher-level processing in the visual cortex. Here we show that second-order (non-Fourier) motion displays induced optomotor behavior in zebrafish larvae, which do not have a cortex. We suggest that second-order motion is extracted early in the lower vertebrate visual pathway. al stimuli in a way that is qualitatively similar to humans: both firstorder and second-order cues drive their behavioral response. Our demonstration of second-order motion detection in fish challenges the idea that higher-level, cortical mechanisms are necessary to explain this capacity of the visual system. RESULTS Optomotor responses to Fourier motion The assay used to measure optomotor responses is similar to the one described previously 2 (Methods). Movies showing drifting gratings evoke strong optomotor responses in almost all fish in a clutch. Fish do not respond to a moving grating with a stripe width narrower than approximately 9°, which is slightly less than the predicted resolution limit of the larval cone mosaic, 6°at this age In the following experiments, responses were normalized to the effect of a designated strong stimulus, a 100% contrast square wave subtending 100°of visual angle per cycle and moving at 1 Hz for 30 seconds Although the fish seemed to follow a motion signal in the movies, it was possible that they were tracking features such as light or dark regions or edges that were being displaced. We did an experiment to show that the optomotor response is truly a response to motion. A motion display was shown of a sine wave grating tha

    Forward Genetic Analysis of Visual Behavior in Zebrafish

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    The visual system converts the distribution and wavelengths of photons entering the eye into patterns of neuronal activity, which then drive motor and endocrine behavioral responses. The gene products important for visual processing by a living and behaving vertebrate animal have not been identified in an unbiased fashion. Likewise, the genes that affect development of the nervous system to shape visual function later in life are largely unknown. Here we have set out to close this gap in our understanding by using a forward genetic approach in zebrafish. Moving stimuli evoke two innate reflexes in zebrafish larvae, the optomotor and the optokinetic response, providing two rapid and quantitative tests to assess visual function in wild-type (WT) and mutant animals. These behavioral assays were used in a high-throughput screen, encompassing over half a million fish. In almost 2,000 F2 families mutagenized with ethylnitrosourea, we discovered 53 recessive mutations in 41 genes. These new mutations have generated a broad spectrum of phenotypes, which vary in specificity and severity, but can be placed into only a handful of classes. Developmental phenotypes include complete absence or abnormal morphogenesis of photoreceptors, and deficits in ganglion cell differentiation or axon targeting. Other mutations evidently leave neuronal circuits intact, but disrupt phototransduction, light adaptation, or behavior-specific responses. Almost all of the mutants are morphologically indistinguishable from WT, and many survive to adulthood. Genetic linkage mapping and initial molecular analyses show that our approach was effective in identifying genes with functions specific to the visual system. This collection of zebrafish behavioral mutants provides a novel resource for the study of normal vision and its genetic disorders

    Graph Theoretical Model of a Sensorimotor Connectome in Zebrafish

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    Mapping the detailed connectivity patterns (connectomes) of neural circuits is a central goal of neuroscience. The best quantitative approach to analyzing connectome data is still unclear but graph theory has been used with success. We present a graph theoretical model of the posterior lateral line sensorimotor pathway in zebrafish. The model includes 2,616 neurons and 167,114 synaptic connections. Model neurons represent known cell types in zebrafish larvae, and connections were set stochastically following rules based on biological literature. Thus, our model is a uniquely detailed computational representation of a vertebrate connectome. The connectome has low overall connection density, with 2.45% of all possible connections, a value within the physiological range. We used graph theoretical tools to compare the zebrafish connectome graph to small-world, random and structured random graphs of the same size. For each type of graph, 100 randomly generated instantiations were considered. Degree distribution (the number of connections per neuron) varied more in the zebrafish graph than in same size graphs with less biological detail. There was high local clustering and a short average path length between nodes, implying a small-world structure similar to other neural connectomes and complex networks. The graph was found not to be scale-free, in agreement with some other neural connectomes. An experimental lesion was performed that targeted three model brain neurons, including the Mauthner neuron, known to control fast escape turns. The lesion decreased the number of short paths between sensory and motor neurons analogous to the behavioral effects of the same lesion in zebrafish. This model is expandable and can be used to organize and interpret a growing database of information on the zebrafish connectome
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