Biology subjects

Baier, H.

Publications and source records attributed to Baier, H..

24 records · Page 2Linked to original sources

bioRxiv2019

Deconstructing hunting behavior reveals a tightly coupled stimulus-response loop

Animals build behavioral sequences out of simple stereotyped actions. A comprehensive characterization of these actions and the rules underlying their temporal organization is necessary to understand sensorimotor transformations performed by the brain. Here, we use unsupervised methods to study behavioral sequences in zebrafish larvae. Generating a map of swim bouts, we reveal that fish modulate their tail movements along a continuum. We cluster bouts that share common kinematic features and contribute to similar behavioral sequences into seven modules. Behavioral sequences comprising a subset of modules bring prey into the anterior dorsal visual field of the larvae. Fish then release a capture maneuver comprising a stereotyped jaw movement and fine-tuned stereotyped tail movements to capture prey at various distances. We demonstrate that changes to chaining dynamics, but not module production, underlie prey capture deficits in two visually impaired mutants. Our analysis thus reveals the temporal organization of a vertebrate hunting behavior, with the implication that different neural architectures underlie prey pursuit and capture.

neuroscience↗

bioRxiv2019

Light-sheet imaging and graph-theoretical analysis of antidepressant action in the larval zebrafish brain network

The zebrafish is increasingly being employed as an experimental platform to model neuropsychiatric diseases and to screen for novel neuro-active compounds. While the superb genetic and optical access that this system offers has long been recognized, these features have not been fully exploited to investigate disease mechanisms and possible therapeutic interventions. Here we introduce a light-sheet imaging and graph-theoretical analysis pipeline to determine the effects of the known or suspected antidepressant compounds fluoxetine, ketamine and cycloserine on brain-wide neural activity patterns. We imaged the brains of both wildtype fish and grs357 mutants, which harbor a missense mutation that abolishes glucocorticoid receptor transcriptional activity. The grs357 mutation results in a chronically elevated stress axis together with behavioral endophenotypes of depression. Consistent with broad expression of the glucocorticoid receptor throughout the brain, we show that the mutant fish exhibit an altered correlational structure of resting-state brain activity. Intriguingly, in grs357 mutant fish, an increased modularity, which represents the degree of segregation of the network into highly clustered modules, was restored by acute fluoxetine administration to wildtype levels. Ketamine and cycloserine also normalized specific parameters of the graph. Fluoxetine altered network function in the same direction in mutant and wildtype, while ketamine and cycloserine had effects that were opposite for the two genotypes. We propose that light-sheet imaging, followed by graph analysis, is a content-rich and scalable first-pass approach for studying the neural consequences of drug effects and drug x genotype interactions in zebrafish models of psychiatric disorders.

neuroscience↗

bioRxiv2019

Zebrafish use visual cues and geometric relationships to form a spatial memory

Animals use salient cues to navigate in their environment, but their specific cognitive strategies are largely unknown. We developed a conditioned place avoidance paradigm to discover whether and how zebrafish form spatial memories in a Y-shaped maze. Juvenile zebrafish, older than three weeks, learned to avoid the arm of the maze that was cued with a mild electric shock. We found that the fish required distinct visual patterns to develop a conditioned response. Interestingly, individual fish solve this task in different ways: by staying in the safe center of the maze, by preference for one, or both, of the safe patterns, or by mixed strategies. In experiments in which the learned patterns were swapped, rotated or replaced, the animals could transfer the association of safety to a different arm or to a different pattern using either visual cues or location as the conditioned stimulus. These findings show that juvenile zebrafish exhibit several complementary spatial learning modes and pave the way for neurobiological studies of navigational mechanisms in this model species.

neuroscience↗

bioRxiv2019

Neuronal circuitry for stimulus selection in the visual system

Visual objects naturally compete for the brains attention, and selecting just one of them for a behavioural response is often crucial for the animals survival1. The neural correlate of such stimulus prioritisation might take the form of a saliency map by which responses to one target are enhanced relative to distractors in other parts of the visual field2. Single-cell responses consistent with this type of computation have been observed in the tectum of primates, birds, turtles and lamprey2-7. However, the exact circuit implementation has remained unclear. Here we investigated the underlying neuronal mechanism presenting larval zebrafish with two simultaneous looming stimuli, each of which was able to trigger directed escapes on their own. Behaviour tracking revealed that the fish respond to these competing stimuli predominantly with a winner-take-all strategy. Using brain-wide functional recordings, we discovered neurons in the tectum whose responses to the target stimulus were non-linearly modulated by the saliency of the distractor. When the two stimuli were presented monocularly in different positions of the visual field, stimulus selection was already apparent in the activity of retinal ganglion cell axons, a likely consequence of antagonistic mechanisms operating outside the classical receptive field8,9. When the two stimuli were presented binocularly, i.e., on opposite sides of the fish, our analysis indicates that a loop involving excitatory and inhibitory neurons in the nucleus isthmi (NI) and the tectum weighed stimulus saliencies across hemispheres. Consistent with focal enhancement and global suppression, glutamatergic NI cells branch locally in the tectum, whereas GABAergic NI cells project broadly across both tectal hemispheres. Moreover, holographic optogenetic stimulation confirmed that glutamatergic NI neurons can modulate visual responses in the tectum. Together, our study shows, for the first time, context-dependent contributions of retinotectal and isthmotectal circuits to the computation of the visual saliency map, a prerequisite for stimulus-driven, bottom-up attention.

neuroscience↗

bioRxiv2018

Biological motion as an innate perceptual mechanism driving social affiliation

Collective behavior, such as shoaling in teleost fish, is driven by the perceptual recognition of conspecific animals. Because social interactions are mutual, it has been difficult to disentangle the exact sensory cues that trigger affiliation in the first place from those that are emitted by receptive and responsive shoal mates. Here we overcome this challenge in a virtual reality assay in zebrafish. We discovered that simple visual features of conspecific biological motion provide an irresistible shoaling cue. Individual juvenile fish interact with circular black dots projected onto a screen, to the same extent as they do with real conspecifics, provided these virtual objects mimic the characteristic kinetics of zebrafish swim bouts. Other naturalistic cues previously implicated in shoaling, such as fish-like shape, pigmentation pattern, or non-visual sensory modalities are not required. During growth, the animals stimulus preferences shift gradually, matching self-like kinetics, even in fish raised in isolation. Virtual group interactions and our multi-agent model implementation of this perceptual mechanism demonstrate sufficiency of kinetic cues to drive assortative shoaling, a phenomenon commonly observed in field studies. Coordinated behavior can emerge from autonomous interactions, such as collective odor avoidance in Drosophila, or from reciprocal interactions, such as the codified turn-taking in wren duet singing. We found that individual zebrafish shoal autonomously without evidence for a reciprocal choreography. Our results reveal individual-level, innate perceptual rules of engagement in mutual affiliation and provide experimental access to the neural mechanisms of social recognition. (239/250 words max)\n\nSignificance StatementSocial affiliation is ubiquitous in the animal kingdom, but fundamental sensory cues driving group formation remain elusive. During swarm behavior, for example, individuals dynamically exchange sensory cues with their neighbors, presenting an intertwined choreography opaque to formal analysis of causal stimulus-response relationships. Using a virtual interaction assay for psychophysical analysis, we solved this issue and identify biological motion as the irresistible trigger of social affiliation in zebrafish, Danio rerio. Given that many species form groups including shoals, flocks and herds, perceptual mechanisms of social recognition and their underlying neural circuits are likely shared across vertebrates. The identification of fundamental affiliation-inducing cues is a prerequisite for relating individual-level sensory-motor transformations to collective behavior. (112/120 words max)

neuroscience↗

bioRxiv2017

Detection of whole-field luminance changes by superficial interneurons in the zebrafish tectum

The superficial interneurons, SINs, of the zebrafish tectum, also known as tectal horizontal cells, have been implicated in a range of behavioral responses to visual cues, including prey capture and looming-evoked escape. However, there is limited information on their tuning properties, synaptic connectivity and molecular diversity. We have begun to close this gap in our knowledge by performing functional GCaMP6 imaging and electrophysiological recordings of SIN responses to simplified stimuli. We found that a large subset of the SINs strongly responded to luminance changes, with a preference for OFF steps. Although SINs were generally tuned to any dark-light, or light-dark, transition, they were often most sensitive to a narrow range of luminance steps. Tuning properties did not vary with the position of the SIN cell body along the depth of the tectal neuropil or with the orientation of the cell neurites within the neuropil. Receptive field (RF) mapping revealed that SINs sample over large areas of the visual field (greater than 20 degrees, typically 50 degrees). RFs of individual SINs were sometimes spatially incoherent, indicating that SINs may receive sparse inputs from multiple RGCs scattered widely over the retina. Lastly, we found that, while most SINs express GABAergic markers, as reported before, a substantial minority express a vesicular glutamate transporter. We propose that the role of the SINs is more complex than previously reported, and provide evidence that at least one SIN subtype could function as a multi-purpose circuit element for signaling changes in ambient luminance for subsequent processing in the tectum.

neuroscience↗