Biology subjects

Lavian, H.

Publications and source records attributed to Lavian, H..

4 recordsLinked to original sources

bioRxiv2025

A multi-ring shifter network computes head direction in zebrafish

From insects to fish to mammals, many species have an internal compass: a set of recurrently connected neurons that combine motor feedback, vestibular signals, and external cues to compute the animals heading direction. Whether the underlying mechanism is universal across different species is unresolved. In Drosophila, for instance, the central complex contains three connected, yet anatomically separate, functional neuron rings. Two rings receive countervailing velocity signals that shift neuronal activity bumps around all three rings. An alternative, classical continuous-attractor model invokes only one ring but requires velocity-modulated synaptic connections. A single-ring compass has been discovered in the anterior hindbrain of zebrafish. Using theory and experiments, we find, however, that three rings, including two shifter rings, are intermingled on the same anatomical scaffold. Zebrafish and Drosophila, therefore, use the same basic compass mechanism, suggestive of convergent evolution.

neuroscience↗

bioRxiv2024

The representation of visual motion and landmark position aligns with heading direction in the zebrafish interpeduncular nucleus

Sensory information is fundamental for navigation. Visual motion is used by animals to estimate their traveling distance and direction, and visual landmarks allow animals to tether their location and orientation to their environment. How such signals are integrated in the vertebrate brain is poorly understood. Here we investigate the representation of directional whole field visual motion and landmark position in a circuit in the larval zebrafish consisting of the habenula, interpeduncular nucleus (IPN) and anterior hindbrain (aHB). This circuit has been recently implicated in the representation of heading direction. Using calcium imaging we show that these stimuli are represented in the habenula, IPN and aHB. We further show that their representation in the IPN of both these stimuli is topographically arranged in a way that aligns itself with the representation of the heading signal in this region. We use neuronal ablations to show that the landmark responses, but not the whole field motion responses, require intact habenula input to the IPN. Overall our findings suggest the IPN as a site for integration of the heading signal from the aHB with visual information, shedding light on how different types of navigational signals are processed in the vertebrate brain.

neuroscience↗

bioRxiv2022

Neural dynamics and architecture of the heading direction circuit in a vertebrate brain

Animals can use different strategies to navigate. They may guide their movements by relying on external cues in their environment or, alternatively, by using an internal cognitive map of the space around them and their position within it. An essential part of this representation are heading cells, neurons whose activity depends on the heading direction of the animal. Although those cells have been found in vertebrates, the full network has never been observed and there is very little mechanistic understanding of how these cells acquire their response properties. In this study, we use volumetric functional imaging in larval zebrafish to observe, for the first time in a vertebrate, a full network that encodes allocentric heading direction. This network of approximately one hundred inhibitory neurons is arranged in an anatomical circle in the anterior hindbrain. Its activity is driven purely by the integration of internally generated signals, indicating that a simple vertebrate brain can encode maps of how an animal moves within its surroundings. Single cell reconstructions of electron micrographs allow us to uncover how the connectivity pattern of neurons within the network supports the implementation of a ring attractor network. The neurons we identify share features with neurons in the dorsal tegmentum nucleus of rodents and the fly central complex, showing that similar connectivity and mechanistic principles underlie the generation of cognitive maps of heading direction across the animal kingdom.

neuroscience↗

bioRxiv2018

Information transmission in a constitutively active GABAergic synapse

Short-term depression is a low pass filter of synaptic information that reduces and flattens synaptic information transfer at high presynaptic firing frequencies. This view questions the relevance of spontaneous high firing rates in some networks. In the indirect pathway of the basal ganglia, spontaneously active neurons in the globus pallidus (GP) form depressing inhibitory synapses in the basal ganglia output nuclei. Using numerical modeling and whole-cell recordings from single entopeduncular nucleus (EP) neurons in rat brain slices we investigated the contribution of the different firing rates of GP neurons to information transmission in the indirect pathway. Wholecell recordings showed significant variability in steady-state depression which decreased as stimulation frequency increased. Modeling predicted that this variability would translate into different postsynaptic noise levels during constitutive presynaptic activity. Our simulations further predicted that individual GP-EP synapses mediate gain control. However, when we consider integration of multiple inputs, the large range of GP firing rates would enable different modes of information transmission in which the magnitude and temporal features of postsynaptic modulation would change as a function of present and past firing rates of GP neurons. Finally, we predict that changes in dopamine levels can shift the action of GP neurons from rate coding to gain modulation. Our results thus demonstrate how short-term synaptic depression shapes information transmission in the basal ganglia in particular and via GABAergic synapses in general.\n\nSignificant statementSynapses displaying short-term depression are low-pass filters of synaptic input. Consequently, when presynaptic firing is high, little information passes to the postsynaptic neuron. However, many neurons fire at relatively high frequencies all the time. Are their synapses constantly silenced by depression? We tested this apparent contradiction in the indirect pathway of the basal ganglia, where neurons from the globus pallidus (GP) form constitutively active depressing synapses on basal ganglia output. We hypothesized that the different rates of ongoing activity underlie different modes of action for GP neurons. We show that the synaptic and structural properties of the indirect pathway map GP baseline frequencies to different postsynaptic signals, thus demonstrating how short-term synaptic depression shapes information transmission in the basal ganglia.

neuroscience↗