Biology subjects

Hladnik, T. C.

Publications and source records attributed to Hladnik, T. C..

3 recordsLinked to original sources

bioRxiv2026

MARINER: a surround visual stimulator for vision research in aquatic animals

Aquatic vertebrates are increasingly used in neuroscience research, yet underwater visual stimulation remains a challenge. Commonly used monochromatic stimuli have been shown to be inadequate to activate many visual neurons properly, and underwater refraction artifacts are prone to ruin stimulus designs. Here, we present MARINER - a visual stimulator, which remedies these issues and integrates concurrent behavioral and neurophysiological two-photon calcium imaging recordings. MARINERs full-field visual stimulation combined with receptive field mapping reveals that the visual field of larval zebrafish is larger than previously thought, extending almost down below the fish, and is spatially biased to better utilize motion content in naturalistic visual scenes. Using chromatic motion nulling, we further show that behavioral responses and task-associated sensory neurons are colorblind for "red" and "green" during the larvas optokinetic response. The MARINER stimulator facilitates naturalistic stimulation and faithful presentation of colored visual underwater stimuli for small aquatic species.

neuroscience↗

bioRxiv2025

Vertical Optokinetic Eye Movements in the Larval Zebrafish

The optokinetic response (OKR), a reflex enabling stable visual processing by minimizing retinal slip, has been well characterized in teleosts over the last decades. While previous work on teleost OKR mostly focused on its horizontal component, mammals are known to perform vertical and torsional OKR in addition to horizontal OKR. In this study, we characterize the vertical optokinetic response (vOKR) in larval zebrafish and compare it to the horizontal OKR (hOKR) and the vertical vestibulo-ocular reflex (vVOR). Our simultaneous camera-based tracking of vertical and horizontal eye positions reveals a distinct vOKR in larval zebrafish, but with a much smaller dynamic range compared to the hOKR and without any quick phases (resetting saccades). When presented with constant roll-rotating visual stimuli, zebrafish exhibit a brief initial vertical eye rotation in the direction of the stimulus, followed by a period without further slow phase response and interspersed with only spontaneous saccades. This behavior contrasts sharply with the periodical occurrence of resetting saccades (quick phases) during hOKR. The initial vertical response is tuned to similar spatial frequencies and angular velocities as the hOKR. We furthermore show that the vVOR has a much larger vertical dynamic range than the vOKR, demonstrating that the neuronal circuitry itself - and not the oculomotor plant - is the limiting factor. While it is unclear whether the observed differences in vertical versus horizontal optokinetic control have an adaptive value for zebrafish, the identified differences are drastic and informative for further studies on visuomotor circuits in teleosts. Summary StatementThis study characterizes the vertical optokinetic response (vOKR) in larval zebrafish, revealing differences from the horizontal OKR and providing insights into visual processing and eye movement control.

neuroscience↗

bioRxiv2025

Saccadic Suppression Enhances Saliency of Prey-Like Stimuli in the Optic Tectum

Saccadic suppression, a reduction in visual sensitivity around the time of rapid eye movements, is well-documented in primate psychophysics but its mechanisms and functions remain debated. Here, we use zebrafish to trace the origins of saccadic suppression and we demonstrate how saccadic suppression selectively enhances the visual salience of ecologically relevant stimuli. Saccadic suppression thus contributes to more than just compensation for rapid saccade-induced image shifts. We first established a behavioral correlate of saccadic suppression in larval zebrafish escape behavior. Then, using electrophysiology, we show that retinal ganglion cells jumpstart saccadic suppression in a spatial frequency dependent manner. Calcium imaging, combined with 360{degrees} visual stimulation and behavioral tracking, revealed that motor signals enhance peri-saccadic suppression strength in the optic tectum, where suppression lasts for more than 3000 ms. Notably, saccadic suppression is much weaker and more short-lived for stimuli related to hunting or escape behavior than for behaviorally less relevant global flashes. This unequal attenuation effectively increases the salience of the ecologically relevant stimuli in the optic tectum after saccades. Our results demonstrate that saccadic suppression integrates visual and motor signals to optimize sensory processing within neural constraints, and they provide insights into evolutionarily conserved visual strategies.

neuroscience↗