Like most animals, the survival of fish depends on navigation in space. This capacity has been documented in behavioral studies that have revealed navigation strategies. However, little is known about how freely swimming fish represent space and locomotion in the brain to enable successful navigation. Using a wireless neural recording system, we measured the activity of single neurons in the goldfish lateral pallium, a brain region known to be involved in spatial memory and navigation, while the fish swam freely in a two-dimensional water tank. We found that cells in the lateral pallium of the goldfish encode the edges of the environment, the fish head direction, the fish swimming speed, and the fish swimming velocity-vector. This study sheds light on how information related to navigation is represented in the brain of fish and addresses the fundamental question of the neural basis of navigation in this group of vertebrates.

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Recent years have witnessed a significant increase in the use of spontaneous Brillouin spectrometers for non-contact analysis of soft matter, such as aqueous solutions and biomaterials, with fast acquisition times. Here, we discuss the assembly and operation of a Brillouin spectrometer that uses stimulated Brillouin scattering (SBS) to measure stimulated Brillouin gain (SBG) spectra of water and lipid emulsion-based tissue-like samples in transmission mode with <10 MHz spectral-resolution and <35 MHz Brillouin-shift measurement precision at <100 ms. The spectrometer consists of two nearly counter-propagating continuous-wave (CW) narrow-linewidth lasers at 780 nm whose frequency detuning is scanned through the material Brillouin shift. By using an ultra-narrowband hot rubidium-85 vapor notch filter and a phase-sensitive detector, the signal-to-noise-ratio of the SBG signal is significantly enhanced compared to that obtained with existing CW-SBS spectrometers. This improvement enables measurement of SBG spectra with up to 100-fold faster acquisition times, thereby facilitating high spectral-resolution and high-precision Brillouin analysis of soft materials at high speed.

Navigation is one of the most fundamental cognitive skills for the survival of fish, the largest vertebrate class, and almost all other animal classes. Space encoding in single neurons is a critical component of the neural basis of navigation. To study this fundamental cognitive component in fish, we recorded the activity of neurons in the central area of the goldfish telencephalon while the fish were freely navigating in a quasi-2D water tank embedded in a 3D environment. We found spatially modulated neurons with firing patterns that gradually decreased with the distance of the fish from a boundary in each cell’s preferred direction, resembling the boundary vector cells found in the mammalian subiculum. Many of these cells exhibited beta rhythm oscillations. This type of spatial representation in fish brains is unique among space-encoding cells in vertebrates and provides insights into spatial cognition in this lineage.

Like most animals, the survival of fish depends crucially on navigation in space.This capacity has been documented in numerous behavioral studies that have revealed navigation strategies and the sensory modalities used for navigation. All rights reserved. No reuse allowed without permission.(which was not peer-reviewed) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity.The copyright holder for this preprint . http://dx.doi.org/10.1101/291013 doi: bioRxiv preprint first posted online Mar. 28, 2018; Navigation is a fundamental behavioral capacity facilitating survival in many animal species (4-7). It involves the continuous estimation and representation of the agent's position and direction in the environment which are implemented in the planning and execution of movements and trajectories towards target locations (8,9). Navigation has been investigated extensively on numerous taxa across the animal kingdom but attempts to probe its neural substrate have mainly been focused on mammals (10) and insects (11). In mammals, neurons in the hippocampal formation encode information about the position and orientation of the animal in space (8-10, 12, 13 (18,19). In insects, a ring-shaped neural network in the central complex of fruit fly was shown to represent its heading direction (11).To better understand space representation in other taxa, we explored the neural substrate of navigation in the goldfish (Carassius auratus). These fish are known to be able to navigate either by exploiting an allocentric or an egocentric frame of reference.This may imply that the goldfish has the ability to build an internal representation of space in the form of a cognitive map (3). This would include cognitive map-like navigation strategies to find a goal when starting from an unfamiliar initial position, or taking shorter alternative routes (shortcuts) when possible (2,3,20,21). Furthermore, goldfish use many environmental cues, such that any single cue would not be crucial in itself to navigating in the environment (21).In addition to these behavioral studies, lesion studies on goldfish have shown that the telencephalon is crucial for spatial navigation. Damage to the lateral pallium in the telencephalon leads to dramatic impairment in allocentric spatial memory and learning, but not when the lesion affects other parts of the telencephalon (21). These finding are similar to results from lesions studies of the hippocampus in mammals and further confirm that the lateral pallium in goldfish is a possible homologue of the mammalian All rights reserved. No reuse allowed without permission.(which was not peer-reviewed) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity.The copyright holder for this preprint . http://dx.doi.org/10.1101/291013 doi: bioRxiv preprint first posted online Mar. 28, 2018; hippocampus (3, 22) (but see also (23)). While these works have contributed to suggesting where the possible navigation mechanism is located in the...