INVESTIGATION OF THE EFFECTS OF PERCEPTUAL SALIENCE ON TARGET TRACKING BEHAVIOR PERFORMANCE OF ZEBRAFISH DURING RHEOTAXIS

Abstract

Zebrafish (Danio rerio) are freshwater fish inhabiting rivers and lakes in the South Asian region. During their behavior known as rheotaxis, they exhibit a tendency to orient their bodies againts the water flow, thereby displaying station keeping. Objects present in the flowing water can create areas of reduced current velocity behind them by obstructing the flow in specific regions. Particularly in situations of high current velocity ( > 0.5m/s ), fish seek refuge behind such objects to avoid being carried away by the current. One of the most important problems that may arise in the system description of multimodal sensory integration dynamics is that sensory salience profoundly affects behavioral control. Perceptual salience is the tendency for one sensory system to become more dominant or salient compared to the others. Particularly salient sensory inputs are processed more dominantly by the Central Nervous System (CNS), which in turn shapes behavioral responses. For example, experiments on zebrafish have shown the effect of sensory salience when studying the fish's swimming behavior against a current (rheotaxis). In a custom-built speed-controlled swim tunnel, a D-shaped tube was placed to alter the flow. It produced mechanosensory cues upon movement, while its red inner stick elicited visual stimuli, tracked by the fish. While the zebrafish followed these visual and mechanosensory signals, the weights of the relevant sensory signals were rapidly updated by the CNS according to the sensory salience levels. Therefore, understanding the impact of perceptual salience on multi-sensory integration dynamics is one of the main objectives of this thesis. We utilized tubes of different sizes (2cm, 4cm, and 6cm in diameter) made of red-colored 3D printed material and plexiglass (6cm) to locally disrupt water flow in a speed-controlled experimental setup. The tubes were moved sinusoidally by a motor at frequencies of 0.05Hz, 0.10Hz, 0.25Hz, 0.55Hz, and 0.95Hz. The experimental conditions encompass four different stages: 1) Attaching a 6cm plexiglass tube outside the 2cm, 4cm, and 6cm red tubes in a well-lit environment, 2) Conducting the experiment without attaching the 6cm plexiglass tube outside the 2cm, 4cm, and 6cm red tubes in a well-lit environment, 3) Attaching a 6cm plexiglass tube outside the 2cm, 4cm, and 6cm red tubes in a dark environment, 4) Conducting the experiment without attaching the 6cm plexiglass tube outside the 2cm, 4cm, and 6cm red tubes in a dark environment. These perceptual salience conditions were tested with N=5 fish. Analysis of the results indicates that fish exhibit superior tracking behavior at lower frequencies compared to higher frequencies. Furthermore, as the diameter increases, the consistency of the tracking behavior improves, resulting in enhanced performance. This suggests that the mechanosensory system plays a more dominant role in tracking behavior of zebrafish. However, when the visual system is also engaged, tracking behavior becomes more consistent. The integration of these two sensory systems allows for more effective responses to environmental stimuli. This information may have potential applications in the treatment of multisensory disorders, and the novel experimental setup we designed, which is not yet reported in the literature, may be a valuable tool for disease diagnosis, treatment, and future research.