Figure 1.

Electrical signatures of fictive forward swims and turns in paralyzed fish. (A) Fictive virtual-reality setup. A larval zebrafish is paralyzed, head-embedded in agar or suspended from pipettes, and suction electrodes record activity from motor neuron axons. Motor neuron activity is used to simulate movement through a virtual environment which is projected on a display underneath the fish. A two-photon microscope records neuronal activity as reported by a genetically-encoded calcium indicator. Right: schematic of the correspondence between free swimming behavior and fictive behavior. In each case, the movement of the world, as seen from the fish's point of view, is the same. (B) Schematic of the optomotor response (OMR) in a freely swimming fish (top view). Fish turn and swim along with the direction of whole-field motion. (C) Schematic of the goal of the current work. Left: a freely swimming fish makes a left turn (top view). Right: a fictively swimming paralyzed fish intends to make a left turn, upon which the virtual environment projected underneath the fish shifts to induce the same optical translation as observed by the freely swimming fish. (D) Left: example of a fictive forward swim. This was elicited by forward, tail-to-head whole-field motion. The pixelized fish indicates that this is fictive behavior. Right: example of a fictive turn to the left, elicited by leftward whole-field motion. Thin lines depict electrical signal, thick lines represent the local standard deviation in a running window of 10 ms. Data in panels (D–H) is from one representative fish. (E) Additional examples of fictive turns and forward swim bouts. (F–H) Statistics of responses to whole-field motion in a typical fish. Each point on the graph represents a different direction of whole-field motion. The last point represents a static scene. (F) Probability of above-threshold activity occurring on the left or the right electrode for a typical fish. This open-loop behavior is similar to “virtual open loop” behavior observed in freely swimming fish (Orger et al., 2000). (G) Number of bursts per swim is largest for forward visual stimulation. (H) Number of swim bouts in a 10 s window increases with larger forward component of visual motion. (I) Difference in power of the left and right channels as a function of the direction of visual stimulation, showing a systematic relationship between these two variables, suggesting that left-right power difference may code for intended turn angle.