Representation of Borders and Swimming Kinematics in the Brain of Freely-Navigating Fish

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. However, virtually nothing is known about how fish represent space and locomotion in the brain to enable successful navigation. Using a novel wireless 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 water tank. Three cell types were identified: border cells, velocity cells and speed cells. Border cells are active when the fish is near the boundary of the environment. Velocity cells encode swimming direction and speed and can represent the direction needed for navigation. Speed cells only encode the absolute speed independent of direction and may provide an odometry signal. This study is thus the first to address the question of how information relevant for navigation may be represented in the fish brain, and address the fundamental question of the neural basis of navigation in this diverse group of vertebrates. The similarities between our observations in fish and earlier findings in mammals may indicate that the networks controlling navigation in vertebrate originate from a common ancient circuit.