Electroreception: Extracting Behaviorally Important Signals from Noise

Sharks, skates, and rays exploit a marine environment rich in bioelectric and motional electric fields, which are very weak but nevertheless very useful for prey capture, predator avoidance, social interactions, and orientation in the sea. The elasmobranchs’ appreciation of these fields is made possible by two distinct specializations. The first of these is an array of extraordinarily sensitive receptors, the ampullae of Lorenzini, which derive much of their sensitivity from positive feedback mechanisms held delicately balanced at threshold. The second specialization is a sophisticated set of filter mechanisms in the brain for extracting the weak electrosensory signals from much stronger background noise. A large portion of this background noise is created by the fish’s own movements. Recent experiments show that a remarkable adaptive filter mechanism implemented by the cerebellar-like circuitry of the medullary electrosensory nucleus accounts for much of the noise suppression. The specializations of receptors and CNS so well developed in these fishes allow us to recognize important general principles operating in other sensory systems and in other vertebrates.