Central processing of sensory information in electric fish.

Comparative studies of neural mechanisms underlying the perception of natural stimulus patterns and the control of adaptive behavioral responses have revealed organizational principles that are shared by a wide spectrum of animals. Mechanisms of perception and motor control are commonly executed in a distributed network of neurons that lack 'pontifical' elements. Individual neurons even at an organizational level as high as the optic tectum may still have very general response characteristics, and the recruitment of individual neurons reveals little about the nature of the stimulus situation outside. Only the joint evaluation of messages from large populations of such neurons yields unambiguous pictures of the outside world. Stimulus variables are commonly mapped continuously within a stratum of neurons so that their variation over time can be monitored by mechanisms similar to motion detection in a retina. The ordered representation of a stimulus variable within an array of broadly tuned elements allows for a degree of stimulus resolution that by far exceeds that of individual elements in the array. Neural systems are burdened by their evolutionary history and suffer from imperfections that are overcome by a patchwork of compensations. The existence of multiple neuronal representations of sensory information and multiple circuits for the control of behavioral responses should provide the necessary freedom for evolutionary tinkering and the invention of new designs.