Desegregation: Bussing of Signals Through the Retinal Network

Abstract

One of the information processing principles that has been repeatedly discovered in the nervous system is the segregation of signals into separate but parallel pathways. In the visual system, for example, separationist groups such as ocular dominance and orientation columns have been uncovered in the visual cortex (8). This reactionary processing is also prominent in the retina where there is an apparent separation of rod-cone, ON-OFF, and transient-sustained signals (7,9,11, 23). These various modalities decompose images from the outside world into informational components that can be processed by the nervous system. This model of sensory processing proposes that images from the outside world are handled by a multiplicity of parallel pathways, each relaying information about a particular characteristic of the external image, such as its color, orientation, or direction of motion. This theory has found strong support in the discovery of neurons that are preferentially stimulated by one of these trigger features (2,12). Although this appears to be an important mechanism in sensory systems, recent studies in amphibian retina suggest that the segregation of signals is not so absolute, and that in fact there may be a mixing of signals which at face value seems to contradict the principles of decomposition and segregation that enables animals to interpretation the visual world.