Abstract

The receptors of the mammalian retina, which all hyperpolarize to light, make signconserving synapses with OFF bipolars and sign-inverting synapses with ON bipolars. Several hypotheses have been generated to explain this arrangement. To test them we applied the neurotransmitter agonist 2-amino-4-phosphonobutyrate (APB) to the retina, which selectively blocks the ON bipolars. Two kinds of experiments were carried out: In one, we examined the visual responses of single cells while reversibly inactivating the ON channel with APB. In the other, we assessed the visual capacities of monkeys before and after the ON channel was blocked. Our single-cell recordings show that the ON and OFF channels remain segregated in the geniculo-striate system until the striate cortex, where they converge. The center/surround organization of the retinal ganglion cells and the orientation and direction-selectivity of cortical cells are not produced by interaction of the ON and OFF channels but by the lateral inhibitory networks. The behavioral experiments identify two reasons for the emergence of the ON and OFF channels: (1) to make possible the central transmission of both light-incremental and light-decremental information with excitatory processes and (2) to enhance contrast sensitivity.

© 1990 Optical Society of America