TRANSFER CHARACTERISTICS OF X-LGN NEURONS IN CATS REARED WITH EARLY DISCORDANT BINOCULAR VISION

1. The effects of early discordant binocular vision on the functional development of the cat lateral geniculate nucleus (LGN) were investiga ted by quantitatively comparing responses of individual LGN neurons wi th their direct retinal inputs. 2. Unilateral convergent strabismus (e sotropia) was surgically induced in 11 kittens at the age of 3 wk. Aft er the animals had reached 9 mo of age, extracellular microelectrode r ecordings were made from individual X LGN units in laminae A and Al of anesthetized and paralyzed cats. Responses were measured for drifting sinusoidal gratings. Within unit comparisons of LGN action potentials (LGN output) and S potentials (retinal input) were performed to deter mine the nature of signal transfer in the units driven by the deviatin g (N = 42) or nondeviating eyes (N = 29) of strabismic cats. The resul ts were compared with similar data (N = 29) obtained from nine normal control cats. 3. The spatial resolution of many individual LGN units i n strabismic cats was abnormally reduced relative to their retinal inp uts. These differences were more pronounced in units that received inp uts from the nasal retina of the contralateral eye. The resolution los s was closely associated with a dramatic decrease in the strength of t he receptive field center mechanism of LGN units relative to their ret inal inputs. Moreover, the efficiency of signal transfer for high-spat ial-frequency stimuli, determined by the transfer ratio (response ampl itude of LGN action potentials/amplitude of S potentials), was signifi cantly lower in strabismic cats compared with normal controls. 4. In s trabismic cats, contrast thresholds for the action potentials of indiv idual LGN units were significantly higher than those determined for th e S potentials. In normal cats, the input-output differences in contra st threshold were negligible. The observed contrast sensitivity loss w as more pronounced for high-spatial-frequency stimuli. 5. The speed of signal transfer was significantly decreased in the LGNs of strabismic animals. The visual response latencies of many, but not all, X LGN ce lls in the strabismic cats were abnormally long when compared with tho se in normal control units, whereas SP latencies were virtually the sa me for strabismic and normal cats. Abnormal latencies were prevalent i n units that exhibited contrast threshold deficits, and were more seve re among the units receiving input from the contralateral nasal retina . 6. The deficits in strabismic cats were found in the LGN units inner vated by the deviating and nondeviating eyes. However, for the majorit y of response measures, the units innervated by the deviating eyes sho wed notably larger deficits. 7. We conclude that the fidelity of signa l transfer from the retina to the LGN is significantly reduced in cats reared with discordant binocular visual experience. Thus the adverse effects of early strabismus are not confined, at least in cats, to the visual cortex.