RECEPTIVE FIELDS OF OPTIC TRACT AXONS AND LATERAL GENICULATE CELLS: PERIPHERAL EXTENT AND BARBITURATE SENSITIVITY

Publisher Website
Google Scholar
Abstract
In locally anesthetized cats, the influence of distant retinal areas on the receptive fields of optic tract (OT) axons and lateral geniculate (LGN) cells has been studied by stimulating the field center with liminal light and at the same time moving dark objects in the surround. Movement of a black disc in the periphery of the receptive field of an OT axon lowered the threshold for the center and for the surround adjacent the center. This was termed the Periphery Effect (PE) and could be obtained at angles up to 90 degrees or more from the center of the receptive field. The intensity of the PE was found to depend on (1) frequency or speed of movement of the disc, (2) amplitude of movement, (3) distance of movement from the field center, (4) size of object moved and (5) level of background illumination. Some semi-quantitative studies on the last 3 parameters were made. Evidence is presented that the PE as seen in OT axons represents an intra-retinal mechanism and is not an artifact of scattered light. LGN cells showed more complex responses than OT axons, giving PEs of acceleration, inhibition or both, or showing no effect at all. This variety of responses is thought to result from multiple inputs to single LGN cells. The PE was very sensitive to subanesthetic doses of barbiturates and showed a longer recovery time than did the responsiveness of the receptive field center. LGN cells could be influenced by moving black discs in the ipsilateral visual hemifield, indicating that at least some of the lateral interactions involved are occurring in the retina.