No abstract

We describe experiments on behaving rats with electrodes implanted on the cornea, in the optic chiasm, and on the visual cortex; in addition, two red light-emitting diodes (LED) are permanently attached to the skull over the left eye. Recordings timelocked to the LED flashes reveal both the local events at each electrode site and the orderly transfer of visual information from retina to cortex. The major finding is that every stimulus, regardless of its luminance, duration, or the state of retinal light adaptation, elicits an optic nerve volley with a latency of about 10 ms and a duration of about 300 ms. This phenomenon has not been reported previously, so far as we are aware. We conclude that the retina, which originates from the forebrain of the developing embryo, behaves like a typical brain structure: it translates, within a few hundred milliseconds, the chemical information in each pattern of bleached photoreceptors into a corresponding pattern of ganglion cell neuronal information that leaves via the optic nerve. The attributes of each rat ganglion cell appear to include whether the retinal neuropile calls on it to leave after a stimulus and, if so when, within a 300-ms poststimulus epoch. The resulting retinal analysis of the scene, on arrival at the cortical level, is presumed to participate importantly in the creation of visual perceptual experiences.retinal ganglion cells ͉ optic chiasm ͉ visual perception V isual stimuli normally activate the entire retina, as when one drives an automobile or reads text like this. In such situations, saccadic eye movements jerk the eyeballs from one place to the next, coming to rest several times a second with the scene in focus on the retinal surface. To gain further insights into how information is transferred from retina to brain in such situations, we have been studying behaving rats with light-emitting diodes (LED) attached to the skull and electrodes implanted at the anatomical beginning, middle, and end of the visual system. Flashes of light from the LED, which appear to activate the entire retina (1), are varied in duration to simulate natural exposures such as a lightning flash, or the fixation at the end of a saccade, or an attempt to stare at an object without moving the eyes. We present here four simple experiments in which changes in stimulus parameters are correlated with the responses produced throughout the system.Readers will find the data presented here to be only distantly related to the mainstream of current electrophysiological research on animal visual systems. We are not interested in the activities of individual cells in the retinal, thalamic, or cortical neuropiles. We describe instead the activities recordable by large electrodes at three major stations of the system. We emphasize here the retinal neuronal output. We report that ganglion cell axons invariably leave the eyeball in a rigidly predetermined order during about 300 ms, even when the stimuli are delivered at a rate of three Hz. We interpret the data to mean that retinas normally cr...

Recordings were obtained from the visual system of rats as they cycled normally between waking (W), slow-wave sleep (SWS), and rapid eye movement (REM) sleep. Responses to flashes delivered by a light-emitting diode attached permanently to the skull were recorded through electrodes implanted on the cornea, in the chiasm, and on the cortex. The chiasm response reveals the temporal order in which the activated ganglion cell population exits the eyeball; as reported, this triphasic event is invariably short in latency (5-10 ms) and around 300 ms in duration, called the histogram. Here we describe the differences in the histograms recorded during W, SWS, and REM. SWS histograms are always larger than W histograms, and an REM histogram can resemble either. In other words, the optic nerve response to a given stimulus is labile; its configuration depends on whether the rat is asleep or awake. We link this physiological information with the anatomical fact that the brain dorsal raphe region, which is known to have a sleep regulatory role, sends fibers to the rat retina and receives fibers from it. At the cortical electrode, the visual cortical response amplitudes also vary, being largest during SWS. This well known phenomenon often is explained by changes taking place at the thalamic level. However, in the rat, the labile cortical response covaries with the labile optic nerve response, which suggests the cortical response enhancement during SWS is determined more by what happens in the retina than by what happens in the thalamus.optic chiasm ͉ 5-HT ͉ efferent retinal innervation W e have been studying the visual system of normal, behaving rats stimulated by a light-emitting diode (LED) permanently attached to the skull (1, 2). The red LED flashes activate the entire retina from behind the eyeball and evoke responses at electrodes implanted on the corneal surface of the eye, in the optic chiasm, and at the cortical terminal of the pathway. The overall objective is to describe the ganglion cell volley the retina creates as it converts rod͞cone photochemical information into its neuronal equivalents and to follow that neuronal activity as it moves past the chiasm electrode en route, mainly, to the lateral geniculate nucleus (LGN) and the cortex beyond.We have reported already that optic nerve axons exit the eyeball in a rigidly prescribed order for about 300 ms after stimulus onset (1). These ganglion cell volleys, called A͞B͞C͞histograms ¶ because of their triphasic waveform, are the inevitable product of rat retinas excited by full-field stimuli, and, we have argued, of human retinas as well. Here we compare the histograms of sleeping and waking (W) rats, show they are labile, and conclude that optic nerve modulation probably is controlled by the serotonin fibers known to reach the retina from the midbrain dorsal raphe nuclei. Finally, we show that the well known cortical response enhancement during SWS is the approximate mirror image of the enhanced ganglion cell histogram, and we discuss the significance of this fact. ...