Visual stimuli elicit action potentials in tens of different retinal ganglion cells.
Transforming the ‘highdimensional’ input into a temporal neural code, Each ganglion cell type responds with another latency to a given stimulus. The timing of the first spikes between different retinal projection neurons cells may further change along axonal transmission. The purpose of this study is to investigate if intraretinal conduction velocity leads to a synchronization or dispersion of the population signal leaving the eye. You should take it into account. We ‘imaged’ the initiation and transmission of lightevoked action potentials along individual axons in the rabbit retina at micron scale resolution using a highdensity ‘multitransistor’ array. We measured unimodal conduction velocity distributions for axonal populations whatsoever retinal eccentricities with the exception of the central part that contains myelinated axons. The velocity variance within any piece of retina is caused by ganglion cell types that show narrower and slightly different average velocity tuning. Ganglion cells of identical type respond with similar latency to spatially homogenous stimuli and conduct with similar velocity. While indicating that differences in first spike timing increase, For ganglion cells of different type intraretinal conduction velocity and response latency to flashed stimuli are negatively correlated. Similarly, the analysis of ‘pairwise’ correlated activity in response to white noise stimuli reveals that conduction velocity and response latency are negatively correlated.
Intraretinal conduction does not change the relative spike timing between ganglion cells of identical type but increases spike timing differences among ganglion cells of different type. The fastest retinal ganglion cells therefore act as indicators of new stimuli for postsynaptic neurons. The intraretinal dispersion of the population activity won’t be compensated by variability in extraretinal conduction times, estimated from data in the literature. Visual information is transmitted from the eye to the brain in trains of action potentials originating from populations of projection neurons, the retinal ganglion cells. Each ganglion cell type may respond with another latency to quite similar stimulus because of its presynaptic circuitry that is shaped by specific kinds of interneurons types,.
If the brain uses the information of different response latencies it requires the knowledge about stimulus onset. Alternatively, the first spikes in the population response may act as a ‘visual switch’ providing an internal reference for stimulus onset. Spike latencies referenced to stimulus onset carry information additional to that encoded by the spike rate as demonstrated in different sensory modalities, including visual,, somatosensory, and auditory systems,. ‘time lagged’ correlations between retinal ganglion cells facilitate rapid stimulus encoding, that can be used by animals in stimulus discrimination tasks. Needless to say, these studies exemplify the impact of spike timing in a neuronal population. With all that said… Latencies or relative time differences in the abovementioned studies were measured at the sites of signal initiation, close to the cell somata.
The response latency referenced to stimulus onset changes through axonal conduction in the retina and in the optic nerve. Action potentials originating from the peripheral retina propagate through unmyelinated axons along tens of millimeters in humans and many mammalian species until leaving the eye. Usually, ganglion cell type specific conduction velocity may contribute to spike timing differences. Based on antidromic electrical stimulation early studies in the cat suggest that X and Ycell axons conduct at different velocities within the retina,. The distinction between X and Y cells is prominent in the myelinated optic nerve, where Bishop and coworkers established the separation of the rapidly and slowly conducting axons. Anyways, thus, the optic nerve should be another source of temporal dispersion among action potentials.
In this study we investigated how intraretinal conduction in the rabbit retina changes the relative timing among spikes from different ganglion cells.
We ‘imaged’ the initiation of lightevoked action potentials and their orthodromic propagation along intraretinal axons using a multitransistor array, that provides high spatial and temporal sampling. You see, we relate the intraretinal conduction time for different ganglion cells to their response latency after flashed stimuli. Nonetheless, finally we discuss the effect of extraretinal conduction variability depending on published data,,,. In this study we investigated how intraretinal conduction in the rabbit retina changes the relative timing among spikes from different ganglion cells. We ‘imaged’ the initiation of lightevoked action potentials and their orthodromic propagation along intraretinal axons using a multitransistor array, that provides high spatial and temporal sampling. We relate the intraretinal conduction time for different ganglion cells to their response latency after flashed stimuli. Finally we discuss the effect of extraretinal conduction variability depending on published data,,,.