Abstract
The information regarding visual stimulus is encoded in spike trains at the output of retina by retinal ganglion cells (RGCs). Among these, the directional selective cells (DSRGC) are signaling the direction of stimulus motion. DSRGCs' spike trains show accentuated periods of short interspike intervals (ISIs) framed by periods of isolated spikes. Here we use two types of visual stimulus, white noise and drifting bars, and show that short ISI spikes of DSRGCs spike trains are more often correlated to their preferred stimulus feature (that is, the direction of stimulus motion) and carry more information than longer ISI spikes. Firstly, our results show that correlation between stimulus and recorded neuronal response is best at short ISI spiking activity and decrease as ISI becomes larger. We then used grating bars stimulus and found that as ISI becomes shorter the directional selectivity is better and information rates are higher. Interestingly, for the less encountered type of DSRGC, known as ON-DSRGC, short ISI distribution and information rates revealed consistent differences when compared with the other directional selective cell type, the ON-OFF DSRGC. However, these findings suggest that ISI-based temporal filtering integrates a mechanism for visual information processing at the output of retina toward higher stages within early visual system.
Highlights
The information regarding visual stimulus is encapsulated initially in spike trains at the output of retina by retinal ganglion cells [1,2,3,4]
We focused on the optimal stimulus feature as being the stimulus direction of motion and analyzed the response of directional selective retinal ganglion cells (DSRGCs) to the visual stimulus consisting in drifting grating bars, a commonly used stimulus to quantify the direction selectivity [4, 7, 30]
Scanning the spike trains of each retinal ganglion cell in response to the stimulus applied, we found that for all of the cells most of the spikes were preceded by short time intervals; that is, the activity with short interspike intervals (ISIs) was predominant
Summary
The information regarding visual stimulus is encapsulated initially in spike trains at the output of retina by retinal ganglion cells [1,2,3,4]. For the LGN cells the center-surround RFs are similar to those of retinal afferents [14,15,16] With this advantage in mind, together with the fact that the receptive field centers of LGN cells receive their main input from only one retinal ganglion cell (RGC) [17,18,19], the retinogeniculate synapse represents a major interest for studying the role of interspike interval-based mechanism for spike filtering and visual information processing [3, 20,21,22,23]. Already at the stage within early visual system, neurons in layer 4 of primary visual cortex receive many more convergent inputs from LGN counterparts [16] and rely more on the interaction between different inputs than on the interspike intervals (ISIs) of individual inputs as part of the mechanism to reach the spike threshold [24]
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