Information in the Retina and Experiments on Photon Counting

There are mainly two parts in my presentation this time, results and analysis for the omitted stimulus response (OSR) experiment with spatial stimuli and some preliminary tests for photon counting in retina.

Last time, I talked about a hypothesized simple columnar organization that produces OSR in the retina. We may investigate the circuits by providing light stimuli with spatial patterns. Uniform, checkerboard, and random distributed pixels were used as the periodic stimulus. Fixing the number of flashes, period, and the average brightness, we see that OSR can only be generated under uniform, checkerboard or fixed random pixels (that are unchanged within a trial), but not in the anti-checkerboard or random pixel stimuli (that changes in every flashes). This implies that there may be specific spatial units to produce OSR. Further investigation is needed to identify the size and properties of these units.

In addition, I calculated spatial correlation and temporal information from the spike trains in previous experiments. For spatial correlation, we find that the correlated distance is longer under uniform stimuli than random flickers or checkerboard. Interestingly, those producing OSR seem to also have shorter correlation distance than those that simply response to each light flashes. For temporal information, my extrapolation results seem to provide less entropy rate comparing to the previous researches. I might find another method that fits our experiment better to calculate temporal information. Lastly, I’ve been reading articles focusing on the strong inhibitions in the retina. The inhibitory signal may not only play an important role in the anti-Hebbian model but also help encoding information through silencing neighbor neurons. Since we've been recently discussing the strong inhibition right after OSR, I'm also interested in how OSR affects the synergitic codes in retina.

For photon counting on the retina, I briefly went through some classic experiments showing the single photon sensitivity and detection of photon statistics in photoreceptor cells. Most researches focus on the gain control and regulation of threshold in the retina under dim light. In the future, we hope to calculate the correlation between spikes from ganglion cells, which really send information to the brain, to investigate whether photon information could still preserve after processing through the retinal circuits. 

Comments

Thanks for the interesting results. In your OSR for patterned stimulus, how does the size of checker board cells compare with the "pixels" of random pattern? Also, to the size of receptive field or the pitch of MEA?

The diameter of receptive fields in retina are 200-300 micrometers in average according to the references, and the distance between electrodes of our 8X8 MEA is 200 micormeters. For the 'pixels' I mentioned in the slides, their size are identical to the checkerboard cells, which is around 60 microumeters. I'll try to change the size of these pixels in the following experimetns.

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