Abstract
Purpose :
Retinal adaptation involves various mechanisms operating across a wide range of temporal and spatial scales to mediate many functional changes. These include gain control mechanisms that adjust retinal sensitivity and mechanisms that alter the stimulus features that the retina encodes. It is unclear how these processes alter computations performed by retinal cells during dynamic natural stimuli. We tested whether light-level-dependent changes in retinal ganglion cell (RGC) responses to natural stimuli could be explained by global or local stimulus features.
Methods :
We recorded from a population of ON (N=27) and OFF (N=23) primate parasol RGCs using a multi-electrode array. Natural movies generated from the Database of Visual Eye Movements (van der Linde, I. 2009) at 0.5 (scotopic) and 50 (mesopic) R*/rod/s were repeated 9 times and responses averaged using a bin rate of 60Hz. The resulting peristimulus time histograms (PSTHs) were used to determine how responses to the same movie in the same RGC differed across light levels. Initial analyses focused on transfer functions that converted a cell’s mesopic PSTH to its scotopic PSTH. We tested how well transfer functions for one cell and one movie generalized across cells for the same movie or across movies in the same cell. We quantified generalization using the Pearson’s correlation between predicted and observed PSTH.
Results :
As expected, responses slowed as light level decreased, and responses of nearby cells were more similar than those of distant cells. In addition to expected changes, two observations indicated that changes in coding depended on local stimulus structure. First, we found that the ability of mesopic-to-scotopic transfer functions to generalize across cells depended on the distance between cell receptive fields (ON: R=-0.44 +/- 0.0074, p<0.001; OFF: R= -0.49 +/- 0.0093, p<0.001) and on the correlation of average pixel intensity of cell receptive fields (ON: R=0.39 +/- 0.011, p<0.001; OFF: R=0.47 +/- 0.011, p<0.001). Second, transfer functions did not generalize across stimuli within the same cell (ON: R=0.031 +/- 0.0054, p<0.001 OFF: R=-0.0052 +/- 0.0049, p=0.29). Results presented as mean +/- standard error.
Conclusions :
Our results suggest that local stimulus features contribute to the temporal and kinetic changes in RGC responses that occur on the timescale of saccades.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.