Abstract
Purpose :
This study examines how light-level history affects the encoding of natural images in the primate retina. We aim to determine how adaptation varies across different pathways, particularly in terms of time scales of adaptation. By investigating both the mechanistic and functional aspects of light adaptation in the context of natural stimuli, we aim to provide a more comprehensive picture of retinal processing and adaptation.
Methods :
We used a combination of single-cell patch-clamp and multi-electrode array (MEA) population recordings to assess the mechanistic and functional aspects of light adaptation. We focused on midget and parasol RGCs.
Results :
We measured responses to the same natural movie at the same mean light intensity (1 R*/rod/sec) following adaptation to different backgrounds (0.1 or 10 R*/rod/sec). The dependence of the responses on the adapting background persisted for many seconds following the change in light level. Further, the timescale over which this history dependence was lost differed substantially between parasol and midget RGCs (Fig 1B).
To investigate the origin of these differences, we measured responses to a temporal Gaussian noise stimulus that switched from 1 to 10 R*/rod/sec each minute (Fig 2A) and constructed LN models in several temporal windows following light intensity change (Fig 2B). Temporal filters changed quickly in both cell types following a change in intensity. Nonlinearities, however, changed more slowly in midget RGCs (~40s) compared to parasol RGCs (~5-10s). These differences in adaptation time scales were also evident in the excitatory inputs, indicating an origin in upstream retinal circuits. MEA recordings confirmed that these distinctions are reflected at the population level in simultaneously recorded cells.
Conclusions :
Our data reveal pathway-specific adaptational mechanisms that shape the dependence of midget and parasol RGC responses to stimulus history. The distinct light adaptation characteristics of midget cells identified here could potentially serve as a non-invasive tool to selectively 'silence' or reduce the influence of the midget pathway, offering a new avenue for understanding these pathways' roles in visual processing.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.