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Interaction between center and surround in rabbit retinal ganglion cells
D K Merwine1, F R Amthor, N M Grzywacz
1Department of Physiological Optics, School of Optometry, University of Alabama at Birmingham 35294, USA.
This study explored how the center and surround regions of retinal ganglion cells interact in rabbits. Using recordings from isolated eyes, researchers found that stimulation of the surround area primarily reduces the strength of responses in the center region. This effect was consistent across different types of ganglion cells. The timing of surround stimulation matters: it is most effective when it happens at the same time as center stimulation. If the surround is stimulated too early, its inhibitory effect weakens. The study also found that this effect is not due to simple changes in brightness. Instead, the surround's influence extends into the center region itself, suggesting a complex interaction. These findings help clarify how retinal circuits process visual information.
Area of Science:
- Visual neuroscience
- Retinal physiology
- Sensory processing
Background:
Understanding how retinal ganglion cells process visual information remains a central challenge in sensory neuroscience. Prior research has shown that these cells integrate signals from multiple regions of their receptive fields. However, the specific nature of interactions between central and surrounding areas is less clear. Earlier studies have demonstrated that ganglion cells respond to contrast in a nonlinear fashion. Yet, the exact mechanisms by which surround stimulation modulates center responses remain uncertain. This uncertainty drives the need for detailed investigations into the functional properties of retinal ganglion cells. No prior work had resolved how temporal and spatial factors influence these interactions. The gap motivated the current study to examine these interactions across multiple ganglion cell classes. This paper's contribution lies in its systematic analysis of center-surround dynamics using extracellular recordings. The study's findings may clarify how retinal circuits process visual stimuli.
Purpose Of The Study:
This study aimed to investigate how center and surround mechanisms interact in retinal ganglion cells of the rabbit. The researchers focused on various ganglion cell classes, including on and off brisk sustained and transient types. They sought to determine how surround stimulation affects center responses across different cell types. The motivation stemmed from the need to understand how retinal circuits process visual contrast. The study also aimed to assess the temporal dynamics of surround effects. By examining step changes in surround contrast, the researchers intended to measure response delays. The work sought to clarify whether surround effects are due to luminance adaptation or other mechanisms. This approach allowed for a detailed characterization of center-surround interactions.
Main Methods:
The researchers used extracellular single-unit recordings in an isolated eyecup preparation. They examined a range of rabbit retinal ganglion cell classes, including on and off brisk sustained and transient types. The study involved measuring response-versus-contrast functions for stimuli within the receptive-field centers. Surround effects were assessed by varying the timing and contrast of annular stimuli. Step changes in surround contrast were synchronized with center stimulation. The researchers also used sine-wave gratings to test spatial frequency effects. They analyzed how surround stimulation affected the slope of center response curves. The methods allowed for a detailed temporal and spatial analysis of center-surround interactions.
Main Results:
The study found that surround stimulation primarily reduced the slope of center response-versus-contrast functions. This effect was consistent across all ganglion cell classes examined. The contrast threshold for the center spot was not significantly affected by surround stimulation. When threshold changes occurred, they sometimes decreased rather than increased. Surround inhibition was most effective when stimulation was simultaneous with the center. Inhibition decreased significantly when surround stimulation preceded the center by more than 100 ms. The inhibitory effect was generally ineffective when the delay exceeded 500 ms. The decrease in inhibition was a monotonic function of delay between 0 and 500 ms.
Conclusions:
The authors concluded that surround effects primarily modulate the slope of center responses rather than their threshold. This modulation was consistent across multiple ganglion cell classes. The inhibitory effect was most pronounced when surround and center stimulation were simultaneous. The study found that surround inhibition decreased with increasing delay. The inhibitory effect was also influenced by spatial frequency in sine-wave gratings. The results suggest that surround inhibition extends into the receptive-field center. The findings do not support pure luminance adaptation as the sole mechanism. The authors propose that these interactions reflect a broader functional property of retinal ganglion cells.
Frequently Asked Questions
Surround stimulation primarily reduces the slope of the center's response-versus-contrast function, rather than shifting the threshold.
The inhibitory effect is strongest when surround and center stimulation are simultaneous. It decreases significantly when the delay exceeds 100 ms.
Sine-wave gratings were used to test whether surround effects were due to luminance adaptation or other mechanisms.
It suggests that surround inhibition extends into the receptive-field center, affecting responses to stimuli within the excitatory region.
They measured changes in the slope of the response-versus-contrast function for center stimuli under varying surround conditions.
The findings suggest that surround inhibition modulates center responses in a consistent manner across ganglion cell types.