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EE Sutter; Effects Of Feed Forward And Feedback Mechanisms In The Human Retina Revealed By The Multifocal Erg . Invest. Ophthalmol. Vis. Sci. 2002;43(13):1797.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To study the effects of fast adaptive mechanisms in the inner retina on the multifocal ERG (mfERG). Methods: The binary kernel series of the mfERG contains detailed information on the highly nonlinear local dynamics of retinal processing. However, the direct interpretation of the kernel series is difficult. The synthesis of response sequences from the kernels leads to a more intuitive representation of the same data. From a single record we learn how focal flash responses affect responses to subsequent stimuli and how they interfere with the generation of responses to preceding stimuli. A function of VERISTM 5 was used to synthesize and compare response sequences from the kernel series. Controls: To validate the synthesis procedure, results were spot-checked against with experiments using the actual corresponding stimulation sequences. Results: When computing the difference between focal flash responses in the presence and absence of a second flash following after 10 to 20 ms, one might expect response cancellation such that only the contribution from the second flash response remains. It turns out however, that the remaining response still contains a contribution that must be attributed to the preceding response. This contribution consists of a pronounced negativity that, in shape and timing, matches the inverted b-wave peak of the preceding response. Records derived at different stimulation rates confirm that this feature is time-locked with the preceding stimulus. This lack of response cancellation is consistent with a strong suppression of a b-wave component (second b-wave peak) by the following response. This phenomenon does not violate causality, since the second stimulus is presented before the b-wave of the preceding response is formed. As there are well-known feedback mechanisms in the retina it is possible that a response can also interfere with the development of a response to a preceding stimulus. Conclusion: The nonlinear analysis of the mfERG reveals that focal ERG responses can affect responses to preceding as well as following stimuli. These effects may be related to backward masking in visual perception. As the effects of a response on the b-wave of the preceding response are superimposed on the initial portion of the first order kernel, previous reports that glaucoma can affects the a-wave of the mfERG must be reconsidered.
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