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Mineo Kondo, Paul A. Sieving; Primate Photopic Sine-Wave Flicker ERG: Vector Modeling Analysis of Component Origins Using Glutamate Analogs. Invest. Ophthalmol. Vis. Sci. 2001;42(1):305-312.
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purpose. To study how the photoreceptoral and postreceptoral ON- and
OFF-components contribute to the photopic sine-wave flicker ERG in the
monkey by isolating the components with glutamate analogs.
methods. Monkey photopic flicker ERGs were elicited with sine wave stimuli (mean
luminance, 2.66 log cd/m2; 80% modulation depth, on a 40
cd/m2 white background) and were recorded for stimulus
frequencies of 4 Hz to 64 Hz, before and after intravitreal injection
of dl-2-amino-4-phosphonobutyric acid (APB) and cis-2,3-piperidinedicarboxylic acid (PDA) that block ON-
and OFF-bipolar activity, respectively. The amplitude and phase of the
fundamental component were analyzed.
results. The flicker response amplitudes increased after APB, for frequencies of
6 Hz to 32 Hz. The further addition of PDA to isolate the photoreceptor
component resulted in a relatively small residual response that
decreased monotonically from 4 Hz to 32 Hz. The postsynaptic APB (ON-)
and PDA (OFF-) sensitive components were isolated by subtraction and
were characterized by amplitude and phase vectors. The ON- and
OFF-components were larger than the initial control responses for
stimuli of 8 Hz to 40 Hz. These two components had a
frequency-dependent phase difference of 160° to 230°; normally,
they interfere with each other and reduce their net contribution. The
phase difference between ON- and OFF-components was nearly 180° for a
10-Hz stimulus, and the phase cancellation caused a prominent dip in
amplitude at this frequency.
conclusions. These results indicate that postreceptoral ON- and OFF-components
contribute substantially to the sine-wave flicker ERG, especially at
higher stimulus frequencies. Because of phase cancellation, they mask
each other in the net response in a frequency dependent fashion. The
photoreceptor contribution is greater than the net postsynaptic
component only for frequencies of approximately less than or equal to
10 Hz. These results can be summarized by a vector model that may be
useful for interpreting changes resulting from retinal
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