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Bruno Gomes, Givago Souza, Manoel Filho, Gobinda Pangeni, Luiz Carlos Silveira, Jan Kremers; The Spatial Distribution of L- and M-Cone Driven ERGs Reflecting Parvo- and Magnocellular Activity. Invest. Ophthalmol. Vis. Sci. 2013;54(15):6123.
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© ARVO (1962-2015); The Authors (2016-present)
To study the spatial distribution of the responses to L- and M-cone isolating stimuli at two different temporal frequencies: 36 Hz (where the ERGs presumably reflect magnocellular activity) and 12 Hz (where they reflect parvocellular activity).
A four primary LED Ganzfeld stimulator was used to create L- and M-cone isolating sinusoidal stimuli (each at 18 % cone contrast) by silencing the three other photoreceptor types using the silent substitution technique. The mean luminance was 284 cd/m2 (80, 160, 40 and 4 cd/m2 mean luminance of the red, orange, green and blue LEDs respectively). For full field (FF) stimulation the subjects rested their head inside the stimulator. For other stimulus sizes, the chin rest was located about 3 cm outside the stimulator. The appropriate stimulus sizes were created using cardboard field-stops. The following stimulus diameters were used: FF, 10° - 70° in 10° steps. In addition, 70° stimuli with 10° - 60° (in 10° steps) in the center ablated.
At 12 Hz, the amplitudes and phases of both L- and M-cone driven responses depended on stimulus size. However, L-/M-amplitude ratio was constantly around unity and the phase difference was close to 180°. At 36 Hz, the amplitudes of L- and M-cone driven responses depended differently on stimulus size. As a result, the L-/M-ratio depended on stimulus size: they were generally larger than one and increased with increasing stimulus size. Particularly with FF, L-cone driven responses were large and were on average about 5.5 times larger than FF M-cone driven responses and about three times larger than L-cone driven responses at 70° diameter. The phase difference between L- and M-cone driven responses did not depend on stimulus size but was not 180°.
The data suggest that the mechanisms underlying the ERG responses at 12 and 36 Hz (putatively the parvo- and magnocellular pathways) have different spatial properties.
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