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Avinash J Aher, Mellina M Jacob, Jan J Kremers; Spatial Properties of Electroretinograms Elicited by High Temporal Frequency L- and M-cone Isolating Stimuli. Invest. Ophthalmol. Vis. Sci. 2019;60(9):2506.
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© ARVO (1962-2015); The Authors (2016-present)
The aim of this study was to investigate the high temporal frequency characteristics of L- and M-cone isolating electroretinograms and the dependency of these characteristics on stimulus size.
The silent substitution stimulation technique was used to isolate L- and M-cone driven electroretinograms (ERGs). Two experiments were performed. In experiment 1 (4 subs; age: 31-58 yrs), the ERG responses elicited by the L- and M-cone isolating stimuli were recorded for 5 spatial stimulus configurations (full field and 70, 50, 30, and 10 deg diameter stimuli) each at 12 temporal frequencies (TF) (26 Hz to 48 Hz in the step of 2 Hz). In experiment 2 (3 subs; age: 28-58 yrs), the L- and M-cone driven ERG responses were measured only with full field and 70 deg stimuli but the frequency range was extended: 30 TFs between 26 Hz and 95 Hz were employed (from 26 Hz to 80 Hz in steps of 2 Hz, except 50 Hz, and from 80 Hz to 95 Hz in steps of 5 Hz). The L- and M-cone modulation contrasts were 10% in experiment 1 and 18% in experiment 2. The mean luminance in the two experiments was 284 cd/m2.
Responses to L- and M-cone isolating full field stimuli were maximal around 48 Hz and decreased gradually with increasing TF up to 95 Hz. The response maximum was decreased to about 30 - 32 Hz for both L- and M-cone driven responses obtained with spatially restricted stimuli. The M-cone driven responses could only be measured up to 54 Hz with 70 deg stimuli. The response amplitudes for L- and M-cones and L-/M-cone amplitude ratios decreased with decreasing stimulus size. The ERG response phases to L- and M-cone isolating stimuli decreased with increasing TF. The phase difference between L- and M-cone driven ERGs was about 160 deg for all stimulus sizes and frequencies up to 34 Hz. A further increase in the TF resulted in a decrease in L-M phase difference.
The data indicate that the responses evoked by high TF cone isolating stimuli reflect two mechanisms, one that is more centrally located and displays a maximum at about 30 - 32 Hz and a peripheral mechanism that is sensitive to higher temporal modulations. We propose that the peripheral mechanism (FF ERGs) reflects magnocellular activity, whereas the central mechanism (ERGs with spatially restricted stimuli) may be based on a parvocellular activity up to about 30 Hz.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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