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G. Pangeni, J. Kremers; A New Interpretation of Components in the Erg Signals to Sine Wave Luminance Stimuli at Different Temporal Frequencies and Contrasts. Invest. Ophthalmol. Vis. Sci. 2010;51(13):1490.
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© ARVO (1962-2015); The Authors (2016-present)
To describe constituent components in the full-field luminance flicker ERGs in normal human subjects using a novel analysis.
Full-field stimuli were produced using a ganzfeld bowl with arrays of Light Emitting Diodes (LEDs) as light sources. ERG responses were recorded using DTL electrodes from five subjects (mean age ± SD: 34.4 ± 8.8) using luminance sine wave stimuli (white light; mean luminance 250cd/m²) at different frequencies (1-120 Hz) and contrasts (25-100%). Signal analysis was performed using self-written programmes and spreadsheets in MATLAB and Excel.
In agreement with previous studies, Fourier analysis on the original responses revealed that the amplitude of the fundamental component displayed a dip at about 12 Hz, coinciding with a maximum in the second harmonic component, indicating frequency doubled responses. By including measurements at low contrasts, it was possible to identify two distinct components. We introduced a new analysis method that separated the two components. We found that the waveform of a spike-like ("peaky") component was independent of frequency, but could vary in amplitude and time of occurrence. This component was fitted to the original response. Subtraction of the fitted "peaky" component from the original response revealed a second component with a waveform that closely resembled the waveform of the stimulus. This "sine-wave" component depends linearly on contrast and is prominent at low temporal frequencies, absent above 16 Hz and resembles the ERG in non-human primates after pharmacological blocking of signal transmission from photoreceptors to bipolar cells. The "peaky" component has a more non-linear contrast relationship and is more prominent in the high frequency region peaking at about 40 Hz. At about 12 Hz the two components have similar amplitudes.
We propose that the "sine-wave" component is mainly driven by activity of the photoreceptors (but does probably not reflect the modulation of the photoreceptor excitation) and the "peaky" component mainly represents activity of the inner retina. The interaction between these components at about 12 Hz results in a frequency doubled response.
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