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R. De Los Santos, B. Da Rocha Lima, L.M. Ventura, V. Porciatti; Physiological Fluctuations of Pattern Electroretinogram Associated With Presentation of Steady–State Pattern Stimuli . Invest. Ophthalmol. Vis. Sci. 2006;47(13):4012.
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© ARVO (1962-2015); The Authors (2016-present)
Electrical activity of single neurons in response to repeated presentation of visual stimuli typically shows fluctuations of amplitude/latency and habituation, whose extent may also depend on the pathophysiological conditions of the activated neurons. Standard response averaging necessary to improve the signal–to–noise ratio of Evoked Potentials precludes measurement of these potentially important dynamic changes. Our purpose is to evaluate physiological fluctuations of retinal ganglion cell (RGC) activity by means of a modified protocol of the Pattern Electroretinogram (PERG).
We used a specific running–average protocol for PERG recording (Porciatti et al IOVS 2005). A steady–state response was recorded simultaneously from both eyes of 21 normal subjects (mean age 41.9 ± 16 years) by means of skin electrodes on the lower eyelids. Visual stimuli were continuously presented for 5 minutes, and averaged in successive packets of 15 sec each. During the first minute, subjects viewed a uniform gray field (noise packets), and during the following 4 minutes a grating pattern of high–contrast (95%) reversing 16.6 times/s (PERG packets). We measured 1) the fluctuation (SD) of amplitude of the packets during the blank and the pattern presentation, 2) the progressive changes in amplitude of PERG packets with time. PERG packets were fitted with an exponential decay function, whose parameters were used to calculate a ratio R between the initial and final amplitude.
In agreement with previous results, PERG showed response habituation (mean R = 1.2 ± 0.34). The SD of PERG packets was larger than that of the noise by a factor of about 3 (PERG SD = 0.13 ± 0.05 µV; Noise SD = 0.05 ± 0.03 µV, P<0.001). The effect was not dependent on the absolute level of the signal, nor was related to changes in the quality of fixation during the recording time.
Electrical activity of RGCs in response to continuous presentation of patterned stimuli is associated with physiological fluctuations and habituation. These response properties can be reliably and non–invasively measured with a specific PERG protocol, and may provide potentially important markers of abnormal RGC activity.
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