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  • Title: [Differentiation of the bimodal stimuli in a frog's retina].
    Author: Izmaĭlov ChA, Zimachev MM.
    Journal: Zh Vyssh Nerv Deiat Im I P Pavlova; 2007; 57(1):65-79. PubMed ID: 17432319.
    Abstract:
    In work electric activity of frog's retina was investigated by silent substitution technique. Electroretinogram was recorded as a response to abrupt exchange of the referent stimulus-line with fixed values of luminance and orientation to test lines with varied luminance and orientations. As a result of the analysis it has been allocated two types of responses of a retina. The response to onset-offset of a stimulus-line was similar to the response at homogeneous illumination of a retina (ERG), and was characterized by both the high amplitude of b-wave (hundreds mkV) and significant asymmetry of b- and d-waves. Whereas the same waves in response to substitution of the same stimuli were more symmetric and had on ten times smaller amplitudes. Such activity of frog's retina was referred as pattern electroretinogram (PERG) recorded in a high vertebrate's retina as response to stimuli whose contrast was temporally modulated. The analysis of interaction of luminance and line orientation channels in retina was carried out on the base of construction V-shaped functions of stimuli differentiation. It has shown, that activities of both channels are linearly summarized in PERG. It means independent and parallel functioning of these mechanisms. However, it takes the short subdivision of luminance, namely, when luminance of test line not far from luminance of referent line. At the same time, from the moment of the double prevalence of test line in relation to referent line, growth of PERG amplitude has nonlinearly form. Such two-stage changing of PERG amplitude speaks presence in a retina of a frog of two mechanisms of coding of luminance. One mechanism coding light intensity by power of the discharge, it forms the information on an absolute level of light in the environment. Its activity is caused basically, by receptors and cells of external plexiform layer and is submitted by b-wave of electroretinogram. Other mechanism submitted in PERG, is based on the vector code of stimulus, it forms the information on spatial and time differentiation of a light in the visual field and is connected, basically, with cells of internal plexiform layer of frog's retina.
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