[Sound affects the discrimination of weak intensities of light in the visual cortex of the rabbit depending on time intervals between sound and light].

In this paper, we researched an influence of sound (2000 Hz, 70 dB, 40 ms) to the discrimination of low-light intensities (0.3 and 1 cd/m2) in the visual cortex of the rabbit. We used a recording of evoked potentials from the visual cortex of awaked rabbits in chronic experiments. The sound was switched on with different time slots before and after the replacement of the light intensities at each other (range from -750 to +150 ms). Sound itself caused no response. In 42 experiments on 3 rabbits we revealed that' he sound has a significant modulating effect on the discrimination of low-light intensities in the range of time shifts from -300 to +50 ms. Maximum sound effect was manifested in the transition of light from a high-intensity (1 cd/m2) to lower (0.3 cd/m2). Analyses of the phases of visual evoked potentials revealed that significant influence of sound to the light occurs in the intervals -300, -100, -60, -40, -20, 0, -20 and + 50 ms. We found that phase P2 (120-150 ms from the moment of replacement of the light stimuli) is most affected by sound in response to the replacement of low-light intensities both in the number of significant (p < 0.05) time slots (7) and the impact of sound on the light response. In phase P2 the impact of sound was almost exclusively facilitating (by 19-36%) compared with the responses to the light, whereas in phases N1 80-110 ms) and N2 (180-250 ms) were only 2-3 intervals with the significant influence of the sound. And the degree of response facilitation to light was ranged by 8-12%. We assumed that the effect of sound on the light response in visual cortex is delayed that caused by the passage of auditory signal through the auditory,parietal cortex, superior colliculus.