Extracellular recording of 34 neurons in the primary visual cortex of three conscious rabbits was performed in chronic experimental studies addressing the effects of sound (2000 Hz, 70 dB, 40 msec) on the discrimination of weak light intensities (0.3–1 cd/m2). Sound was delivered with different time intervals before and after substitution of one light intensity by another (using a total of 15 intervals in the range –750 to +150 msec). Factor analysis of variance (ANOVA) showed that the time interval between the sound and the light had statistically significant influences on neuron responses. Sound itself provoked no response. Neuron reactions consisted of responses to increases (on responses) and decreases (off responses) in light intensity. The most marked effect of sound was seen in the initial phase of the response (40–100 msec from the moment at which intensities were substituted). For every interval, neurons demonstrated both increases and decreases in reactions to complexes as compared with their responses to light. Wilcoxon’s T test was used to assess differences in sets of responses to light and to complexes. For the on responses of the whole group of neurons, the absolute values of responses to sound + light complexes were significantly (p < 0.05) different from responses to light (increased reactions) at intervals of –150, –40, and 0 msec. Two groups of neurons were identified, for which the effects of sound on responses to light were markedly different. Neurons of group 1 (n = 16) showed significant positive influences of light on on responses over a wide range of intervals (–150, –40, –20, 0, +20, +100 msec), along with a larger increase in the number of spikes due to sound (by 18–28%) as compared with responses to light. Neurons of group 2 (n = 18) had no significant intervals, i.e., at which reactions to complexes were not significantly different from responses to light. None of the study groups of neurons showed intervals with significant decreases in responses to complexes, though there was a tendency for reactions to complexes to shift towards weakening of responses at intervals of –750 and –80 msec for group 1 (p < 0.07) and at intervals of –500 and +20 sec for group 2 (p < 0.1). On responses were found to be more strongly affected by sound than off responses. The effects of sound on the second phases of responses to light (120–160 msec and later, n = 23) were also studied. Sound had markedly weaker effects on the second phase than the first. For the whole group of neurons with late phases, sound had significant influences on on responses with an interval of 0 msec and on off responses with intervals of +100 and +150 msec. Our study demonstrated similarity in the time intervals for modulation of reactions to light by sound in experiments on animals and psychophysical studies in humans. These data provide for more detailed studies of the integration of light and sound when used simultaneously.

Visual evoked potentials (VEP) recorded from the visual cortex of conscious rabbits in chronic experiments were used to study the effects of sound (2000 Hz, 70 dB, 40 msec) on the discrimination of low light intensities (0.3–1 cd/m2). Sounds were delivered with different time delays before and after replacement of one light intensity by another (range –750 to +150 msec). The sound itself did not induce any response. A total of 42 experiments on three rabbits showed that sound had a significant modulatory effect on the discrimination of low light intensities in the range of sound-light intervals from –300 to +50 msec. Sound had the strongest effect going from high light intensities (1 cd/m2) to low (0.3 cd/m2). Analysis of the phases of visual evoked potentials showed that sound had a significant influence on the light response at intervals of –300, –100, –60, –40, –20, 0, +20, and +50 msec. During the P2 phase (120–150 msec from the moment of light stimulus substitution), sound had its greatest influence on substitution of low light intensities both in terms of the number of time intervals (seven) at which the effect of sound was significant (p < 0.05) and in terms of the extent of the effect of sound on the light response. The effects of sound in the P2 phase were almost exclusively facilitatory – by 19–36% compared with responses to light, while the N1 (80–110 msec) and N2 (180–250 msec) phases included 2–3 intervals with significant sound effects, the extent of facilitation of the response to light varying over the range 8–12%. It is suggested that the action of sound on the light response over time is mediated in the visual cortex with some delay due to passage of the sound signal through the auditory cortex, parietal cortex, and superior colliculi.

). Звук подавался с разными временнми интервалами до и после замены одной интенсивности света на другую (всего 15 интервалов, диапазон от –750 до +150 мс). Факторный дисперсионный анализ ANOVA показал, что временнй интервал между звуком и светом статистически значимо влияет на ответы нейронов. Сам звук ответа не вызывал. Реакции нейронов содержали в себе ответы на увеличение (on-ответы) и на уменьшение (off-ответы) интенсивности света. Наиболее выражено влияние звука в начальной фазе ответа (40–100 мс от момента замены интенсивностей). Для каждого интервала нейроны демонстрировали как увеличение, так и уменьшение реакций на комплекс по сравнению с реакциями на свет. Был применен Т-критерий Вилкоксона для оценки различия в выборках ответов на свет и на комплекс. Для on-ответов всей группы нейронов абсолютные значения реакций на комплекс звука со светом значимо (p < 0.05) отличались от реакций на свет (в сторону усиления реакций) при интервалах –150, –40 и 0 мс. Выделены две группы нейронов, для которых влияние звука на световые ответы заметно различалось. Нейроны первой группы (n = 16) показали значимое положительное влияние звука на on-ответ в широком диапазоне интервалов (–150, –40, –20, 0, +20, +100 мс), а также наибольшее увеличение числа спайков под влиянием звука (на 18–28%) по сравнению с ответом на свет. У нейронов второй группы (n = 18) значимых интервалов обнаружено не было, т.е. реакции на комплекс не отличались значимо от ответов на свет. Для всех исследованных групп нейронов не обнаружено интервалов с достоверным снижением реакций на комплекс, однако наблюдалась тенденция сдвигов реакций на комплекс в сторону ослабления ответов при интервалах –750 и –80 мс для группы 1 (p < 0.07) и при интервалах –500 и +20 мс для группы 2 (p < 0.1). Установлено, что on-ответы сильнее подвержены действию звука, чем off-ответы. Исследовано также влияние звука на вторые фазы ответа на свет (120–160 мс и более поздние, n = 23). Здесь влияние звука заметно слабее, чем на первую фазу. Для всей группы нейронов с поздними фазами звук значимо влияет на on-ответы в интервале 0 мс, на off-ответы – в интервалах +100, +150 мс. Наша работа выявила сходство временнх интервалов модуляции звуком реакций на свет в опытах на животных и в психофизических опытах на людях. Полученные данные позволяют более подробно исследовать интеграцию звука и света при их совместном применении. ). Звук подавался с разными временнми интервалами до и после замены одной интенсивности света на другую (всего 15 интервалов, диапазон от –750 до +150 мс). Факторный дисперсионный анализ ANOVA показал, что временнй интервал между звуком и светом статистически значимо влияет на ответы нейронов. Сам звук ответа не вызывал. Реакции нейронов содержали в себе ответы на увеличение (on-ответы) и на уменьшение (off-ответы) интенсивности света. Наиболее выражено влияние звука в начальной фазе ответа (40–100 мс от момента замены интенсивностей). Для каждого интервала нейроны демонстрировали как увеличение, так и уменьшение реакций на комплекс по сравнению с реакциями на свет. Был применен Т-критерий Вилкоксона для оценки различия в выборках ответов на свет и на комплекс. Для on-ответов всей группы нейронов абсолютные значения реакций на комплекс звука со светом значимо (p < 0.05) отличались от реакций на свет (в сторону усиления реакций) при интервалах –150, –40 и 0 мс. Выделены две группы нейронов, для которых влияние звука на световые ответы заметно различалось. Нейроны первой группы (n = 16) показали значимое положительное влияние звука на on-ответ в широком диапазоне интервалов (–150, –40, –20, 0, +20, +100 мс), а также наибольшее увеличение числа спайков под влиянием звука (на 18–28%) по сравнению с ответом на свет. У нейронов второй группы (n = 18) значимых интервалов обнаружено не было, т.е. реакции на комплекс не отличались значимо от ответов на свет. Для всех исследованных групп нейронов не обнаружено интервалов с достоверным снижением реакций на комплекс, однако наблюдалась тенденция сдвигов реакций на комплекс в сторону ослабления ответов при интервалах –750 и –80 мс для группы 1 (p < 0.07) и при интервалах –500 и +20 мс для группы 2 (p < 0.1). Установлено, что on-ответы сильнее подвержены действию звука, чем off-ответы. Исследовано также влияние звука на вторые фазы ответа на свет (120–160 мс и более поздние, n = 23). Здесь влияние звука заметно слабее, чем на первую фазу. Для всей группы нейронов с поздними фазами звук значимо влияет на on-ответы в интервале 0 мс, на off-ответы – в интервалах +100, +150 мс. Наша работа выявила сходство временнх интервалов модуляции звуком реакций на свет в опытах на животных и в психофизических опытах на людях. Полученные данные позволяют более подробно исследовать интеграцию звука и света при их совместном применении. ). Звук подавался с разными временнми интервалами до и после замены одной интенсивности света на другую (всего 15 интервалов, диапазон от –750 до +150 мс). Факторный дисперсионный анализ ANOVA показал, что временнй интервал между звуком и светом статистически значимо влияет на ответы нейронов. Сам звук ответа не вызывал. Реакции нейронов содержали в себе ответы на увеличение (on-ответы) и на уменьшение (off-ответы) интенсивности света. Наиболее выражено влияние звука в начальной фазе ответа (40–100 мс от момента замены интенсивностей). Для каждого интервала нейроны демонстрировали как увеличение, так и уменьшение реакций на комплекс по сравнению с реакциями на свет. Был применен Т-критерий Вилкоксона для оценки различия в выборках ответов на свет и на комплекс. Для on-ответов всей группы нейронов абсолютные значения реакций на комплекс звука со светом значимо (p < 0.05) отличались от реакций на свет (в сторону усиления реакций) при интервалах –150, –40 и 0 мс. Выделены две группы нейронов, для которых влияние звука на световые ответы заметно различалось. Нейроны первой группы (n = 16) показали значимое положительное влияние звука на on-ответ в широком диапазоне интервалов (–150, –40, –20, 0, +20, +100 мс), а также наибольшее увеличение числа спайков под влиянием звука (на 18–28%) по сравнению с ответом на свет. У нейронов второй группы (n = 18) значимых интервалов обнаружено не было, т.е. реакции на комплекс не отличались значимо от ответов на свет. Для всех исследованных групп нейронов не обнаружено интервалов с достоверным снижением реакций на комплекс, однако наблюдалась тенденция сдвигов реакций на комплекс в сторону ослабления ответов при интервалах –750 и –80 мс для группы 1 (p < 0.07) и при интервалах –500 и +20 мс для группы 2 (p < 0.1). Установлено, что on-ответы сильнее подвержены действию звука, чем off-ответы. Исследовано также влияние звука на вторые фазы ответа на свет (120–160 мс и более поздние, n = 23). Здесь влияние звука заметно слабее, чем на первую фазу. Для всей группы нейронов с поздними фазами звук значимо влияет на on-ответы в интервале 0 мс, на off-ответы – в интервалах +100, +150 мс. Наша работа выявила сходство временнх интервалов модуляции звуком реакций на свет в опытах на животных и в психофизических опытах на людях. Полученные данные позволяют более подробно исследовать интеграцию звука и света при их совместном применении. х интервалов модуляции звуком реакций на свет в опытах на животных и в психофизических опытах на людях. Полученные данные позволяют более подробно исследовать интеграцию звука и света при их совместном применении.

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.

Electrodes were implanted into cranium above the primary visual cortex of four rabbits (Orictolagus cuniculus). At the first stage, visual evoked potentials (VEPs) were recorded in response to substitution of threshold visual stimuli (0.28 and 0.31 cd/m(2)). Then the sound (2000 Hz, 84 dB, duration 40 ms) was added simultaneously to every visual stimulus. Single sounds (without visual stimuli) did not produce a VEP-response. It was found that the amplitude of VEP component N1 (85-110 ms) in response to complex stimuli (visual and sound) increased 1.6 times as compared to "simple" visual stimulation. At the second stage, paired substitutions of 8 different visual stimuli (range 0.38-20.2 cd/m(2)) by each other were performed. Sensory spaces of intensity were reconstructed on the basis of factor analysis. Sensory spaces of complexes were reconstructed in a similar way for simultaneous visual and sound stimulation. Comparison of vectors representing the stimuli in the spaces showed that the addition of a sound led to a 1.4-fold expansion of the space occupied by smaller intensities (0.28; 1.02; 3.05; 6.35 cd/m(2)). Also, the addition of the sound led to an arrangement of intensities in an ascending order. At the same time, the sound 1.33-times narrowed the space of larger intensities (8.48; 13.7; 16.8; 20.2 cd/m(2)). It is suggested that the addition of a sound improves a distinction of smaller intensities and impairs a distinction of larger intensities. Sensory spaces revealed by complex stimuli were two-dimensional. This fact can be a consequence of integration of sound and light in a unified complex at simultaneous stimulation.

Changes in activity of 92 neurons in the primary visual cortex of four rabbits (Orictolagus cuniculus) were analyzed. In the first series of experiments, we recorded discharges of 63 neurons in response to replacement of visual stimuli in pairs (pairs of 0.28 - 1, 1 - 3, 3 - 6, 6 - 8.5, 8.5 - 14, 14 - 17, 17 - 20 cd/m2). Then the same stimuli were presented simultaneously with sound (70 dB, 2000 Hz, 40 ms). Neurons did not respond directly to the sound. Two groups of neurons were found. In the first group of neurons (31%), responses to the complex "light and sound" (40-100 ms from the moment of substitution of stimuli) increased on average by 41% (p < 0.0001) under conditions of the lowest stimuli intensities. With increasing light intensities, discharges to the complex were reduced to the background level of responses to light and even lower. The second group of neurons (19%) showed the opposite properties: at low intensities, responses to the complex were comparable to responses to light (or even lower). At high intensities (14-20 cd/m2), discharges to the complex were significantly (p < 0.05) different from the responses to light (20% and higher, up to 39%). In the second series of experiments, we reconstructed vector sensory spaces on the basis of responses of 29 neurons to light of different intensities and eight complexes of "light and sound." It was found that the sound had also a dual effect on the sensory space of complexes. Some neurons showed an enhancement of the angular distance between the two lowest light intensities (0.28 and 1 cd/m2). Other neurons showed an increase in the angular distance between the highest intensities. Such changes in the space structure are consistent with the groups of neurons revealed in the first two series of the experiments. Comparison of the dynamics of neuronal responses and the amplitudes of evoked potentials under the same conditions of stimulation revealed their considerable similarity. Thus, modulation of neuronal activity in the visual cortex by sound is a complex nonlinear process.

Changes in the number of spikes in the early phasic discharge (50-90 ms from stimuli replacement) of neurons in the rabbit's primary visual cortex were studied under conditions of an instant change in a flashing-line pattern. We used three type of stimulation: lines with different orientations (0-90 degrees) but constant intensity; lines with constant orientation but different intensities; complex stimuli with different intensities and different orientations of lines. Factor analysis made it possible to reconstruct two-dimensional sensory spaces of orientations in 13 of 43 analyzed neurons (30%). In 5 of 30 analyzed neurons (16.6%), both two-dimensional spaces of orientations and two-dimensional spaces of intensities were revealed. Achromatic spaces were reconstructed during changes in the lines of varying intensities but constant orientation. In experiments with complex stimuli, the intensity of lines with orientations varying from 0 to 38.58 degree was 5 cd/m2. The intensity of lines with orientations varying from 51.44 to 90 degrees was 15 cd/m2. In the sensorial space, stimuli with different intensities were located on the plane formed by the first and second significant factors in opposite quadrants, whereas within each quadrant, the stimuli were arranged closely to their orientation from minimum to maximum. We suggest that this type of sensory space reflects the interaction between intensity and orientation attributes of visual stimuli with the factor of intensity prevailing over the factor of orientation. Only 7 (12%) neurons with such complex spaces were found.

Changes in the amplitudes of evoked potentials in the visual cortex of conscious rabbits in response to substitution of flashing lines of different orientations (0–90°) but constant intensity were studied, along with interneurons of different intensities but constant orientation, and complex stimuli with simultaneous changes in flash orientation and intensity. Factor analysis of the results showed that analysis of the N85 peak of evoked potentials produced by substitution of stimuli with different orientations but constant intensity identified a two-dimensional sensory space for orientations. An achromatic sensory space was also detected using substitution of lines of different intensities but constant orientation. Substitution of complex stimuli involved two versions of the experiment. In the first version, four stimuli in the initial orientations (0–38.58°) had an intensity of 5 cd/m2, the other stimuli (with orientations of 51.44–90°) were presented at an intensity of 15 cd/m2. On the plane of the sensory space formed by the first two significant factors, stimuli with different intensities were located in different quadrants of the circle, while within the quadrants themselves, the stimuli were located in accord with their orientations, from lower values to greater. It is suggested that in this version, an interaction between orientation and intensity attributes was seen on the single plane of the sensory space, with a clear predominance of the intensity factor. The other experimental version also included eight complex stimuli, each complex having its own orientation (one of eight over the range 0–90°) and intensity (also one of eight, in the range 5–21 cd/m2). In all experiments involving substitution of complex stimuli, factor analysis identified three to four significant factors. In the vast majority of cases, only the sensory space plane X1, X2 was found, this being formed by two significant factors. On this plane, the stimuli were located in order of changes in intensity. This may be associated with the fact that rabbits are crepuscular animals, such that stimulus brightness is the most important attribute. However, in some cases, potentials in the rabbit brain also demonstrated simultaneous processing of two visual stimulus attributes, i.e., intensity and orientation. This may be evidence indicating analysis of complex stimuli in the primary visual cortex.

Amplitude variations of visual evoked potentials (VEP) in rabbit were studied using changes of three types of stimuli: lines with different orientations (0-90 degree) but constant in intensity, lines with different intensities but constant in orientation, and complex stimuli with different intensities and different orientations. Factor analysis of component N85 of VEP to stimuli with varying orientation and constant intensity revealed two-dimensional sensorial space of orientations. Also, the two-dimensional achromatic sensorial space was revealed for stimuli different only in intensities. In experiments with complex stimuli, two versions of stimulation were used. In the first version, four stimuli with varying orientation from 0 to 38.58 degrees were of 5 cd/m2 in intensity, the remaining four stimuli (from 51.44 to 90 degrees) were of 15 cd/m2 in intensity. In the sensorial space, stimuli with different intensities were disposed on the plane formed by the first two significant factors in the opposite quadrants, whereas within each quadrant, stimuli were arranged according to their orientation from minimum to maximum degrees. It is suggested that, in this version of stimulation, the interaction between two characteristics (intensity and orientation) took place with clear-cut dominance of the factor of intensity. In the second version of the experiments, also eight complex stimuli were used. Each stimulus was characterized by specific combination of orientation (one of the eight directions in the range from 0 to 90 degrees) and intensity (one of the eight intensities in the range from 5 to 21 cd/m2). Three or four significant factors were revealed in each test. Only the plane of intensity of sensorial space (XIX2) formed by two significant factors was revealed in the overwhelming majority of cases. On this plane, stimuli were arranged according to their intensities. This fact can be explained by specific (twilight) type of rabbit's vision with predominant discrimination of intensities. However, some findings suggest that visual evoked potentials reflect simultaneous processing of two characteristics of visual stimuli (intensity and orientation) being indicative of a possibility of the complex stimuli analysis in the primary visual cortex.

The responses of 83 neurons in the rabbit superior colliculus to substitution of color stimuli of different brightnesses and black-and-white stimuli of different intensities were studied. Superior colliculus neurons were found to respond with initial and late phasic discharges (over the periods 50–90 msec and 120–300 msec from the moment of stimulus substitution respectively), along with prolonged tonic discharges whose spike frequencies depended on the intensity of the stimulus. Analysis of the phasic responses of the neurons allowed three groups of cells to be identified. One group of cells (25 of the cells studied, 30%), identified on the basis of early neuron responses, were specialized for detecting brightness differences between black-and-white and color stimuli of different intensities. The sensory spaces reconstructed on the basis of spike discharge frequencies in the early discharges of these neurons were achromatic and two-dimensional. Another group of neurons (16 of the cells studied, 19%) were mainly identified on analysis of late phasic discharges and had four-dimensional spaces with two color and two achromatic axes. The third group of cells (four neurons, 5%) had early discharges with two-dimensional achromatic sensory spaces and late discharges with four-dimensional spaces. It is suggested that reconstruction of the four-dimensional space requires processing of information from the visual cortex on color and intensity differences between stimuli. The sensory spaces of superior colliculus neurons reconstructed on the basis of phasic discharges essentially coincided with the sensory spaces of neurons in the visual cortex and lateral geniculate body and spaces obtained by analysis of the N85 component of visual evoked potentials in rabbits recorded using similar stimulation. This may support the vector coding principle in the visual analyzer.

Changes in activity of 51 neurons in the rabbit lateral geniculate nucleus evoked by the replacement of eight color and eight achromatic stimuli in pairs were analyzed. It was found that neurons displayed the earliest phasic (within 50-90 ms after the replacement) and tonic response components. The earliest component strongly correlated with differences between stimuli, whereas the tonic component depended on stimuli intensity. Analysis of phasic component revealed two neuronal populations: the first group of cells was specialized for stimuli differentiation only by their intensities, and, and the second group could measure differences in colors and intensities. Neuronal perceptual spaces were reconstructed using the average of the earliest response component as a measure of differences between stimuli. Spaces of 44 neurons (86%) were two-dimensional with brightness and darkness axes. Such neurons had the same structures of space for color and achromatic stimuli. Spaces of 7 neurons (14%) were four-dimensional with two chromatic and two achromatic axes. The structures of perceptual space reconstructed from neurons in the lateral geniculate nucleus were identical to the spaces calculated from the neurons in the primary visual cortex. The structure of the perceptual space reconstructed from neuronal spikes was also similar to space calculated from the N85 visual evoked potential component recorded under similar conditions and to another space reconstructed on the basis of rabbit's instrumental learning. This fact confirmed the general principle of vector coding in the visual system. The tonic component of the most of neurons in the lateral geniculate nucleus showed a linear correlation with changes in intensities, thereby these neurons could be characterized as pre-detectors for cortical selective detectors.