Behavioral experiments were run to assess the ability of rhesus monkeys to retain visual objects differing in shape, color, or a combination of these features in working memory. Six male rhesus monkeys performed a delayed matching-to-sample task in which three geometric shapes from a set of stimuli served as samples. In the first series of experiments, these were different colored figures of different shapes; samples in the second series were circles of different colors and samples in the third series were monochrome images of a number of figures from the stimulus set. Use of both cues to retain objects in memory resulted in the best performance by the monkeys; animals generally performed better on the color-matching task than the shape-matching task. This result is inconsistent with data reported from a number of other studies, where similar experiments – but with only one sample for memorization – yielded the opposite trend. The reason for this difference may be a shift in the focus of attention from local features (figure outlines) to global features (color) for memorization of information in the conditions of greater load on working memory used in our study.

In neurophysiological studies, functional magnetic resonanceimaging (fMRI) is most commonly used to map brain functions by locatingareas of increased activity while executing various tests. At thesame time, less attention is traditionally paid to a concomitantdecrease in metabolism in other brain areas despite a comparableintensity of these processes. The cause for such a decrease in localbrain activity, as well as its dynamics and the dependence of localizationon experimental conditions, are currently in question. The aim ofthis work was to study the interaction between brain regions thatdemonstrate bidirectional changes in the level of oxygen consumptionin response to the simplest stimuli, flashes of light. The studywas carried out on three awake Macacamulatta monkeys, in which activity distribution mapswere compared during aperiodic light stimulation and in total darkness.Flashes of light evoked an increase in oxygen consumption in theprimary visual cortex and a simultaneous decrease in this indicatorin field 7 of the parietal cortex and in area V5 of the middle temporalarea. Brain areas that decreased their activity usually did notrespond to flickering light stimulation and were not involved insignal processing under conditions of our experiments. The dataobtained are interpreted in the light of the hypothesis of an automaticmaintenance of a balance between activated and deactivated brain areas,aimed at saving brain energy resources. Presumably, a decrease inactivity relative to the background level in unused areas wouldhelp compensate for increased energy consumption in other brainareas responsible for signal processing.

It is well known that rhythmic light stimulation can alter the electrical activity of the human and animal brain. Moreover, the brain response to certain flicker frequencies significantly exceeds the responses to neighboring frequencies. This phenomenon is thought to be related with the effect of resonance, as evidenced by the coincidence of one of the maxima in the profile of the response to flashes with the frequency of the alpha rhythm. However, other frequencies that cause an increased response to flashes are not reflected in electroencephalogram (EEG) as dominant oscillations. The goal of this study was to reveal the relationship between local maxima in the profile of the responses to flashes of different frequencies and dominant brain oscillations recorded in electrocorticogram (ECoG) of rhesus monkeys without stimulation. The study was carried out on four male Macaca mulatta individuals. In three animals, peak responses were elicited by flickers at 8 and 16 Hz, while one monkey showed a second peak in the 22−30 Hz range. The first maximum (8−10 Hz) in the profile of the response to rhythmic photostimulation coincided with the dominant rhythm recorded in the occipital and parietal regions at rest. The second maximum at 16 Hz coincided with the dominant ECoG rhythm in one of the primates when it was in the state of emotional arousal, which may account for the resonant origin of the increase in responses in this frequency range. The data obtained indicate that dominant brain rhythms, including latent rhythms revealed only by rhythmic photostimulation, can coincide in frequency in monkeys and humans. Neuronal mechanisms of selective sensitivity of neural networks to different frequencies of photostimulation are discussed.

Rhythmic light stimulation can alter the electrical activity of the human and animal brain. Moreover, the brain response to certain flicker frequencies significantly exceeds the responses to neighboring frequencies. This phenomenon is thought to be related with the effect of resonance, as evidenced by the coincidence of one of the maxima in the profile of the response to flashes with the frequency of the alpha rhythm. However, other frequencies that cause an increased response to flashes are not reflected in electroencephalogram (EEG) as dominant oscillations. The goal of this study was to reveal the relationship between local maxima in the profile of the responses to flashes of different frequencies and dominant brain oscillations recorded in electrocorticogram (ECoG) of rhesus monkeys without stimulation. The study was carried out on four male rhesus monkeys Macaca mulatta . In three animals, peak responses were elicited by flickers at 8 and 16 Hz, while one monkey showed the second peak in the 22–30 Hz range. The first maximum (8–10 Hz) in the profile of the response to rhythmic photostimulation coincided with the dominant rhythm recorded in the occipital and parietal regions at rest. The second maximum at 16 Hz coincided with the dominant ECoG rhythm in one of the primates when it was in the state of emotional arousal, which may account for the resonant origin of the increase in responses in this frequency range. The data obtained indicate that dominant brain rhythms, including latent rhythms revealed only by rhythmic photostimulation, can coincide in frequency in monkeys and humans. The mechanisms behind the selective sensitivity of neural networks to different frequencies of photostimulation are discussed.

Behavioral experiments were run to study the capacities of Macaca mulatta monkeys to perform cognitive tests of different levels of difficulty presented on a computer touch screen. The task consisted of recognizing the dominant orientation in textures with different levels of ordering. Rates of learning were analyzed, along with the proportions of correct responses and task solution times in relation to task difficulty. The extent of exploratory activity was evaluated in parallel, in terms of reactions to unfamiliar objects (the “reaction to a novel object” test). The proportion of correct responses increased with increases in the ordering of the test images and was comparable with results obtained previously in humans in similar experimental conditions. In monkeys, the index of exploratory activity correlated with the rate of learning and was lower in those animals inclined to distraction of attention, i.e., with longer response times. The results obtained in monkeys allow the neural processes occurring in the human brain on recognition of objects to be modeled, from the encoding of the physical properties of images to decision-taking. The interaction between the level of exploratory activity and the rate of learning allows the “reaction to a novel object” test to be used for selecting potential individuals for participation in behavioral experiments, significantly reducing the time spent on training the monkeys to new tasks.

In behavioral experiments rhesus macaque monkeys were trained to interact with the computer using a tactile display. We used grayscale Gabor patches of low spatial frequency as stimuli. Monkeys' task was to touch the screen with his hand in the area of the target stimulus, followed by automatic food or juice reinforcement. After two successive correct answers, stimulus contrast gradually decreased. Using a two-alternative forced choice method the contrast threshold was measured within which monkeys can detect the appearance of low-frequency images. It was shown that the contrast sensitivity decreased with the decrease of stimulus spatial frequency, while the reaction time increased. The findings extend our knowledge of the primates' activity in the virtual environment and open new possibilities for modeling and studying various human diseases.

Neuronal mechanisms of description of local properties of visual object light-shadow surfaces are studied. Earlier we have shown the cat lateral geniculate body (LGB) neurons to have sensitivity to the value and direction of brightness vector in loci of object light-shadow surfaces. Further study of properties of orientation selectivity (OS) of these neurons has revealed that single LGB cells sensitive to direction of brightness gradient vector also have the classical OS to direction of the test bands. Such complex orientation sensitivity of neurons to direction of binary and light-shadow fragments of visual objects is of essential significance, in our opinion, for understanding of principles and mechanisms of the object vision.