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Biomedical subjects

I V Chueva

Publications and source records attributed to I V Chueva.

At least 73 records · Page 4Linked to original sources
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Relationship between the characteristics of visual short-term memory in monkeys and the spatial properties of images.

Experiments were performed on Rhesus macaques to study the relationship between delayed visual differentiation processes and stimulus properties. These investigations showed that the processes of short-term storage of visual information in monkeys has significant features associated with differences in stimulus properties. These consisted of different durations of storage and motor response times. Because of these differences, stimuli (15 pairs) could be grouped into compact clusters on the bases of similarity between their delayed differentiation characteristics. These experiments characterized the processes of short-term information storage during the differentiation of stimuli differing in terms of spatial relationships between elements, as compared with stimuli differing in terms of other attributes (shape, color, etc.); spatial information was stored for shorter periods of time and motor response times were longer. It is suggested that visual short-term memory involves a set of mechanisms operating on attributes of different types and which, along with signs and working programs associated with the visual system, stores spatial discriminatory signs, in which the major role is played by visual-vestibular interactions.

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Relationship between learning characteristics and the properties of visual objects in Rhesus macaques.

Behavioral studies were carried out on Rhesus macaques to investigate the relationship between the processes of learning a visual differentiation task and various properties of the stimuli, with the aim of identifying the effect on learning of a cognitive factor such as the biological significance of the visual object. Cluster analysis of a number of features of the learning process was used to distinguish visual stimuli (16 pairs) into separate compact classes of similar objects, each of which appeared to be characterized by its level of biological significance. A scheme describing the learning process, and including an assessment of the significance of sensory information, is proposed.

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Relationship between learning characteristics and the properties of visual objects in rhesus macaques with bilateral removal of parietal cortex field 7.

Behavioral experiments were used in rhesus macaques with bilateral excision of field 7 of the lower parietal cortex to study the relationship between visual differentiation learning processes and a variety of stimulus properties. All animals showed significant differences associated with stimulus properties, which produced different types of learning curves. For each monkey, visual stimuli were divided into compact groups in terms of the "similarity" of their learning characteristics. Removal of field 7 had no effect on the process of learning visual image discrimination when this was based on properties such as color and geometrical shape, but worsened the learning characteristics when visual differentiation was based on spatial information, when the learning process became unstable, with increases in the numbers of peaks and troughs on the learning curve and a significant increase in the duration of the learning period. The time to a stable motor response also became significantly greater than for visual images distinguished by shape and color. It is suggested that during the process of learning visual discrimination, processing and extraction of image signs by the visual system for objects characterized by spatial relationships is accompanied by the formation of spatial distinguishing signs, this process involving neuronal structures in field 7 of the lower parietal cortex, which appears to be the main area determining visual-vestibular interactions. Increases in oscillations and in the difficulty of the learning process for differentiation on the basis of spatial information after removal of field 7 might be due to a transfer from one strategy to another, resulting from disruption of the mechanisms which evaluate body image and egocentric orientation on the basis of visual-vestibular interactions.

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The effects of an NDMA receptor antagonist on delayed visual differentiation in monkeys and rearrangements of neuron spike activity in the visual and prefrontal areas of the cortex.

The effects of perfusion of field 17 with the glutamate receptor antagonist 2-amino-5-phosphonovaleric acid (APV) on the characteristics of visual recognition and short-term memory were studied, along with the effects of APV on the responses of neurons in the visual and prefrontal areas of the cortex in rhesus macaques. In the test for delayed visual differentiation of stimuli of different colors, behavioral data were recorded simultaneously with multichannel recordings of the spike activity of single cells in cortical field 17 (directly within the microdialysis zone) and field 8. Multifactor dispersion analysis (ANOVA) showed that APV significantly worsened the behavioral characteristics in monkeys, with significant reductions in the duration of short-term storage of information (by factors of 2-4) and significant increases in the motor response times. These changes in cognitive characteristics induced by APV were accompanied by changes in the spike activity of neurons in the visual and prefrontal areas of the cortex during the sensory analysis and delay stages; changes in spike activity consisted of significant desynchronization. These results show that cognitive dysfunctions consisting of worsening of short-term remembering of information and increases in the duration of motor responses during exposure to APV may be caused by desynchronization of neuron activity in various areas of the cortex, these being involved in neuron ensembles responsible for the mechanisms of short-term memory, in which glutamatergic structures play an important role.

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Neurophysiological correlates of delayed visual differentiation tasks in monkeys: the effects of the site of intracortical blockade of NMDA receptors.

A delayed visual differentiation task using stimuli of different colors was used in rhesus macaques to study the characteristics of visual recognition, short-term memory, and the responses of neurons recorded simultaneously in the visual and prefrontal areas of the cortex, along with their relationships with the site of intracortical (fields 17 or 46) perfusion of the glutamate receptor antagonist 2-amino-5-phosphonovaleric acid (APV). The behavioral characteristics and spike activity of individual cells in cortical fields 17 and 46 were recorded before and after perfusion with APV and after washing away of traces of APV. Multifactor dispersion analysis showed that the effect of APV in monkeys consisted of decreases in the probability of correct responses, leading to a decrease (two-fold) in the duration of short-term storage of information and a significant increase in the motor reaction time. The probability of correct solutions depended on the site of APV perfusion in the cortex, while the motor response time was independent of the perfusion site. Perfusion of field 46 with APV, unlike perfusion of field 17, altered the spike activity only of neurons in the prefrontal cortex, while no significant changes were seen in the neuron activity of the visual cortex. The actions of APV were accompanied by significant desynchronization of neuron activity in these two areas as compared with the level of synchronization in normal conditions; after traces of APV were washed away, the extent of desynchronization decreased. The neurophysiological correlates of cognitive dysfunctions associated with degradation of visual recognition and short-term memory due to modification of glutamatergic structures by blockade of NMDA receptors are discussed.

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[The effect of cholinergic substances on the mechanisms of visual recognition in monkeys].

In monkeys (Macaca mulatta) instrumental reflex was elaborated with differentiation of black-and-white and colour visual stimuli in condition of systemic administration of pharmacological preparations selectively influencing the functional state of cholinergic brain structures. Differentiation of black-and-white and colour stimuli is not disturbed by atropine (0.1 mg/kg) and amizile (up to 1.5 mg/kg) injections; at greater doses frustration of the instrumental reflex takes place. Differentiation of black-and-white and colour stimuli is disturbed at injection of various doses of antidepressant phthoracizine: 5 mg/kg and 7 mg/kg, respectively. These disturbances are restored by the injection of definite doses of galantamine; for correction of colour differentiation a greater dose is required. The obtained data point to differences in neurophysiological and neurochemical processes responsible for black-and-white and colour vision.

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[Differences in the perception of periodic and non-periodic visual stimuli in rhesus macaques].

Differences in perception of periodic and non-periodic visual stimuli were studied in rhesus monkeys during elaboration of an instrumental reflex. In the process of learning selectivity was formed (within the frequency band of 0.5 = 1 octave) for each spatial frequency used as positive stimulus. The selectivity to a definite bar width was less expressed, and a more prolonged learning was needed for its formation. There was no complete transfer from the positive grid frequencies to stimuli consisting of one or two bars with a width equal to a half-period of these frequencies. The distributions of choices acquired in the process of differentiation of vertical stimuli were preserved when their orientation was changed to the horizontal one for bars of definite width. This fact points to a complete transfer of this selectivity, while its considerable widening for spatial frequencies testifies to the absence of complete transfer of frequency selectivity.

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[Learning characteristics and long-term memory in rhesus macaques].

The use of entropy of choices distribution in studying the processes of learning and long-term memory in rhesus monkeys during differentiation of periodic and non-periodic visual stimuli, showed that the transition from the unlearned state to the learned one proceeds not gradually but in two stages; the first stage--the accumulation of information and externally random behaviour, the second stage--rapid transition to the learned behaviour. For "filters" selective to spatial frequency, the change of stimuli orientation leads to an increase of the behaviour entropy. For "filters" selective to the bar width, the entropy practically does not change. During prolonged storage of acquired information, in the long-term memory, its partial loss takes place leading to an increase of the behaviour entropy. The difference between the entropy determined directly after the learning and that determined again after a prolonged storage of the memorized habit characterizes the quantity of information lost during the storage period.

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[Types of spatial frequency filters in the cat visual cortex].

Three types of receptive fields (RF) were revealed in the studies of mechanisms of spatial-frequency filtration in the cat's visual cortex. The spatial-frequency selectivity of RF of the first type (mainly simple fields) manifests itself in a narrow range of the gratings orientations close to the preferable one, being absent beyond this range. Two other types of RF (mainly complex and hypercomplex ones) are selective to the spatial frequencies at any gratings orientation. At such gratings orientation RF of one type respond with frequency-selective inhibition, RF of another--with frequency-selective excitation. For the majority of RF the two-dimensional spatial-frequency selectivity is realized at short lengths of gratings at which the orientation selectivity of RF is not manifested. A conclusion is drawn that the twodimensional spatial-frequency filters are not Fourier filters.

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[Structural differences of spatial-frequency filters in the cat visual cortex].

Sensitivity profiles of receptive fields (RF) of the cat's visual cortex along the width and length of the field were determined. They served as criteria for determining structural differences of the earlier discovered types of spatial-frequency filters. It has been shown that RF with spatial-frequency selectivity in a narrow range of orientations close to the preferable one, have the "one-dimensional" sensitivity profiles in the same range. For RF showing spatial-frequency selectivity along the RF length and width two-dimensional sensitivity profiles along these RF dimensions were revealed. A group of fields was found whose pattern of sensitivity profiles depended on the geometrical properties of images which stipulated the functional changes o RF filtering properties. Possible role of different types of spatial-frequency filters in image processing is discussed.

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