Том 75, № 5 (2025)

The present paper describes backward conditioned connections (BCC) as a universal principle of brain activity. The first section analyzes the historical view of the problem: the discovery of the phenomenon of BCC, the rules and regularities of its manifestation (the role of the ratio of the strength of the paired stimuli, the duration of the conditioned stimulus, the time following after the unconditioned stimulus before the start of the conditioned stimulus, the number of pairings, and other factors). In the second section, some hypotheses explaining the formation, functioning, and role of bilateral conditioned connections in the process of organizing holistic behavior are considered. And the last section describes the current state of the problem of reverse US-CS connections – the study of 2nd-order conditioned reflexes, sensory preconditioning, stimulus equivalence analysis, and the role of context. The importance of dopamine in BCC and the role of these connections in memory reconsolidation are considered. Attention is paid to modern neurochemical, electrophysiological, optogenetic and other studies of the BCC.

Over the past decade, the main focus in functional magnetic resonance imaging (fMRI) studies on the structural and functional organization of the human brain has shifted from functional segregation, i. e., the functional specialization of individual brain structures, to functional integration, i. e., the collective activity of the brain systems. Currently, the most common type of fMRI study is the resting-state functional connectivity studies, due to the relative ease of obtaining and statistically analyzing data. At the same time, growing attention is paid to dynamic changes of functional connections during task performance. In this review, we briefly describe the nature of functional connectivity measured using fMRI, review existing task-modulated functional connectivity methods, and provide practical recommendations for choosing a statistical analysis method and planning the fMRI task design. In conclusion, we will discuss the significance and prospects of studying task-modulated functional connectivity for fundamental research into the systemic organization of the human brain in health and pathology.

In psychophysical experiments the mechanisms of interpolation and grouping in vertical and diagonal (45°) orientation of stimuli were studied. The orientation estimates of interpolated (mentally drawn through the points) and real lines were compared. The images were also presented in the presence of distractors – strokes with the same slope, which form the Zöllner illusion when they superimposed on straight lines. The distance between the points and the length of the lines were varied in the reference stimuli. It was shown that with a vertical orientation, the slope estimation thresholds for interpolated and real lines did not differ for all stimuli used, whereas with a diagonal orientation, the thresholds were higher. In the latter case, there is also a significant difference in the orientation estimates (illusions) of real and interpolated lines. The obtained data may evidence differences in the mechanisms of line slope estimation and interpolation in vertical and diagonal orientations, as well as a different number of neurons with receptive fields of such orientations.

This study is devoted to the investigation of neural correlates of attentional template formation in categorical search. The categorization process plays a crucial role in optimizing information processing and storage in working memory. Categories are divided into subordinate, basic and superordinate levels, which determine the degree of specificity and clarity of representation. Attentional templates contain attributes that define the target, such as color, shape, or size, and are activated in preparation for retrieval. The aim of the study was to examine the difference in the neurophysiological mechanisms of attentional template formation under the influence of verbally given categories of basic and superordinate levels. The category level (basic or superordinate) was manipulated, possible changes in N2pc (N2-posterior-contralateral component) and CDA (contralateral delay activity) amplitudes were recorded as well as behavioral measures. Behavioral results were consistent with other studies of visual search and categorization. The CDA component related to visual working memory load showed no statistically significant differences, whereas the N2pc component showed classic results for visual search paradigm – it changed with lateralization and with the number of stimuli, but no effect of category level was revealed. This study showed that there are differences at the behavioral level in a categorical visual search task, but they are absent for the CDA and N2pc components amplitudes – the effect may be manifested in oscillations; a block design is probably not suitable for assessing changes in CDA amplitude, verbal presentation of categories does not lead to differences in amplitude.

Epidemiological studies have identified a functional bidirectional relationship between chronic sleep loss and the development of obesity. However, it remains unclear whether these factors amplify the damaging effects of each other on neurophysiological functions. This study aimed to investigate the combined effects of high-fat diet (HFD) and chronic sleep restriction (SR) on sleep characteristics and destructive changes in the locus coeruleus in male Wistar rats. Consumption of HFD for 10 weeks did not lead to changes in the organization of the wake-sleep cycle compared to control animals receiving standard dry chow (SD). However, during SR in a polyphasic regimen of 3 h of wakefulness and 1 h of sleep opportunity using a rocking platform for 5 days, the compensatory increase in slow-wave activity in response to lost sleep was less pronounced in rats on HFD during one-hour rest periods than in rats on SD. During the recovery period, a decrease in the amount of deep slow-wave sleep (SWS) in both groups was detected. However, after 14 days, this parameter reached the baseline level in the rats on SD, whereas this did not occur in the rats on HFD. It was found that SR was accompanied by neuronal death in the locus coeruleus, and the combination of HFD and SR augmented neurodegeneration. Thus, we demonstrated for the first time that chronic SR and HFD leads to pronounced disturbances in the homeostatic mechanisms of SWS regulation and subsequent deterioration of sleep quality, which could be a consequence of progressive dysfunction of the noradrenergic system of the locus coeruleus. The identification of the mutual negative influence of HFD and SR on sleep neurophysiology can be considered as a new risk factor for the development of metabolic diseases and other disorders of CNS functions.

Histological and electron microscopic studies of dentate fascia neurotransplants in the somatosensory region of the rat neocortex were performed. It was shown that mature nerve tissue developed in the transplants with reproduction of the organotypic characteristics of differentiated neurons and glial cells. Particular attention was paid to the study of the cellular organization of the boundary between the transplanted and neocortical tissues (interface) as well as the possibility of neuronal processes growing through it. The leading role in the integrative process belonged to different subpopulations of astrocytes. Mature protoplasmic and fibrous astrocytes, as well as astrocytic precursors, and ependymal cells were identified at different sites of the interface. The cellular composition of the border influenced the degree of integration of the transplants with the adjacent brain, ranging from maximum integration in the astrocytic type of border to limited exchange of axonal and dendritic processes in the ependymal type. Fibrous astrocyte processes accompanied and guided bundles of axons and dendrites through interface. The only barrier to the growing nerve processes were the interface regions, into which large blood vessels penetrated from the pia mater.

Mice of two strains, differing by the relative brain weight (LB and SB) displayed differential behavioral effects after 7-day exposure to 50 mg/kg of memantine injections, the non-competitive NMDA-rec antagonist. Memantine increased the exploration behavior in LB mice as well as their reaction to novelty, while SB mice demonstrated the activation of behavior after the control saline injections. The number of newly developed neuronal elements in the hippocampal subgranular zone of dentate gyrus in LB (but not SB) mice subjected to memantine was higher in comparison to controls. In the intact samples of mouse strains used in this work no significant behavioral differences were found, which accentuated the genotype-dependent effects of memantine injections.