V. T. Shuvaev

The Role of the Basal Ganglia in Organizing Behavior

gested by Pavlov, that the acquired conditioned reflex is a complex physiological and psychological manifestation, including mechanisms of sensory analysis, directed attention, activation of past experience, motivation, formation of a dominant state in brain centers, prediction of a future action, evaluation of the state of the external and internal environments, consistent changes in the autonomic and endocrine reactions, and many other factors not associated with detectible external measures of reflexes. During the first period of study of higher nervous activity, Pavlov, followed by all prominent physiologists throughout the world, focused attention on the roles of the cortical parts of the brain in forming conditioned reflexes. These studied led to the identification of many of the fundamental mechanisms underlying higher nervous activity. However, Pavlov and his students recognized that the normal functioning of the mechanisms forming new types of behavior required a continual relationship between the operation of the cortex and subcortical brain formations. Studies of the systems organization of behavior, the roles of cortical and subcortical brain structures in the mechanisms of higher nervous activity, assessment of the specific contributions of these formations to the processes of learning, memory, and thinking, and identification of the characteristics of complex interactions of cortical-subcortical systems were so difficult that much has remained unresolved to the current time and requires new additional investigations with the different approaches provided by psychologists, mathematicians, engineers, programmers, geneticists, doctors, morphologists, etc. One of the most important and interesting approaches is that investigating the roles and mechanisms of interaction of various cortical and subcortical neural formations. Most investigators addressing this question to some extent or another come to the conclusion that the special complexity in understanding these processes results from the basal ganglia (caudate nucleus, putamen, globus pallidus, claustrum, amygdaloid body). Many investigators include the substantia nigra and subthalamic nucleus as part of the basal ganglia. Some 340 years have passed since the English anatomist Thomas Willis first described the basal ganglia in mammals [30]. However, it was only in 1965 that the first Russian studies, in our laboratory, aimed at investigating the physiology and morphology of individual nuclei of the basal ganglia and their roles in organizing behavior, were started. Many investigators have established that the basal ganglia are involved in the mechanisms underlying performance of the most important body functions, such as voluntary movement, attention, learning, memory, and many others [1, 2, 4, 6, 8, 9, 12, 17, 20, 22]. Our concepts of the structure and functional organization of the basal ganglia have changed significantly over the last 10–15 years. This is to a significant extent due to the use of complex approaches to studying these subcortical structures, with a wide range of methodological approaches: behavioral, psychological, electrophysiological, neurochemical, electron-microscopic, immunohistochemical, positron emission tomography, nerve tissue transplantation, etc. Results obtained from experimental and clinical studies performed using these methods have provided the basis for a series of principles underlying the activity of cortical-subcortical systems, in which the basal ganglia play an important part. Starting with the clinical studies of Laursen [26], which prophetically predicted that the functions of the striate nuclei might not be limited to their involvement in Neuroscience and Behavioral Physiology, Vol. 34, No. 3, 2004

Genetic Determination of Neurophysiological Mechanisms of Cortical-Subcortical Integration of Bioelectrical Brain Activity

The contribution of genetic factors to the formation of the neurophysiological mechanisms of cortical-subcortical integration was studied in 12 pairs of monozygotic and five pairs of dizygotic twins (aged 18–25 years). Intrapair similarity of the nature of spatial interactions between bioelectrical activity in the cerebral cortex, assessed from different combinations of statistical interactions of EEG from 16 monopolar recordings, was assessed in each pair of twins (and among 544 non-related pairs of subjects in both groups). The results suggest a high level of general population invariance and relatively small inherited and phenotypic variability in the morphofunctional systems making up the major neurophysiological mechanisms of brain integration as a whole. The ontogenetic formation of stem and subcortical regulatory structures, which have a leading role in the systems combination of different parts of the brain into a single formation, appears to occur in all individuals by the same principle, as disturbance can apparently affect the fundamental monomorphic features of the species. In turn, we might expect to find large interindividual variability in the establishment of interregional connections of the neocortex, the role of inherited and environmental factors being different in the processes forming long and relatively short intercortical interactions.

Effects of selective visual attention in the parietal and temporal areas of the human cortex using evoked potential data

Studies of 11 young subjects addressed the analysis of evoked potentials in the parietal and temporal areas to sequential presentation of visual symbols on the left and right sides; symbols were squares and circles and were observed passively and in conditions of selective attention to target stimuli presented to the subjects in random order and requiring rapid and precise motor responses. Comparison of monopolar evoked potentials in leads P3, P4, T3, T4, T5, and T6 with bipolar potentials in leads P3-T3, P3-T5, P4-T4, and P4-T6 in conditions of passive and selective attention showed that voluntary attention was accompanied by significant rearrangements in evoked activity in the parietal and temporal areas. This was evident as: 1) an increase in correlations between evoked potentials in the parietal and temporal areas; 2) stabilization of monopolar evoked potentials over time, i.e., increases in the correlations of sequential evoked potentials, in both associative visual areas; 3) stabilization of bipolar parietal-temporal evoked potentials in terms of increases in their sequential correlations. It is suggested that selective attention facilitates linked activity of the two associative areas, which is needed for performance of visual selection.

Characteristics of activation in the parietal areas of the cortex in humans in different types of visual attention.

The state of cortical activation in the parietal and temporal areas was assessed using evoked potentials (EP) during the tasks of selection of lateralized visual stimuli requiring three different types of attention: to stimulus shape, to stimulus position, and to both. Studies in 15 young, healthy subjects involved recording of EP in six cortical leads: P3, P4, T3, T4, T5, and T6, with analysis of the endogenous EP components CNV, N1, P3, and the EP complex [N1-P3] (according to standard terminology). Changes in EP components in response to the attended and non-attended stimulus features were compared. Differences between them were assessed using the index of selectivity of attention to one or another feature of the visual stimuli. In the parietal area, selectivity was seen in conditions of attention to stimulus position and attention to stimulus shape. In conditions of simultaneous attention, the indexes of selectivity were essentially equal to the sum of the indexes of selectivity of attention to shape and position. The most marked endogenous EP components (CNV, N1, and P3) in visual selection were seen in the parietal areas, with a greater gradient of increased activation of the parietal areas of the cortex as the need for attention increased, along with a lower threshold for the action of attention, and anticipatory development of the P3 wave in the parietal area as compared with the temporal area. These results suggest that the parietal cortex has priority in the visual attention system and that the magnocellular (M) pathway forms the most important visual input to the dorsal parietal area of the neocortex.

Interhemisphere differences during tasks involving attention and selection of lateralized stimuli

The state of cortical activation in the parietal and temporal areas of the right and left hemispheres was evaluated using evoked potentials (EP) during tasks consisting of selection of visual stimuli lateralized in the right and left visual fields and needing three different types of attention: to stimulus shape, to stimulus position, and simultaneously to stimulus shape and position. EP were recorded in 15 young healthy experimental subjects using six cortical leads: P3, P4, T3, T4, T5, and T6; the following endogenous EP components (in standard terminology) were analyzed: contingent negative variation (CNV), N1, P3, and the N1-P3 complex. Asymmetry in evoked potentials was assessed in terms of differences to contra-and ipsilateral stimuli in the right and left hemispheres. EP asymmetry was detected in the right hemisphere in all types of selection of lateralized stimuli. The magnitude of asymmetry in the right hemisphere depended on the level (or intensity) of attention: the degree of asymmetry increased with increases in the need for attention to analyze the stimuli. There was a significant relationship between the magnitude of asymmetry and the latent periods of the subjects’ responses. The functional significance of these data demonstrating asymmetry may be that it provides better spatial differentiation of visual signals in the right hemisphere, along with dominance of the right hemisphere in attention tasks.

Changes in Evoked Potentials on Increases in the Difficulty of Visual Searches in Humans

Monopolar evoked potentials (EP) in the frontal, parietal, temporal, and occipital leads in 16 young healthy subjects were analyzed during visual searches of increasing difficulty. Increases in the complexity of the visual search and addition of “noise” to visual stimuli added significant difficulty to the image recognition task, which was reflected in increases in search times and errors. Correlation of changes in EP and search parameters was seen mainly in the frontal leads: there were significant positive relationships between the N2 and P4 components and the SN–SP difference wave on the one hand and search difficulty on the other; there was a negative relationship with the P3 component, probably due to an increase in the duration and amplitude of the preceding N2 component. The N2 and P4 components were most marked in the frontal leads. We suggest that these data provide evidence of increasing dominance of frontal structures in the attention control system as the visual task increases in difficulty.

Cross-interval histograms for analysis of brain electrical activity.

A method for constructing cross-interval histograms for time-localized EEG fragments of particular types is described. The basic principles of the method are presented. Examples of cross-interval histograms constructed for EEG extrema and their derivatives are presented. Cross-interval histograms were shown to include peaks, troughs, and other features. Cross-interval histogram and cross-correlation histograms are compared. The method yields qualitatively new data on interactions between changes in biopotentials in different areas of the brain and allows rapid processes to be studied.

Activation of Extrastriate Cortical Areas in a Human during Selection of Visual Stimuli by Their Shape and Localization: Analysis of Evoked Potentials

Monopolar evoked potentials (EPs) in the parietal and temporal leads were recorded in 23 young, healthy subjects in the process of selection of visual stimuli by shape and localization. Two different central stimuli (selection by shape) and two similar right and left stimuli (selection by localization) were presented in the first series. Two simple right and left stimuli were presented in the second series, and a subject had to respond either to their shape or their localization. During spatial attention and shape recognition in both tasks, characteristics of the prestimulus negativity (contingent negative variation (CNV)) and negative–positive N1–P3 complex pointed to the predominant activation of the parietal areas. The greatest differences were observed in the late P3b component, associated with the “late” selection, rather than in the early EP components. The dominance of parietal activation as compared to temporal activation was associated with attention demands; i.e., the dominance was highest in the case of target stimuli and was least pronounced during passive perception of stimuli. It is suggested that the parietooccipital visual system leads in tasks demanding spatial and nonspatial attention to stimuli in a simple visual environment (without surrounding elements).

Spatial structure of EEG in depression patients with co-occurring anxiety disorders

This study was carried out on 36 patients with reactive depression and recurrent depressive episodes accompanied by severe anxiety disorder. Cross-correlation analysis of the spatial structure of the brain bioelectric activity has been performed. It have been found that clinical features of depression and anxiety disorder affect the spatial EEG structure depending on the type of anxiety disorder.

Features of the organization of the cerebral cortex bioelectric potentials and visceral state in neurotic depression

Studies were conducted with the participation of 20 patients with different classical variants of neurotic depression. The spatial organization of the bioelectrical activity of the brain was studied with the method of cross-correlation and coherent analysis. The autonomic-visceral state was assessed by the results of the auricular cryoreflex test (measurement of the cold sensibility of auricular points). The clinical picture of neurotic depression was shown to be reflected in the structure of the EEG spatial organization, which is modified depending on the degree of neurotic depression and the concomitant anxiety and asthenic syndromes. In the group with depressive syndrome without concomitant asthenic or anxiety manifestations, most changes were revealed in the right frontotemporal-left posterotemporal region. A cross-correlation and coherence decrease in the frontotemporal regions of both hemispheres and markedly increased cross-correlations in the right posterotemporal region were revealed in the depression + associated anxiety group. In the group where the depressive and anxiety syndromes were associated with marked asthenic manifestations, decreased cross-correlation and coherent relations in the frontotemporal regions of both hemispheres were observed. The clinical picture of neurotic disorders is reflected in a specific pattern of variations in the spatial organization of electrical activity of the cerebral cortex and in variations in the autonomic visceral state parameters. The development of negative emotional states in humans is accompanied by changes in the visceral functions. Variations in the central brain structures involve the zones of representation of emotional reactions and the zones of cortical representation of the organs. Insignificant central variations may cause autonomic dysfunction.