Interregional cortical interactions at different stages of natural sleep and the hypnotic state: EEG evidence

Abstract

Recent data on the neurophysiology and neurochemistry of sleep have led to a revision of views regarding the role of brainstem centers and basal ganglia involved in the modulation of wakefulness levels and the regulation of slow-wave and paradoxical sleep [1][2][3][4]. New data were obtained on the changes in the neurochemical activities of several precisely located deep structures of the brain, each of which is involved in the regulation of both wakefulness levels and sleep depth through periodic activation of inhibitory neurons of these structures [4]. These data confirmed that slowwave sleep plays a role in homeostasis and attracted more attention to the search for consistent patterns in the interrelations between individual cortical and brainstem regions as dependent on the depth of sleep.While considerable progress has been made in studying the neurophysiological mechanisms of natural sleep, intense studies of the hypnotic state at the new methodological level are in their infancy. It remains unknown why natural sleep and the hypnotic state are similar in some characteristics (e.g., behavioral parameters and the possibility of transition of hypnosis into sleep [5][6][7]) and are radically different in others, especially EEG parameters [8,9].The results of recent studies using positron emission tomography showed important topical characteristics of the selective activation and inactivation of cortical fields and some subcortical centers in hypnosis [10][11][12]. However, the undeniable advantages of computer tomography are still insufficient for obtaining necessary information on the changes occurring in the systemic interaction between different cerebral structures as the consciousness is narrowing.The interregional interactions of cortical biopotentials recorded in different periods of sleep also remain somewhat unclear [13][14][15]. Thus, which cortical regions change their functional relationships at different depths of natural sleep and the hypnotic state, as well as the extent of these changes, is still an open question. At the same time, detailed analysis of the patterns of cortico-subcortical integration under these conditions, taking into account the specificity of local changes in bioelectric potentials apparently determined by the modulating effect of subcortical centers, may be an effective approach not only to understanding the physiological mechanisms of the cerebral control of basic states but also to studying some important mechanisms of cognitive activity and the algorithm of retrieving trace memories.We searched for permanent characteristics of the spatial structure of the cerebral biopotential field at different stages of natural sleep and hypnosis in order to determine consistent neurophysiological patterns of the Abstract -The characteristic patterns of EEG spatial organization at different stages of natural sleep and the hypnotic state were studied in 26 volunteers aged 18-22 years. EEGs were recorded using 12 monopolar leads, and EEG cross-correlation coefficient matrices were calculate...

Characteristics of integrative brain activity during various stages of sleep and in transitional states

“…1a, 1b). This evidence confirms our previous reports [6,16], where we noted the potentially important role of the posterior temporal cortical areas, especially those of the right hemisphere in the organization of systemic brain activity during transition from the state of wake fulness to drowsiness and to the slow wave sleep stages.…”

“…The data of [16] are in agree ment with the results of this study; in adult subjects, weakening of interhemispheric EEG relationships in the anterior and posterior frontal areas also occurred at all successive sleep stages except for I (A).…”

“…In our previous report on the central mechanisms of deepening sleep and the hypnotic states [16], we suggested that a pronounced weakening of the interre gional interactions of the frontal cortical regions might reflect a particular pattern of the frontal area's activity during falling asleep; i.e., the inactivation process develops in these areas. The data of [16] are in agree ment with the results of this study; in adult subjects, weakening of interhemispheric EEG relationships in the anterior and posterior frontal areas also occurred at all successive sleep stages except for I (A).…”

“…We used factor analysis of the multichannel EEG, which made it possible to evaluate the involvement of the main systems of the brain's integration in the systemic interaction of various cor tical areas and subcortical structures [6]. We earlier found out [6,16] that, both in wakefulness and during sleep, the spatial structure of distant relations of brain potentials, which is assessed among common factors (I, II, III in the case of vector representation of multi channel EEG), reflects the brain's ability to maintain a stable topologically ordered system of distant inter regional relations that plays the role of background for the fast functionally specific processes and reactions. Systemic factors common for all EEG derivations reveal the effect of the main integrative brain systems on the arrangement of intercortical and cortico sub cortical relationships.…”

“…Earlier, we demonstrated [6,16,22] that factor I reflects a balance of the diffuse activating and synchro nizing effects of the brainstem regions on the cortex; these effects are mediated via the nonspecific thalamic nuclei. Factor II testifies to the degree of involvement of the long associative pathways of the neocortex (and of thalamo frontal and thalamo parietal integrative systems) in the coordination of the bioelectrical activ ity of the cortical fields in the fronto occipital direc tion of each hemisphere.…”