Analysis of the spatial-temporal EEG organization as the way to the knowledge of neurophysiological mechanisms of the integrative brain activity

Short results' review of investigations of Laboratory of Neurophysiology of Child of Sechenov Institute is presented in the article. Investigations are based on concept of academic M.N. Livanov about special role of spatial-temporal relations of brain potentials oscillations of various brain areas in providing of functional connection between them. It is shown, that in rest condition the structure of interregional relations of cortex biopotentials in all healthy people is characterized by high spatial orderliness that obviously assists to optimal realization of informational processes during various functional conditions from rest to complex cognitive functions. Special attention is given for the problem of functional signigicance of phase shifts of EEG waves. Data, that allows concluding that brainstem and thalamocartical integrative systems are characterized with relatively small inherited and phenotypic variability whereas fiber systems of both hemispheres that provide processes of intercortical integration are characterized by more expressed inter-individual variability, is presented. Intensive development of long associative and commissural tracks of telencephalon that joined even the most distanced cortical regions of hemispheres in united formation apparently results in formation of morpho-functional "skeleton" of neocortex, that occurred to be the basis for origin of qualitatively new (in comparison to animals) principals of formation of system organization of integral activity of the brain. Existence of long mono- and oligo-synaptic connections provides conditions for correlative develoment in ontogenesis of new function that is not conditioned by phylogenetic development.     

Selective attention in dogs from energy characteristics of neocortical potentials in the 1-220 Hz band

The state of selective attention was studied in dogs in the course of instrumental conditioning. During interstimuli intervals, this state was manifested in the state of strained waiting for conditioned stimuli. Electrical activity of different areas in both hemispheres was analyzed using the Fast Fourier Transformation. It was shown that in the process of development of selective attention, the high-frequency EEG components (40-200 Hz) in the motor area of the right hemisphere and the visual and parietal areas of the left hemisphere had a predominant significance over the traditional EEG frequencies of 1-30 Hz. The state of selective attention was characterized by another functional mosaic organization of the neocortical potentials.     

The mechanisms of the formation and the role of the oscillatory activity of the neuronal populations in brain systemic activities

Experimental findings and theoretical concepts that have led to a new insight into the neurophysiological mechanisms underlying information processing and brain state are presented in this review. It is assumed that the brain information processing associated with elementary neuronal assembles is reflected by oscillations in the range of 30-70 Hz and their spatio-temporal organization in millisecond intervals. He functional brain state associated with the non-specific systems is reflected in synchronization or desynchronization of activity of large neuronal populations in the frequency range of 20 Hz.     

Functional significance of high-frequency components of brain electrical activity in the processes of gestalt formation

A review. Current views of the so-called binding problem, which considers hypothetical mechanisms of perception of sensory stimuli and formation of their corresponding Gestalts (internal images) are discussed. The mechanism of intensification of synchronized reactions of cortical electrical activity in the gamma band frequency (30-80 Hz) is the basis of the most popular point of view of "binding". The article considers the evidence for the functional significance of the high-frequency components exceeding the gamma-range (to 200 Hz) obtained by the author, the origin of these oscillations, and conditions of their focal derivation. The problem of "binding" and stages of instrumental conditioning (a stimulus, perception of the stimulus, and its transformation into a signal) as well as significance of the context in learning and formation of tonic states ensuring the realization of phasic reactions is discussed. Forms of "binding" at the final stage of conditioning (selective attention) are considered. The question is posed as to whether "binding" is exhausted only by the mechanisms of synchronization of activities of large neuronal populations and only in the frequencies of the gamma range.     

Study of selective attention in dogs by coherent-phase characteristics of cortical potentials in the broad frequency band 1-220 Hz

Coherent-phase characteristics of cortical potentials (1-220 Hz) derived from different cortical point of both brain hemispheres of dogs were analyzed in the state of selective attention developed in the course of instrumental food conditioning. Among the compared cortical points, functional groups were found that were probably of priority for the state of selective attention. Values of coherence function between these derivations (an assessment of temporal relations) were at a certain optimal level (about 0.7), predominantly, in the frequency ranges of 1-15 and 40-200 Hz. Under such conditions, if the average phase shifts between the potentials were near zero, phenomenon of potential synchronism was formed. In case of significant phase shifts, phenomenon of asynchronous temporal relations with a certain spatial direction developed.     

The mosaic structure of the high-frequency range of neocortical electrical activity in dogs

The study was aimed to reveal the subbands of correlated changes in power spectral density of brain electrical activity (EA), including the low-voltage (up to 10 microV) high-frequency (HF) components (40-200 Hz) in dogs during instrumental conditioning by means of factor analysis. The values of the EA spectral density in interstimulus intervals calculated with a resolution of 1 Hz were used for subsequent factor analysis (the standard principle component technique with varimax rotation). Twenty factors could explain about 80% of total variance. The groups of frequencies which were presented by comparatively narrow peaks (2-3 points) of high loads (more than 0.6) of single factors ("stable" factors) were taken into consideration. In the process of conditioning the factor organization of the EA became substantially complicated, the number of the "stable" factors increased. It was originally shown that the high loads of these factors divided the HF band in comparatively narrow frequency subbands, which appear to reflect the functional mosaics in the neocortex.     

In search for neurophysiological criteria of altered consciousness

Neurophysiological approaches to brain mechanisms of consciousness are discussed. The concept of spatial synchronization of nervous processes developed by M.N. Livanov is applied to neurophysiological analysis of higher brain functions. However, the spatial synchronization of brain potentials is only a condition for information processing and does not represent it as such. This imposes restrictions on conclusions about the neural mechanisms of consciousness. It is more adequate to use the concept of spatial synchronization in views of consciousness as a psychophysiological level along with sub- and superconsciousness in three-level structure of mind according to P.V. Simonov. Forms of consciousness interaction with other levels concern the problem of altered consciousness and may be reflected in various patterns of spatial organization of brain potentials.     

The effect of scopolamine on the spatial organization of rat cortical potentials

The influence of scopolamine (1 mg/kg, i.p.) on the spatial organization of the neocortical electrical activity was studied in rats. A decrease in the spectral power and coherence of brain potentials in the range of the dominant theta-rhythm peak (6.00-7.25 Hz) and their increase in the adjacent low-frequency band were observed. Both indices were decreased in the wide beta band (19.00-30.00 Hz). The described changes took place over the whole areas of the right hemisphere and parieto-temporal region of the left hemisphere. The obtained results are discussed with respect to the role of the cholinergic brain system in the higher nervous activity.     

EEG spatial organization and activation of creative processes

Characteristic features of the spatino-temporal EEG organization of 24 right-handed children (aged from 8 to 13 years) were studied after stimulation of creative activity by the method of self-regulation of the brain functional state (Russian Inventor's Certificate no. 2157707, 01.06.1999). The multiparametric analysis of baseline recordings derived from 24 cortical points made it possible to find the most probable pattern of changes in the spatial synchronization of biopotentials, including increase in activity in the right anterior and left posterior cortical regions. These changes were accompanied by a rise in the information-energy parameter (the ratio between coherence and spectral power of potentials). This phenomenon may testify to a transition to the "economic" condition of information processing. Differences in EEG frequency characteristics corresponding to different levels of imagination and creative intuition were revealed.     

Different origins of gamma rhythm and high-gamma activity in macaque visual cortex

During cognitive tasks electrical activity in the brain shows changes in power in specific frequency ranges, such as the alpha (8-12 Hz) or gamma (30-80 Hz) bands, as well as in a broad range above ～80 Hz, called the high-gamma band. The role or significance of this broadband high-gamma activity is unclear. One hypothesis states that high-gamma oscillations serve just like gamma oscillations, operating at a higher frequency and consequently at a faster timescale. Another hypothesis states that high-gamma power is related to spiking activity. Because gamma power and spiking activity tend to co-vary during most stimulus manipulations (such as contrast modulations) or cognitive tasks (such as attentional modulation), it is difficult to dissociate these two hypotheses. We studied the relationship between high-gamma power, gamma rhythm, and spiking activity in the primary visual cortex (V1) of awake monkeys while varying the stimulus size, which increased the gamma power but decreased the firing rate, permitting a dissociation. We found that gamma power became anti-correlated with the high-gamma power, suggesting that the two phenomena are distinct and have different origins. On the other hand, high-gamma power remained tightly correlated with spiking activity under a wide range of stimulus manipulations. We studied this relationship using a signal processing technique called Matching Pursuit and found that action potentials are associated with sharp transients in the LFP with broadband power, which is visible at frequencies as low as ～50 Hz. These results distinguish broadband high-gamma activity from gamma rhythms as an easily obtained and reliable electrophysiological index of neuronal firing near the microelectrode. Further, they highlight the importance of making a careful dissociation between gamma rhythms and spike-related transients that could be incorrectly decomposed as rhythms using traditional signal processing methods.     

Increase trend of correlation and phase synchrony of microwire iEEG before macroseizure onset

Micro/macrowire intracranial EEG (iEEG) signals recorded from implanted micro/macroelectrodes in epileptic patients have received great attention and are considered to include much information of neuron activities in seizure transition compared to scalp EEG from cortical electrodes. Microelectrode is contacted more close to neurons than macroelectrode and it is more sensitive to neuron activity changes than macroelectrode. Microwire iEEG recordings are inevitably advantageous over macrowire iEEG recordings to reveal neuronal mechanisms contributing to the generation of seizures. In this study, we investigate the seizure generation from microwire iEEG recordings and discuss synchronization of microwire iEEGs in four frequency bands: alpha (1−30 Hz), gamma (30−80 Hz), ripple (80–250 Hz), and fast ripple (>250 Hz) via two measures: correlation and phase synchrony. We find that an increase trend of correlation or phase synchrony exists before the macroseizure onset mostly in gamma and ripple bands where the duration of the preictal states varied in different seizures ranging up to a few seconds (minutes). This finding is contrast to the well-known result that a decrease of synchronization in macro domains exists before the macroseizure onset. The finding demonstrates that it is only when the seizure has recruited enough surrounding brain tissue does the signal become strong enough to be observed on the clinical macroelectrode and as a result support the hypothesis of progressive coalescence of microseizure domains. The potential ramifications of such an early detection of microscale seizure activity may open a new window on treatment by making possible disruption of seizure activity before it becomes fully established.     

Functional aspects of evoked alpha and theta responses in humans and cats

A systems theoretical approach was used to compare possible functional roles of theta (4--7 Hz) and alpha (8--15 Hz) response components of brain evoked potentials. These response components were described earlier by Ba\c sar (1980). We recorded EEG and evoked potentials (EPs) from occipital scalp locations in 11 subjects. We used auditory and visual stimuli as inadequate and adequate stimuli, respectively (``cross-modality' measurements). The combined EEG-EP epochs were analysed in frequency domain with fast Fourier transform and adaptive digital filters. Alpha (8--15 Hz) response components turned out to be dependent on whether the stimulus was adequate or not (median amplitude with inadequate vs. adequate stimulation: vs. ). Theta (4--7 Hz) response components were less dependent on stimulus modality (inadequate vs. adequate stimulation: vs. ). In EP recordings the occipital alpha response almost disappeared in the first 250 ms following auditory stimulation. Comparable behaviour was observed in similar experiments with recordings from the cat visual cortex (area 17) and with occipital magnetoencephalographic recordings. Taking into account the above-mentioned previous reports on intracranial recordings in primary sensory areas of the cat brain and preliminary results of magnetoencephalographic measurements, we propose the following hypothesis: alpha responses in a time window of about 250 ms after stimulation might predominantly reflect primary sensory processing whereas the theta responses in the first 250 ms after stimulation might be more involved in supra-modality -- or cross-modality -- associative-cognitive processing. Received: 25 February 1994 / Accepted in revised form: 5 August 1994     

Principles of the 2-deoxyglucose method for the determination of the local cerebral glucose utilization

Sokoloff and co-workers developed the 2-deoxy-D-[1-14C]glucose (2DG) method in order to study the local cerebral glucose utilization (LCGU) of discrete brain regions in vivo. Energy metabolism of the adult mammalian brain is almost entirely dependent on glucose. The majority of the glucose taken up by the brain is needed for the maintenance of the membrane potentials and the electrical activity. The functional activity could thus be shown to be closely linked to energy metabolism. Consequently, examination of the energy metabolism by measuring the cerebral metabolic rate for glucose can provide information concerning functional activity in all of the neuroanatomically defined regions of the brain. Studying the fate of experimentally injected 2-deoxy-D-[1-14C]glucose, a radioactive labeled analogue of glucose, and, subsequently, employing quantitative autoradiographic techniques, it is possible to estimate the levels of the local cerebral glucose utilization in specific regions of the brain. According to Sokoloff (1982) the LCGU represents a "metabolic encephalography".     

Effects of isolated and combined exposures to whole-body vibration and noise on auditory-event related brain potentials and psychophysical assessment

Auditory event-related brain potentials (ERP) in response to two different tone stimuli (1.1 kHz or 1 kHz, 80 dB, 50 ms; given by headphones at a regular interstimulus interval of 5 s with a probability distribution of 70:30) were recorded from 12 healthy male subjects (Ss) during four different conditions with two repetitions: A-60 dBA white noise (wN), no whole-body vibration (WBV); B-60 dBA wN plus sinusoidal WBV in the az-direction with a frequency of 2.01 Hz and acceleration of 2 m.s-2 root mean square; C-80 dBA wN, no WBV; D-80 dBA wN plus WBV. Each condition consisted of two runs of about 11 min interrupted by a break of 4 min. During the break with continuing exposure, but without auditory stimuli, Ss judged the difficulty of the tone-detection task and intensity of noise by means of cross-modality matching (CMM). Vibration-synchronous activity in the electrocardiogram was eliminated by a subtraction-technique. Noise caused an attenuation of the N1 and P2 amplitudes and prolongation of P3 latencies. The WBV did not cause systematic ERP effects. Condition B was associated with higher N1 and smaller P3 amplitudes. The factor "condition" had a significant effect on the peak latencies of P3 to target stimuli and the task difficulty judged by CMM. Both effects exhibited significant linear increases in the sequence of conditions A, B, C, D. For the evaluation of exposure conditions at work, it can be suggested that noise has a strong systematic effect which can be enhanced by WBV.(ABSTRACT TRUNCATED AT 250 WORDS)     

Continuity and prospects of development of researches in area system-integrativity of psychophysiology of functional state and cognitive activity

In the review one of actual problems of psychophysiology in studying a phenomenon of integration of mechanisms of regulation of state of a brain and features of the organization is discussed by a brain of cognitive activity. Basic value of results of long-term researches of academician N.P. Bechterevoj and of her school is opened in the field of neurophysiology of functional states as bases of the organization of mental activity in conditions of direct, long and sparing contact to a cortical and subcortical structures of a brain, with the help long-term intracerebral electrodes. Arguments about a commensurability and complementary value similar on amplitud-time parameters slow and superslow gradual changes of neurophysiological processes registered simultaneously in identified zones of subcortical structures of a brain and with removal from a surface of a head in cortical projections of basic integrativity of the centres are submitted. Representations about a brain as difficultly organized "swimming" many-contour, neurodinamic informational-controlling suprasystem with hierarchically, probability a principle of the organization different on speeds and intensity of processes of the ability to live participating in maintenance of a condition of rest, mental conditions and cognitive activity are formulated and argued. At the limited set universal neurodinamic "languages", the brain has the multiregister mechanism of regulation of conditions and selectivity of mechanisms of the integration providing the contribution differing on information maintenance gradual neurophysiological of processes of different levels of the structurally functional organization in formation of brain systems of maintenance of concrete kinds of cognitive activity.     

Rapid biphasic arteriolar dilations induced by skeletal muscle contraction are dependent on stimulation characteristics

To test the hypothesis that measurable changes in microvasculature dilation occur in response to a single short-duration tetanic contraction, we contracted three to five skeletal muscle fibres of the hamster cremaster muscle microvascular preparation (in situ) and evaluated the response of an arteriole overlapping the active muscle fibres. Arteriolar diameter (baseline diameter = 16.4 +/- 0.9 micro m, maximum diameter = 34.7 +/- 1.2 micro m) was measured before and after a single contraction resulting from a range of stimulus frequencies (4, 10, 20, 30, 40, 60, and 80 Hz) within a 250- or 500-ms train. Four and 10 Hz produced a significant dilation at 2.9 +/- 0.4 and 6.5 +/- 2.8 s, respectively, within a 250-ms train and 3.0 +/- 0.2 and 6.1 +/- 1.3 s, respectively, within a 500-ms train. Biphasic dilations were observed within a 250-ms train at 20 Hz (at 3.9 +/- 0.9 and 22.1 +/- 4.3 s), 30 Hz (at 2.7 +/- 0.3 and 17.5 +/- 2.9 s), and 40 Hz (at 3.8 +/- 0.4 and 23.2 +/- 2.6 s) and within a 500-ms train at 20 Hz (at 4.8 +/- 0.4 and 31.9 +/- 3.8 s) and 30 Hz (at 3.4 +/- 0.3 and 27.6 +/- 3.0 s). A single dilation was observed within a 250-ms train at 60 Hz (at 5.1 +/- 0.7 s) and 80 Hz (at 14.2 +/- 3.3 s) and within a 500-ms train at 40 Hz (at 9.9 +/- 3.2 s), 60 Hz (at 7.9 +/- 2.1 s), and 80 Hz (at 13.4 +/- 4.0 s). We have shown that a single contraction ranging from a single twitch (4 Hz, 250 ms) to fused tetanic contractions produces significant arteriolar dilations and that the pattern of dilation is dependent on the stimulus frequency and train duration.     

A new look at gamma? High- (>60 Hz) γ-band activity in cortical networks: function, mechanisms and impairment

γ-band oscillations are thought to play a crucial role in information processing in cortical networks. In addition to oscillatory activity between 30 and 60 Hz, current evidence from electro- and magnetoencephalography (EEG/MEG) and local-field potentials (LFPs) has consistently shown oscillations >60 Hz (high γ-band) whose function and generating mechanisms are unclear. In the present paper, we summarize data that highlights the importance of high γ-band activity for cortical computations through establishing correlations between the modulation of oscillations in the 60-200 Hz frequency and specific cognitive functions. Moreover, we will suggest that high γ-band activity is impaired in neuropsychiatric disorders, such as schizophrenia and epilepsy. In the final part of the paper, we will review physiological mechanisms underlying the generation of high γ-band oscillations and discuss the functional implications of low vs. high γ-band activity patterns in cortical networks.     

Large-Scale,High-Resolution Multielectrode-Array Recording Depicts Functional Network Differences of Cortical and Hippocampal Cultures

Understanding the detailed circuitry of functioning neuronal networks is one of the major goals of neuroscience. Recent improvements in neuronal recording techniques have made it possible to record the spiking activity from hundreds of neurons simultaneously with sub-millisecond temporal resolution. Here we used a 512-channel multielectrode array system to record the activity from hundreds of neurons in organotypic cultures of cortico-hippocampal brain slices from mice. To probe the network structure, we employed a wavelet transform of the cross-correlogram to categorize the functional connectivity in different frequency ranges. With this method we directly compare, for the first time, in any preparation, the neuronal network structures of cortex and hippocampus, on the scale of hundreds of neurons, with sub-millisecond time resolution. Among the three frequency ranges that we investigated, the lower two frequency ranges (gamma (30–80 Hz) and beta (12–30 Hz) range) showed similar network structure between cortex and hippocampus, but there were many significant differences between these structures in the high frequency range (100–1000 Hz). The high frequency networks in cortex showed short tailed degree-distributions, shorter decay length of connectivity density, smaller clustering coefficients, and positive assortativity. Our results suggest that our method can characterize frequency dependent differences of network architecture from different brain regions. Crucially, because these differences between brain regions require millisecond temporal scales to be observed and characterized, these results underscore the importance of high temporal resolution recordings for the understanding of functional networks in neuronal systems.     

Multiple origins of the cortical γ rhythm

Gamma rhythms (30-80 Hz) are a near-ubiquitous feature of neuronal population activity in mammalian cortices. Their dynamic properties permit the synchronization of neuronal responses to sensory input within spatially distributed networks, transient formation of local neuronal "cell assemblies," and coherent response patterns essential for intercortical regional communication. Each of these phenomena form part of a working hypothesis for cognitive function in cortex. All forms of physiological gamma rhythm are inhibition based, being characterized by rhythmic trains of inhibitory postsynaptic potentials in populations of principal neurons. It is these repeating periods of relative enhancement and attenuation of the responsivity of major cell groups in cortex that provides a temporal structure shared across many millions of neurons. However, when considering the origins of these repeating trains of inhibitory events considerable divergence is seen depending on cortical region studied and mode of activation of gamma rhythm generating networks. Here, we review the evidence for involvement of multiple subtypes of interneuron and focus on different modes of activation of these cells. We conclude that most massively parallel brain regions have different mechanisms of gamma rhythm generation, that different mechanisms have distinct functional correlates, and that switching between different local modes of gamma generation may be an effective way to direct cortical communication streams. Finally, we suggest that developmental disruption of the endophenotype for certain subsets of gamma-generating interneuron may underlie cognitive deficit in psychiatric illness.