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PubMed2003

Synchronization tomography: a method for three-dimensional localization of phase synchronized neuronal populations in the human brain using magnetoencephalography.

We present a noninvasive technique which allows the anatomical localization of phase synchronized neuronal populations in the human brain with magnetoencephalography. We study phase synchronization between the reconstructed current source density (CSD) of different brain areas as well as between the CSD and muscular activity. We asked four subjects to tap their fingers in synchrony with a rhythmic tone, and to continue tapping at the same rate after the tone was switched off. The phase synchronization behavior of brain areas relevant for movement coordination, inner voice, and time estimation changes drastically when the transition to internal pacing occurs, while their averaged amplitudes remain unchanged. Information of this kind cannot be derived with standard neuroimaging techniques like functional magnetic resonance imaging or positron emission tomography.

Brain↗
PubMed1999

Mechanisms of neural synchrony in the septohippocampal pathways underlying hippocampal theta generation.

Using urethane-anesthetized rats, 18 simultaneously recorded septohippocampal cell pairs (36 individual cells), each classified as theta-related according to the criteria of, were studied during four spontaneously occurring hippocampal field conditions: (1) large amplitude irregular activity (LIA) only; (2) the transition from LIA to theta; (3) theta only; and (4) the transition from theta to LIA. The main objective was to study the temporal relationships and degree of neural synchrony between the discharges of the cell pairs, using both time-averaged and time-dependent joint peristimulus time histogram correlation techniques, during the four conditions, to determine their contribution to the control of oscillation and synchrony (theta) in the hippocampus. The study demonstrated that the transition from the LIA state to the theta field state in the hippocampus required a temporal sequence of changes in theta-related cellular activity occurring on average 500 msec preceding the transition: (1) the medial septum inhibits hippocampal theta-OFF cells; (2) medial septal tonic theta-ON cells provide tonic depolarizing inputs to initiate membrane potential oscillations (MPOs) in hippocampal phasic theta-ON cells, whereas medial septal phasic theta-ON cells synchronize the MPOs of hippocampal phasic theta-ON cells and the discharges of hippocampal tonic theta-ON cells. Much of the time preceding the LIA to theta transition is accounted for by recruitment of these theta-related cell populations. Conversely, "turning off" the theta state occurs abruptly and involves the medial septal disinhibition of hippocampal theta-OFF cells.

Animals↗
PubMed1976

[Effect of the prolonged use of streptomycin as well as streptomycin in combination with tubazid on the bioelectrical activity of the brain in experimental tuberculosis].

The effect of streptomycin used alone and in combination with tubazid on the brain electric activity was studied in chronic experiments on rabbits with tuberculosis. The electrocorticographical investigations showed that the antibacterial treatment lowered the spontaneous electric activity and reactive capacity of the cortex. It was evident from a narrow amplitude of the main rythm, coefficient and energy of synchronization on rythmic photostimulation and paroxysmal activity withing the theta range. With the account of the high therapeutic effect of the antibacterial treatment evident from minimum affection of the organs with tuberculosis, the above changes in the electrocorticogrammes should be attributed to the neurotropic effect of the drug and not to tuberculosis intoxication.

Alpha Rhythm↗
PubMed1998

[Characteristics and mechanisms of the interhemisphere synchronization in the rat motor cortex].

Synchronised activity of the callosal cells was studied in the rat motor cortex. Cross-correlation analysis revealed narrow symmetrical peaks (less than 20 ms) and intermediate ones (30-80 ms). Common neuron(s) located in one hemisphere reciprocally connected callosal cells can play the role of a "common input" that synchronises discharges of the cells in both hemispheres. The narrow and intermediate peaks seem to be mediated by mono- and polysynaptic connections, resp.

Action Potentials↗
PubMed1991

Functional hemispherectomy: EEG findings, spiking from isolated brain postoperatively, and prediction of outcome.

We reviewed the prognostic significance of preoperative EEG findings in 25 patients who underwent functional hemispherectomy. Bilateral independent epileptogenic foci, found in five patients, generally indicate a less satisfactory outcome, with only three of the five patients becoming seizure free following hemispherectomy. In contrast, abnormalities of background activity over the "good" hemisphere, multifocal epileptic activity confined to the side of operation, or bilaterally synchronous discharges were associated with a good outcome and should not be considered as contraindications to operation. Postoperatively, discharges may occur in the functionally isolated frontal and occipital cortex, which are benign, with no other clinical significance than showing that the isolated cortex remains viable and continues to generate epileptogenic potentials.

Action Potentials↗
PubMed2006

Functional changes in the activity of cerebellum and frontostriatal regions during externally and internally timed movement in Parkinson's disease.

We used fMRI to investigate the neurofunctional basis of externally and internally timed movements in Parkinson's disease (PD) patients. Ten PD patients whose medication had been withheld for at least 18h and 11 age- and sex-matched healthy controls were scanned while performing continuation paradigm with a visual metronome. Compared with the controls, PD patients displayed an intact capability to store and reproduce movement frequencies but with a significantly increased movement latencies. No differences in BOLD response were found in both groups when comparing the continuation with the preceding synchronization phase and viceversa, except for activity in visually related regions. Relative to healthy controls during the synchronization phase, PD patients exhibited an overall signal increase in the cerebellum and frontostriatal circuit (putamen, SMA and thalamus) activity together with specific brain areas (right inferior frontal gyrus and insula cortex) that are also implicated in primary timekeeper processes. By contrast, in the continuation phase the only neural network involved to a greater extent by the PD group was the cerebello-thalamic pathway. The lack of neurofunctional differences between the two timing phases suggests that rhythmic externally and internally guided movements engage similar neural networks in PD and matched healthy controls. Moreover, between-group comparison indicates that PD patients OFF medication may compensate for their basal ganglia-cortical loop's dysfunction using different motor pathways involving cerebellum and basal ganglia relays during the two phases of rhythmic movement.

Adult↗
PubMed2004

Phase relationships between different subdural electrode recordings in man.

Almost all brain-computer interfaces (BCIs) ignore information related to the phase coupling between electroencephalogram (EEG) or electrocorticogram (ECoG) recordings from different electrodes. This paper investigates whether additional information can be found when calculating the amount of synchronization between two electrode channels by using a phase locking measurement called the phase locking value (PLV). Special emphasis is put on the beta band (around 20 Hz) as well as the gamma band (high frequencies up to 95 Hz), which can only be used when subdural electrode recordings are available.

Action Potentials↗
PubMed1999

Perception's shadow: long-distance synchronization of human brain activity.

Transient periods of synchronization of oscillating neuronal discharges in the frequency range 30-80 Hz (gamma oscillations) have been proposed to act as an integrative mechanism that may bring a widely distributed set of neurons together into a coherent ensemble that underlies a cognitive act. Results of several experiments in animals provide support for this idea. In humans, gamma oscillations have been described both on the scalp (measured by electroencephalography and magnetoencephalography) and in intracortical recordings, but no direct participation of synchrony in a cognitive task has been demonstrated so far. Here we record electrical brain activity from subjects who are viewing ambiguous visual stimuli (perceived either as faces or as meaningless shapes). We show for the first time, to our knowledge, that only face perception induces a long-distance pattern of synchronization, corresponding to the moment of perception itself and to the ensuing motor response. A period of strong desynchronization marks the transition between the moment of perception and the motor response. We suggest that this desynchronization reflects a process of active uncoupling of the underlying neural ensembles that is necessary to proceed from one cognitive state to another.

Adult↗
PubMed2004

Organization of interlaminar interactions in the rat superior colliculus.

Our previous studies have shown that when slices of the rat superior colliculus (SC) are exposed to a solution containing 10 microM bicuculline and a low concentration of Mg2+ (0.1 mM), most neurons in the intermediate gray layer (stratum griseum intermediale; SGI), wide-field vertical (WFV) cells in the optic layer (stratum opticum; SO), and a minor population of neurons in the superficial gray layer (stratum griseum superficiale; SGS) exhibit spontaneous depolarization and burst firing, which are synchronous among adjacent neurons. These spontaneous and synchronous depolarizations were thought to share common mechanisms with presaccadic burst activity in SGI neurons. In the present study, we explored the site responsible for generation of synchronous depolarization of SGI neurons by performing dual whole cell recordings under different slice conditions. A pair of SGI neurons recorded in a small rectangular piece of the SGI punched out from the SC slice showed synchronous depolarization but far less frequently than those recorded in a small rectangular piece including SGS and SO. This suggests that the superficial layers are needed for triggering synchronous depolarization in the SGI. Furthermore, we recorded spontaneous depolarizations in pairs of neurons belonging to the different layers. Analysis of their synchronicity revealed that WFV cells in the SO exhibit synchronous depolarizations with both SGS and SGI neurons, and the onset of spontaneous depolarization in WFV cells precedes those of neurons in other layers. Further, when SGS and SGI neurons exhibit synchronous depolarizations, SGI neurons usually precede the SGS neurons. These observations give further evidence to the existence of interlaminar interaction between superficial and deeper layers of the SC. In addition, it is suggested that WFV cells can trigger burst activity in other layers of the SC and that there is an excitatory signal transmission from the deeper layers to the superficial layers.

Animals↗
PubMed2004

Blockage of vibrissal afferents: III. Electrocorticographic effects.

We have shown signs of behavioral depression after vibrissal deafferentation. Locomotor slowing, motor impairments and footshock thresholds increment were demonstrated after vibrissal afferent blockages. Here, we study the electrocortical (ECoG) effects of vibrissal pad anaesthesia, also replicated by bilateral brachial plexus blockage. We found in both cases, that this acute and massive deafferentation produces synchronization over the entire neocortex accompanied by an important loss of muscular electrical activity. Slow waves observed in this condition were similar to those recorded in the sleeping rat without any treatment, but in our case, there were no behavioral signs of sleep. Thus a clear behavioral electroencephalographic dissociation was obtained by acute deafferentation. These results would seem to support the sleep deafferentation hypothesis.

Afferent Pathways↗
PubMed2004

Local and remote functional connectivity of neocortex under the inhibition influence.

The current paper focuses on a relatively new and promising area of the study of EEG transformations during brain information processing based on the reduction of the signal to the discrete quasi-stationary segment sequences which may reflect individual brain microstates or discrete operations. In this framework, the complex brain functions require integration of several operations throughout the whole neocortex. However, the role of inhibitory brain systems in such processes is still unsettled. The effects of a single dose (30 microg/kg) of lorazepam on the operational activity of neuronal populations and on the temporal binding between them were examined in a double-blind randomized crossover placebo-controlled study with eight healthy volunteers. EEG measures at 20 channels were evaluated on two occasions: (1) eyes closed, (2) eyes open. In short, we conducted a two-by-two factorial study where one factor manipulated GABAergic neurotransmission (lorazepam vs. placebo), and the other factor was simply brain state (eyes closed vs. eyes opened). We were primarily interested in the main effect of lorazepam. In the present study, a connection between the mesoscopic level, described by the local functional processes (neuronal assemblies or populations) and the macroscopic level, described as a sequence of metastable brain states (remote functionally synchronized neuronal populations) was established. The role of inhibitory brain systems facilitated by lorazepam in the operational dynamics of neuronal populations and in the process of EEG structural synchrony (SS) (topological peculiarities) was addressed for the first time. It was shown that GABA signaling reorganized the dynamics of local neuronal populations and the remote functional connectivity between them.

Adult↗
PubMedDate not supplied

Connection topology dependence of synchronization of neural assemblies on class 1 and 2 excitability.

Two main classes of excitable neurons are analyzed in terms of connection topology and strength of the coupling in a network of neurons. In both cases, we measure the degree of synchronization and responsiveness of the neural assembly. Class 2 excitability presents a fast wave-like propagation of the activity pattern, strong frequency dependence on the connection topology and a good level of synchronization regardless of the topology. On the other hand, class 1 excitability shows a strong dependence of the wave propagation speed and the synchronization degree on the connection topology, in addition no frequency adaptation is observed. We conclude that both types of neural excitability endow the neural assembly with very different dynamical properties. Although, for simplicity reasons, no inhibition has been included in our study, the emergent properties described in this paper may help to determine the class of excitability underlying a neural assembly.

Action Potentials↗
PubMedDate not supplied

[Superslow oscillations of the indices of the state of a human-operator as a result of monotony].

Infralow oscillations were studied of psychophysiological parameters appearing at one-minute wave range at different levels of human operator's nervous system in conditions of monotony. In experiments on recognition of noisy visual images presented with the frequency of 6-9 signals per hour, 22 subjects took part. The following was found: a) correlation between superslow components of pulse rate and the coefficient of brain potentials synchronization, established in 20-30 min after the beginning of the experiment; b) a tendency to deterioration of the quality of recognition at the stages of slowing down of infralow waves of the pulse rate and to its improvement at the phases of the increase of their frequency. Main results were obtained by the method which needs neither unartifact electrodes nor DC amplifiers. Possible mechanisms of stated dependences are discussed.

Adaptation, Psychological↗
PubMedDate not supplied

[Modeling different regimes of bioelectrical activity in the brain in normal subjects and in "increased readiness" in a network of neuron-like elements].

Desynchronous (low voltage fast activity), synchronous (high voltage slow waves) as well as convulsive brain activities were stimulated by a computer model of neuronal population. Network excitatory and inhibitory elements possessed fundamental dynamic properties of real neurones. Being independent both of the excitability of elements and of external influence efficacy, synchronous (desynchronous) network activity resulted from the increase (decrease) of the average power of "neuronal" interconnections which imitated mutual and recurrent excitation and inhibition. The inhibition efficacy being reduced as compared with excitation, synchronization of elements became intensified. As a consequence, the rhythmic activity amplitude increased and the appearance of self-sustained oscillations simulating convulsive activity was facilitated. The probable mechanism of EEG activation by virtue of the reduction of mutual and recurrent excitation and inhibition efficacy as well as the significance of inhibitory mechanism deficiency for epileptogenesis are discussed.

Brain↗
PubMed2006

Interaction dynamics of neuronal oscillations analysed using wavelet transforms.

This paper describes the use of a computational tool based on the Morlet wavelet transform to investigate the interaction dynamics between oscillations generated by two anatomically distinct neuronal populations. The tool uses cross wavelet transform, coherence, bi-spectrum/bi-coherence and phase synchronization. Using specimen data recorded from the hippocampus of a rat with experimentally induced focal epilepsy, linear and non-linear correlations between neuronal oscillations in the CA1 and CA3 regions have been computed. The results of this real case study show that the computational tool can successfully analyse and quantify the temporal interactions between neuronal oscillators and could be employed to investigate the mechanisms underlying epilepsy.

Animals↗
PubMedDate not supplied

[Spatial-temporal synchronization of cerebral biopotentials and the problem of the brain's activity as a whole].

The author compares the results of his own investigations into the influence of instantaneous and multiple reversible (cold) inactivation of the neocortex on the manifestation and elaboration of conditioned reflexes in cats with dynamic characteristics of spatial-temporal synchronization of biopotentials in the cortex and subcortical formations at different stages of formation and manifestation of the conditioned reflex in animals, and in different functional states (emotions and mental stress) in humans, as presented in the studies by M.N. Livanov and coworkers. It has been stressed that different experimental approaches reveal the one principle of brain functioning, its integral involvement in any purposeful activity.

Animals↗
PubMed2003

Trait anxiety impact on the EEG theta band power changes during appraisal of threatening and pleasant visual stimuli.

The main objective of the present investigation was to examine whether trait anxiety construct would influence EEG event-related synchronization (ERS) of the theta power during viewing of visual threatening stimuli. The 62-channel EEG was recorded while low (LA, n= 18) and high (HA, n= 18) trait-anxious subjects viewed sequentially presented neutral, threatening and pleasant pictures. Between-group differences, related to stimulus emotionality, were linked to the test period of 0-1000 ms after stimulus onset. In the low theta (4-6 Hz) at prefrontal sites HA exhibited deficient ERS in response to both threatening and pleasant stimuli in the right hemisphere, whereas LA yielded larger right than left hemisphere ERS in response to all the three stimulus categories. In the upper theta (6-8 Hz) group differences were associated with posterior cortical regions: HA exhibited the largest ERS to threatening and the lowest to pleasant stimuli, whereas LA prompted the largest ERS to pleasant and the lowest to neutral pictures. It is suggested that low theta right prefrontal hypoactivation favoring left hemispheric (i.e. more analytical) activity along with higher upper theta ERS of posterior cortical regions (i.e. enhanced higher order visual processing) to threatening stimuli could form the basis for neuropsychologically observed general bias towards threatening information in HA.

Adolescent↗
PubMed1999

Event-Related changes of band power and coherence: methodology and interpretation.

Event-related calculation of band power changes can be used to quantify event-related desynchronization, event-related synchronization, and event-related coherence (ERCoh). It is shown that in the case of a motor task especially, the ERCoh time course depends on the type of EEG derivation used, whereby referenced EEG data can result in a bilateral coherence increase, although both hemispheres generate independent sensorimotor rhythms. It is further shown that not only Rolandic mu rhythms but also central beta rhythms display a lack of interhemispheric linear phase coupling.

Alpha Rhythm↗