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PubMed2006

Precise long-range synchronization of activity and silence in neocortical neurons during slow-wave oscillations [corrected].

Slow-wave sleep is characterized by alternating periods of activity and silence in corticothalamic networks. Both activity and silence are stable network states, but the mechanisms of their alternation remain unknown. We show, using simultaneous multisite intracellular recordings in cats, that slow rhythm involves all neocortical neurons and that both activity and silence started almost synchronously in cells located up to 12 mm apart. Activity appeared predominantly at the area 5/7 border and spread in both anterior and posterior directions. The activity started earlier in fast-spiking cells and intrinsically bursting cells than in regular-spiking neurons. These results provide direct evidence for two mechanisms of active state generation: spread of activity from a local focus and synchronization of weaker activity, originating at multiple locations. Surprisingly, onsets of silent states were synchronized even more precisely than the onsets of activity, showing no latency bias for location or cell type. This most intriguing finding exposes a major gap in understanding the nature of state alternation. We suggest that it is the synchronous termination of activity and occurrence of silent states of the neuronal network that makes the EEG picture during slow-wave sleep so characteristic. Synchronous onset of silence in distant neurons cannot rely exclusively on properties of individual cells and synapses, such as adaptation of neuronal firing or synaptic depression; instead, it implies the existence of a network mechanism. Revealing this yet unknown large-scale mechanism, which switches network activity to silence, will aid our understanding of the origin of brain rhythms in normal function and pathology.

Action Potentials↗
PubMed2002

Beta electroencephalograph changes during passive movements: sensory afferences contribute to beta event-related desynchronization in humans.

Non-phase-locked beta oscillatory changes during passive movements were studied in six healthy volunteers, and compared with those observed in a similar group during ballistic movements. Passive movements consisted of brisk wrist extensions done with the help of a pulley system. Changes in the beta band were determined by means of wavelet and Gabor transforms, and compared statistically with a pre-movement period. In this paradigm, a marked beta energy loss (event-related desynchronization, ERD) was present after the beginning of the movement, followed by a beta energy increase (event-related synchronization, ERS). The ERD/ERS was similar to that observed during ballistic movements, but without pre-movement components. Although both changes were maximal in the contralateral central electrode, the beta ERD showed a more bilateral topography. These findings suggest that afferent proprioceptive inputs may play a role in the final part of the beta ERD observed during voluntary movements.

Adult↗
PubMed2004

Synchronization of neural oscillations as a possible mechanism underlying episodic memory: a study of theta rhythm in the hippocampus.

Rat hippocampal cells exhibit characteristic phase-dependent firings when oscillation in frequency range around 8Hz is present. Based on the hypothesis that theta phase coding is generated by synchronization of neural activities, an autoassociative network model of the hippocampus and the entorhinal cortex was analyzed to explore mechanisms underlying episodic memory. Phase coding in theta rhythm enables instantaneous acquisition of experienced events including temporal and spatial contents. Further comparison with electrophysiological data from both rodents and primates suggests a possible role of theta oscillations in memory encoding and online processing of episodic events.

Action Potentials↗
PubMed1986

[Electroencephalographic correlates of positive emotional reactions in children in the first year of life].

The authors investigated electroencephalographic correlates of positive emotional reactions in 28 infants aged from 3 to 10 months. An analysis of the space organization of the hypersynchronous 4 Hz frequency theta-rhythm attending emotional reactions has shown that depending on the type of impact, neural elements in the anterior or posterior cerebral cortex synchronously come into play. It is assumed that the arrangement of the above type of activity is due to both nonspecific activation of the cortex through the influence of the subcortical structures and due to the mechanisms of local activation becoming involved in the realization of the response depending on the biological quality of the irritant and the nature of the activity induced by it.

Action Potentials↗
PubMed1975

[Influence of the anterior and posterior hypothalamus on the conditioned reflex activity and delayed responses of lower simians].

In 4 adult monkeys, electrical stimulation of the anterior hypothalamus followed by subsidence in the animal and the ECoG synchronization evoked also an impairment of conditioned reflex activity and a decrease in the test performance during delayed responses. Strong stimulation of the posterior hypothalamus followed by emotional arousal and desynchronization in the ECoG, on the contrary, improved the conditioned reflex activity and increased the level of the test performance. The hypothalamus is then supposed to play a certain role in memory as an emotiogenic structure.

Animals↗
PubMed2004

Contribution of different EEG frequencies to auditory evoked potential abnormalities in schizophrenia.

OBJECTIVE: We have shown previously [Clin Neurophysiol 2003;114:79] that phase reorganization of the ongoing electroencephalogram (EEG) plays an important role in the generation of auditory evoked potential (EP) components with a latency between 50 and 200 ms. In the present study, we investigate whether schizophrenia patients suffer from phase synchronization deficits as compared to normal subjects. METHODS: The auditory EPs from 20 normal subjects and 19 schizophrenia patients were analyzed. EPs were obtained using a double stimulus paradigm, in which two identical tone bursts (S1 and S2) were delivered with an average inter-stimulus interval of 500 ms and an inter-pair interval of 8 s. The Piecewise Prony Method (PPM) was used to decompose single trial auditory evoked potentials into different frequency bands. Pre- and post-stimulus phase histograms were compared for each frequency band to determine the degree of phase synchronization produced by auditory stimulation in the two populations. RESULTS: The S1 stimulus produced significantly less (P < 0.05) phase synchronization in schizophrenia patients than in normal subjects in the 2-12 Hz frequency range. Far fewer and smaller inter-population phase synchronization differences were seen for the S2 stimulus. Both populations showed more phase synchronization for S1 than S2. A significant correlation (P < 0.01) between N100 amplitude and phase synchronization 100 ms post S1 was observed for the normal population but not for the schizophrenia group. The correlation between P200 amplitude and phase synchronization 200 ms post S1 was significant for the normal group (P < 0.01) and the schizophrenia group (P < 0.03). CONCLUSIONS: Schizophrenia patients have a phase synchronization deficiency, as compared to a normal control group, especially for the first stimulus, in the 2-12 Hz frequency range. This deficiency explains the lower EP amplitudes and may be a significant factor contributing to reduced sensory gating reported in schizophrenic subjects. SIGNIFICANCE: The research presented here contributes to the understanding of the mechanism underlying sensory gating in health and gating deficiencies in schizophrenia.

Acoustic Stimulation↗
PubMed2001

Theta-rhythmically firing neurons in the anterior thalamus: implications for mnemonic functions of Papez's circuit.

In 1937 Papez described an anatomical circuit (or loop) beginning and ending in the hippocampal formation that he proposed subserved emotional experience (Papez, 1937). Specifically, the projections of the circuit were as follows: hippocampal formation--> mammillary bodies--> anterior thalamus--> cingulate cortex--> parahippocampal gyrus--> hippocampal formation. Although the circuit has been refined based on subsequent anatomical findings (Amaral and Witter, 1995; Shibata, 1992; Van Groen and Wyss, 1995), the major links of the circuit unquestionably represent a prominent system of connections in the mammalian brain. Hence, the enduring nature of 'Papez's circuit'. Unlike, however, its persistence as anatomical entity, the proposed functional role for the circuit has been less resilient. The early notion that Papez's circuit subserves emotional experience/expression has been abandoned (LeDoux, 1993) and replaced by the proposal that it is primarily involved in mnemonic functions (Aggleton and Brown, 1999). Lesions of each of the major components of the circuit have been shown to disrupt memory (Aggleton and Brown, 1999; Sutherland et al., 1988; Sziklas and Petrides, 1993). The mammillary bodies represent a major output from the hippocampus in Papez's circuit (Amaral and Witter, 1995). It has recently been shown that cells of mammillary body fire rhythmically in bursts synchronous with the theta rhythm of the hippocampus (Bland et al., 1995; Kirk et al., 1996; Kocsis and Vertes, 1994, 1997) and that this rhythmical activity is dependent upon the action of the hippocampus on the mammillary bodies (Bland et al., 1995; Kirk et al., 1996). It is well established that the mammillary bodies project massively to the anterior thalamus (Shibata, 1992), which taken together with the demonstration that mammillary body cells fire synchronously with theta, suggests that the mammillary bodies may act on the anterior thalamus, possibly in the manner that the hippocampus acts on the mammillary bodies, to rhythmically activate cells of the anterior thalamus at theta frequency. We demonstrated that approximately 75% of cells of the anterior ventral nucleus of the thalamus fire rhythmically synchronous with the hippocampal theta rhythm and the activity of 46% of these anterior ventral neurons was highly correlated with theta. These findings, together with demonstration of theta-rhythmically firing cells in other structures of Papez's circuit, indicate that a theta-rhythmic signal may resonate throughout Papez's circuit, possibly involved in the control of mnemonic functions of the circuit.

Action Potentials↗
PubMed1992

Vagal nerve stimulation in treatment of intractable partial seizures: nursing implications.

Seizures are the result of abnormal synchronization of electrical activity in the brain. Medical therapy is unsuccessful in controlling seizures for many patients with partial seizures and surgery may not be a viable option. An alternate mode of treatment of intractable partial seizures is needed. Vagal nerve stimulation is a treatment modality under investigation. Stimulating the vagus nerve is hypothesized to desynchronize cerebral electrical activity, yielding an antiepileptic effect. A multicenter vagal nerve stimulation study is currently underway.

Adolescent↗
PubMed2005

Sensorimotor transduction of time information is preserved in subjects with cerebellar damage.

The cerebellar contribution to motor entrainment through rhythmic auditory stimuli was analyzed by comparing rhythmic motor responses in subjects with cerebellar pathologies and in healthy controls. Eleven patients with cerebellar lesions and eight healthy subjects tapped in synchrony with an auditory rhythmic stimulus using a hand-held pencil-shaped electrode connected to a PC. A 60-stimulus sequence was delivered with an ISI of 500 ms and changed at random to a new ISI value with either consciously perceived (+/-50 ms) or unperceived tempo changes (+/-10 ms). Synchronization patterns for both groups were computed based on the timing of inter-response intervals (IRIs) and synchronization errors (SE). Variability of IRI as well as the timing of adaptation patterns after the tempo changes were modeled and analyzed mathematically using a logistic/sigmoid function. Healthy subjects performed with significantly lower IRI variability than cerebellar patients. Patients with focal lesions performed with significantly lower IRI variability than patients with atrophic lesions. Asymptote parameters during isochronous synchronization as well as slope angles and symmetry points of the adaptation curves after tempo perturbation showed no significant differences between groups. Present data indicate that temporal variability of rhythmic motor responses is differentially affected by distinct cerebellar pathologies but that motor entrainment to auditory rhythms is not affected by lesion of the cerebellar circuits.

Acoustic Stimulation↗
PubMedDate not supplied

[The influence of the Soviet antidepressants pyrazidol and inkazan on the effects of clonidine].

The influence of Soviet-made antidepressants pyrazidol and incazane on some clonidine-induced effects (hypolocomotion, reactions of synchronization and desynchronization in the EEG, aggression) were studied. Pyrazidol and incazane reduce the effects of low doses of clonidine--the hypolocomotor one and the synchronization reaction in the EEG and enhance the effects of a high dose of clonidine--aggression and the desynchronization reaction in the EEG. The reduction of the sedative effects of clonidine as well as the enhancement of its activating effects by antidepressants can reflect the activation of adrenergic transmission by them. The adrenopositive effect of pyrazidol and incazane is more pronounced that that of imipramine.

Aggression↗
PubMed2001

Spike timing, synchronization and information processing on the sensory side of the central nervous system.

To what extent is the variability of the neuronal responses compatible with the use of spike timing for sensory information processing by the central nervous system? In reviewing the state of the art of this question, I first analyze the characteristics of this variability with its three elements: synaptic noise, impact of ongoing activity and possible fluctuations in evoked responses. I then review the recent literature on the various sensory modalities: somato-sensory, olfactory, gustatory and visual and auditory processing. I emphasize that the conditions in which precise timing, at the millisecond level, is usually obtained, are conditions that usually require dynamic stimulation or sharp changes in the stimuli. By contrast, situations in which stimulation not belonging to the temporal domain is temporally encoded lead to much coarser temporal coding; although in both cases, neural networks transmit the signals with similarly high precision. Synchronization among neurons is an important tool in information processing in both cases but again seems to act either at millisecond or tens of millisecond levels. Information theory applied to both situations confirms that the average rate of information transmission is much higher in dynamic than in static situations. These facts suggest that channels of precise temporal encoding may exist in the brain but imply populations of neurons working in a yet to be discovered way.

Animals↗
PubMedDate not supplied

[Bursts of high-frequency synchronized electrical activity in the neocortex of dogs during food instrumental learning].

The EEG phenomenon was studied of high-frequency bursts (60-70 Hz, 70-80 mcV) in electrical activity of dog's neocortex (EA, 1-200 Hz) in the process of instrumental conditioning. These bursts of high-frequency oscillations appeared at the generalization state of the conditioned reflex during interstimulus intervals at the background of dominant EA of the lower frequency and voltage (10-40 mcV). Application of the developed by us novel strategy of the primary analysis of EA realizations (in particular, inhomogeneity coefficient) enabled estimation of the amplitude-frequency EA inhomogeneity, namely, high-frequency bursts. The regional peculiarities of the high-frequency bursts were revealed by means of the original technique based on the expansion of EA oscillation into a system of half-waves and construction of distribution maps on the basis of their parameters. The presented data verified our earlier findings obtained using other techniques (FFT analysis and factor analysis). These data testify to differential participation of cortical areas (even those which are close to each other within a distance of 3-5 mm) in the spatio-temporal organization of potentials characteristic for a given learning paradigm.

Animals↗
PubMedDate not supplied

Bursts of high-frequency synchronized electrical activity in the dog neocortex during food-related operant conditioning.

Bursts of high-frequency (HF, 80-90 Hz, 70-80 microV) oscillations in the electrical activity (EA, 1-200 Hz) of the dog neocortex were studied during operant conditioning. These bursts of HF oscillations appeared in the EA of interstimulus intervals at the generalization stage on a background of dominant oscillations of lower frequency and amplitude (10-40 microV). Use of a new strategy for primary analysis of EA production (specifically, a coefficient of inhomogeneity) allowed amplitude-frequency inhomogeneity of the EA to be estimated, with isolation of bursts of HF oscillations. Use of an original nonharmonic analysis, consisting of expansion of EA waves into a system of half-waves which were used to construct distribution maps, revealed the regional properties of bursts of HF oscillations. The results of these investigations supplement previous data obtained using other methodological approaches (Fourier transformation and spectral density factor analysis). The properties of bursts of HF oscillations observed here provide evidence for the differential involvement of cortical areas (even close-lying areas separated by distances of 3-5 mm) in the spatial-temporal organization of potentials typical of this conditioning paradigm.

Animals↗
PubMed1981

Genetic disposition to alcoholism. An EEG study in alcoholics and their relatives.

Family, twin, and adoption studies have shown that genetic factors are involved in the etiology of alcoholism. Based on earlier EEG findings in alcoholics and on the known genetic determination of the alcohol effect on the EEG, the hypothesis was tested whether the resting EEG reflects a certain disposition to alcoholism. Resting EEGs were examined for 115 alcoholics (78 males, 37 females) and matched controls. In addition, the first-degree relatives of two extreme groups of alcoholics--those with poor and those with particularly good alpha waves--were examined and compared with matched controls. The EEGs were analyzed with an EEG processor. Whereas male alcoholics did not differ from their controls, female patients showed a shift from the alpha and theta to the beta bands of the brain wave pattern. The relatives of the two extreme groups of alcoholics, who did not misuse alcohol, exhibited the same tendency. This is an argument supporting the notion that in females a poorly synchronized EEG pattern reflects a certain disposition to alcoholism. This finding is discussed in light of drinking motivation in males and females. The latter more often belong to the alpha- and gamma-types of alcoholism than do males. Because of comparable findings in schizophrenics it is argued that a genetically determined desynchronized resting EEG pattern is not specific for a certain illness, but reflects basic mechanisms that enhance the risk for different psychiatric disorders.

Adolescent↗
PubMedDate not supplied

Synchronization and cooperative interaction in brain activity.

A conception is advanced according to which synchronization and the cooperative interaction of plastic processes at the level of the individual cell and of cell units of varying degrees of complexity form a principle of cerebral integration. The triggering and unfolding of plastic reorganizations which take place with the participation of motivational-emotional structures are realized through the mechanism of alteration of cell excitability. These influences are widely distributed throughout the cerebral cortex, but are selective in relation to the current need of the organism.

Animals↗
PubMed2002

Neuroanatomical and neurophysiological consequences of strabismus: changes in the structural and functional organization of the primary visual cortex in cats with alternating fixation and strabismic amblyopia.

In recent years, evidence has accumulated indicating that long-ranging neuronal connections within the primary visual cortex (area 17) mediate the influences of context and experience, possibly also those of expectation. After early onset strabismus, the layout of these connections is massively modified: in strabismic but not in normally raised cats, horizontal connections extend primarily between neurons activated by the same eye. As a possible consequence of the modified circuitry, neuronal synchronization between different ocular dominance domains is also massively reduced. Thus, the inability of strabismics to combine the signals arriving from the two eyes into a single percept may be caused by these structural and functional changes. Strabismic amblyopia is also accompanied by significant modifications of intracortical associational interactions: corresponding to the psychophysical deficits, neurons driven by the normal eye displayed stronger synchronization of their responses than neurons dominated by the amblyopic eye.(1) These data demonstrated for the first time a clear neurophysiological correlate of strabismic amblyopia in area 17. They suggest that - similar to our observations in divergent squinters - at least some of the perceptual deficits of amblyopic patients are due to experience-dependent changes in intracortical circuitry. We analyze this question by combining optical imaging of intrinsic signals with 3-D reconstructions of neuronal circuitry.

Amblyopia↗
PubMedDate not supplied

The properties and possible mechanisms of interhemisphere synchronization in the motor cortex of the rat.

Cross-correlation analysis was used to observe interhemisphere synchronization of motor cortex neuron activity in anesthetized rats, which was seen on cross-correlograms as peaks located symmetrically relative to the coordinate origin. Peaks included "narrow" peaks (less than 20 msec) and "intermediate" peaks (30-80 msec). The results showed that the "common" source synchronizing the discharges of pairs of neurons located in different hemispheres of the brain might be a neuron (or group of neurons) located in one of the hemispheres and playing this role when there were reciprocal excitatory connections between it and each neuron in a pair. Comparison of the widths of symmetrical peaks with latent periods corresponding to transcallosal connections suggested that mono- and polysynaptic connections underlie the formation of "narrow" and "intermediate" peaks respectively.

Animals↗
PubMed1995

Time course of axonal myelination in the human brainstem auditory pathway.

Structures in the human brainstem auditory pathway, from the proximal end of the cochlear nerve to the inferior colliculus, undergo myelination between the 26th and 29th fetal weeks. By the 26th week of gestation, axons in the cochlear nerve and brainstem pathways have acquired linear arrays of oligodendrocytes, and faint myelin sheaths can be distinguished. By the 29th week, definitive myelination is present in all auditory pathways, including the proximal end of the cochlear nerve, trapezoid body, lateral lemniscus, dorsal commissure of the lemniscus, commissure of the inferior colliculus and brachium of the inferior colliculus. Subsequent to the 29th gestational week, density of myelination increases in all pathways until at least 1 year postnatal age. The time of onset of myelination coincides with the onset of acousticomotor reflexes and brainstem auditory evoked responses, processes which depend on rapid, synchronized conduction of auditory impulses in the cochlear nerve and brainstem. The cotemporality in appearance of myelin, reflex responses, and evoked responses supports the idea that the 26th to 28th gestational weeks are a critical period in the onset of human central auditory function. The subsequent increase in myelin density is likely to be a factor in the steady decrease in ABR wave III-V latencies observed during the perinatal period.

Axons↗