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PubMed1996

Odour encoding by temporal sequences of firing in oscillating neural assemblies.

Stimulus-evoked oscillatory synchronization of activity has been observed in many neural systems, including the cerebral cortex of mammals and the brain of insects. The possible functions of such rhythmic synchronization in neural coding, however, remain largely speculative. In the locust, odours evoke activity in dynamic (evolving) ensembles of transiently synchronized neurons. We report here that the active neurons composing these ensembles change in a stimulus-specific manner and with a high degree of reliability on a cycle-by-cycle basis during an odour response. Hence, information about an odour is contained not only in the neural assembly active at each oscillation cycle, but also in the precise temporal sequence in which these assemblies are updated during an odour response. Neural coding with oscillations thus allows combinatorial representations in time as well as in space.

Action Potentials↗
PubMed2006

Oscillations in the basal ganglia under normal conditions and in movement disorders.

A substantial body of work within the last decade has demonstrated that there is a variety of oscillatory phenomena that occur in the basal ganglia and in associated regions of the thalamus and cortex. Most of the earlier studies focused on recordings in rodents and primates. More recently, significant advances have been made in this field of research through the analysis of basal ganglia field potentials recorded from implanted deep brain stimulation electrodes in the basal ganglia of human patients with Parkinson's disease and other disorders. It now appears that oscillatory activity may play a significant role in the pathogenesis of these diseases. The most significant finding is that in Parkinson's disease synchronized oscillatory activity in the 10- to 35-Hz band (often termed "beta-band") is prevalent in the basal ganglia-thalamocortical circuits, and that such activity can be reduced by dopaminergic treatments. The entrainment of large portions of these circuits may disrupt information processing in them and may lead to parkinsonian akinesia (and perhaps tremor). Although less firmly established than the role of oscillations in movement disorders, oscillatory activities at higher frequencies may also be a component of normal basal ganglia physiology.

Animals↗
PubMed2006

Computational simulation of the input-output relationship in hippocampal pyramidal cells.

The precise mapping of how complex patterns of synaptic inputs are integrated into specific patterns of spiking output is an essential step in the characterization of the cellular basis of network dynamics and function. Relative to other principal neurons of the hippocampus, the electrophysiology of CA1 pyramidal cells has been extensively investigated. Yet, the precise input-output relationship is to date unknown even for this neuronal class. CA1 pyramidal neurons receive laminated excitatory inputs from three distinct pathways: recurrent CA1 collaterals on basal dendrites, CA3 Schaffer collaterals, mostly on oblique and proximal apical dendrites, and entorhinal perforant pathway on distal apical dendrites. We implemented detailed computer simulations of pyramidal cell electrophysiology based on three-dimensional anatomical reconstructions and compartmental models of available biophysical properties from the experimental literature. To investigate the effect of synaptic input on axosomatic firing, we stochastically distributed a realistic number of excitatory synapses in each of the three dendritic layers. We then recorded the spiking response to different stimulation patterns. For all dendritic layers, synchronous stimuli resulted in trains of spiking output and a linear relationship between input and output firing frequencies. In contrast, asynchronous stimuli evoked non-bursting spike patterns and the corresponding firing frequency input-output function was logarithmic. The regular/irregular nature of the input synaptic intervals was only reflected in the regularity of output inter-burst intervals in response to synchronous stimulation, and never affected firing frequency. Synaptic stimulations in the basal and proximal apical trees across individual neuronal morphologies yielded remarkably similar input-output relationships. Results were also robust with respect to the detailed distributions of dendritic and synaptic conductances within a plausible range constrained by experimental evidence. In contrast, the input-output relationship in response to distal apical stimuli showed dramatic differences from the other dendritic locations as well as among neurons, and was more sensible to the exact channel densities.

Action Potentials↗
PubMed1986

Neuronal activities in ventrobasal complex of thalamus and in trigeminal main sensory nucleus during EEG desynchronization in anesthetized rats.

Activities of somatosensory relay neurons responding to orofacial mechanical stimulation were examined in the ventrobasal complex of the thalamus (VB) and in the trigeminal main sensory nucleus (MSN) during EEG desynchronization in urethane-anesthetized rats. EEG desynchronization was induced by scrotal warming in a temperature range of 35-40 degrees C. Responses of most VB neurons to receptive-field stimulation were augmented during EEG desynchronization, when compared to responses during synchronization. Spontaneous activity of VB neurons also increased with EEG desynchronization. Responses of MSN neurons to receptive-field stimulation did not change appreciably when the EEG pattern was altered. If a VB neuron was induced by iontophoretic application of glutamate to fire at the same rate as seen during EEG desynchronization, a similar increased response to receptive-field stimuli was also observed. The augmented response of the VB neuron during desynchronization may thus have resulted from increased excitability of the neuron itself.

Animals↗
PubMed2002

Decreased neuronal synchronization during experimental seizures.

Synchronization between CA1 pyramidal neurons was studied using dual-cell patch-clamp techniques simultaneous with an extracellular measurement of network activity. We explored various linear and nonlinear methods to detect weak synchronization in this network, using cross-correlation, mutual information in one and two dimensions, and phase correlation in both broad and narrow band. The linear and nonlinear methods demonstrated different patterns of sensitivity to detect synchrony in this network, depending on the dynamical state of the network. Bursts in 4-amino-pyridine (4AP) were highly synchronous events. Unexpectedly, seizure-like events in 4AP were desynchronous events, both in comparison with interictal periods preceding the seizure without bursts (cut Schaffer collateral tract) and in comparison with bursts preceding the seizures (intact Schaffer collateral tract). The finding that seizure-like events are associated with desynchronization in such networks is consistent with recent theoretical work, suggesting that asynchrony is necessary to maintain a high level of activity in neuronal networks for sustained periods of time and that synchrony may disrupt such activity.

4-Aminopyridine↗
PubMed2006

Movement-related desynchronization-synchronization (ERD/ERS) in patients with Unverricht-Lundborg disease.

We studied changes in event-related desynchronization/synchronization (ERD/ERS) patterns in patients with Unverricht-Lundborg disease (ULD), presenting with prominent action myoclonus. We analyzed the movement-related ERD/ERS in alpha and beta frequency bands in 15 patients using self-paced finger extension as a motor paradigm and we compared the results with those obtained in 12 healthy volunteers. In all ULD patients, alpha- and beta-ERD regularly occurred with onset and location similar to that found in healthy controls, but the desynchronization of alpha activity was significantly greater than in controls (C3: -64.4+/-9.8% vs. -49.7+/-14.8%; p=0.004). Moreover, in the patients, both alpha- and beta-ERD spread toward frontal electrodes. In controls, the post-movement beta-ERS regularly occurred; it was absent in eight patients with severe action myoclonus, while, in seven patients with mild or moderate myoclonus, the beta-peak was significantly smaller with respect to that measured in controls (55.6+/-15.1% vs. 153.9+/-99.8%, p=0.006). The failure of beta-ERS well-correlated with motor impairment resulting from action myoclonus, whereas SSEPs and long-loop reflexes performed to detect signs of cortical hyperexcitability showed inconsistent changes. In ULD patients, ERD/ERS changes indicate an increased activation of motor cortex during movement planning and a great reduction of post-excitatory inhibition of motor cortex. The changes involving beta-ERS had a significant relationship with the functional disability in individual patients and might play a pathogenic role in the motor dysfunction.

Adult↗
PubMed2005

Synchronized firings in the networks of class 1 excitable neurons with excitatory and inhibitory connections and their dependences on the forms of interactions.

Synchronized firings in the networks of class 1 excitable neurons with excitatory and inhibitory connections are investigated, and their dependences on the forms of interactions are analyzed. As the forms of interactions, we treat the double exponential coupling and the interactions derived from it: pulse coupling, exponential coupling, and alpha coupling. It is found that the bifurcation structure of the networks depends mainly on the decay time of the synaptic interaction and the effect of the rise time is smaller than that of the decay time.

Action Potentials↗
PubMed1999

Gamma frequency-range abnormalities to auditory stimulation in schizophrenia.

BACKGROUND: Basic science studies at the neuronal systems level have indicated that gamma-range (30-50 Hz) neural synchronization may be a key mechanism of information processing in neural networks, reflecting integration of various features of an object. Furthermore, gamma-range synchronization is thought to depend on the glutamatergically mediated interplay between excitatory projection neurons and inhibitory neurons utilizing gamma-aminobutyric acid (GABA), which postmortem studies suggest may be abnormal in schizophrenia. We therefore tested whether auditory neural networks in patients with schizophrenia could support gamma-range synchronization. METHODS: Synchronization of the electroencephalogram (EEG) to different rates (20-40 Hz) of auditory stimulation was recorded from 15 patients with schizophrenia and 15 sex-, age-, and handedness-matched control subjects. The EEG power at each stimulation frequency was compared between groups. The time course of the phase relationship between each stimulus and EEG peak was also evaluated for gamma-range (40 Hz) stimulation. RESULTS: Schizophrenic patients showed reduced EEG power at 40 Hz, but not at lower frequencies of stimulation. In addition, schizophrenic patients showed delayed onset of phase synchronization and delayed desynchronization to the click train. CONCLUSIONS: These data provide new information on selective deficits in early-stage sensory processing in schizophrenia, a failure to support the entrainment of intrinsic gamma-frequency oscillators. The reduced EEG power at 40 Hz in schizophrenic patients may reflect a dysfunction of the recurrent inhibitory drive on auditory neural networks.

Acoustic Stimulation↗
PubMed1984

Hippocampal electrical activity and behavior in the presence of novel environmental stimuli in rabbits.

Male rabbits have been used in a simultaneous study of their behavioral and neural activity in different experimental situations related to attention and emotionality. The electrical activity of the dorsal hippocampus and frontal cortex was recorded in the following experimental situations: Neutral Environment (response to a novel environment); Object (response to a novel stimulus); Stuffed sparrow hawk; and live cat. Results show that behavioral and electrical responses depend upon: (a) the nature of the stimulus; and (b) whether or not the stimulus is moving. As for the immobile stimuli, the stuffed animal presentation significantly reduced both behavioral activity and percentage and frequency of rhythmic slow activity (RSA); prolonged periods of ECoG synchronization were also recorded. The introduction of the live cat greatly increased the percentage and frequency of RSA, especially when the cat was looking at the rabbit. The experimental situations caused differences in the distribution of RSA frequencies as well. The percentage of high RSA frequencies (greater than 6.5 Hz during immobility; greater than 7.2 Hz during movement) recorded in response to the immobile stimuli was negatively correlated to the amount of RSA. Results are discussed in the light of attentional and emotional theories.

Animals↗
PubMed1999

Event-related EEG/MEG synchronization and desynchronization: basic principles.

An internally or externally paced event results not only in the generation of an event-related potential (ERP) but also in a change in the ongoing EEG/MEG in form of an event-related desynchronization (ERD) or event-related synchronization (ERS). The ERP on the one side and the ERD/ERS on the other side are different responses of neuronal structures in the brain. While the former is phase-locked, the latter is not phase-locked to the event. The most important difference between both phenomena is that the ERD/ERS is highly frequency band-specific, whereby either the same or different locations on the scalp can display ERD and ERS simultaneously. Quantification of ERD/ERS in time and space is demonstrated on data from a number of movement experiments.

Cortical Synchronization↗
PubMedDate not supplied

[Interaction foci, informational synthesis and mental processes].

Brain organization of mental activity is based on the nervous integration, specialization of functions and combination of rigid and flexible connections. First of them are provided by structural changes in synapses, the second--by a coincidence of rhythmic characteristics and synchronization of the activity. These principles are realized in dynamic structures--interaction foci, revealed in the cortex during the process of mental activity by a method of mapping the intracortical interaction. Interaction foci are the centers of nervous connections. Each group has its appropriate frequency characteristics and is connected with the isorhythmic nervous elements at the periphery. Construction of the interaction focus provides the synthesis of the information coming from the sensory organs and the centers of motivations and that extracted from the memory. Informational synthesis is in the basis of the mental functions, having a rigid nucleus and a system of peripheral connections whose configuration can be changed, stipulating a unique character of experienced psychic feeling. Topography of interaction foci is different at different mental acts, realizing a principle of functional specialization. At perception the projection cortex is the center of integration, at thinking that are the cortical associative zones. Imaginable thinking is predominantly connected with the parieto-temporal, abstract--with the frontal cortical areas. Probably two basic functions of consciousness--integration of the "Self" including voluntary factor and communication-are also separated in space.(ABSTRACT TRUNCATED AT 250 WORDS)

Brain↗
PubMed2005

How the brain blinks: towards a neurocognitive model of the attentional blink.

When people monitor a visual stream of rapidly presented stimuli for two targets (T1 and T2), they often miss T2 if it falls into a time window of about half a second after T1 onset-the attentional blink (AB). We provide an overview of recent neuroscientific studies devoted to analyze the neural processes underlying the AB and their temporal dynamics. The available evidence points to an attentional network involving temporal, right-parietal and frontal cortex, and suggests that the components of this neural network interact by means of synchronization and stimulus-induced desynchronization in the beta frequency range. We set up a neurocognitive scenario describing how the AB might emerge and why it depends on the presence of masks and the other event(s) the targets are embedded in. The scenario supports the idea that the AB arises from "biased competition", with the top-down bias being generated by parietal-frontal interactions and the competition taking place between stimulus codes in temporal cortex.

Attention↗
PubMed2006

Imitating versus non-imitating movements: differences in frontal electroencephalographic oscillatory activity.

Non phase-locked oscillatory changes were studied in seven healthy volunteers during two different reaction time movement paradigms, in which the stimulus was a wrist movement (either extension or flexion) performed by another person seated in front of the subject (examiner). In the first paradigm (imitation), the subject was instructed to perform the same movement observed. In the second paradigm (non-imitation), the subject was instructed to perform the opposite movement (flexion when an extension was observed, and vice-versa). Changes in the 7-37 Hz range band were determined by means of Gabor transforms. A frontal energy increase (event-related synchronization, ERS) around 15 Hz could be observed in the frontal region after the examiner's movement; this frontal ERS was significantly larger in the non-imitation paradigm. A typical alpha and beta movement-related event-related desynchronization/synchronization (ERD/ERS) pattern was also observed in both paradigms in the central region. The beta-ERD was significantly larger in the imitation paradigm. Our results show that the motor preparation mechanisms involved in an imitated and a non-imitated movement are different.

Adult↗
PubMed2005

Attention modulates hemispheric differences in functional connectivity: evidence from MEG recordings.

The present study examined intrahemispheric functional connectivity during rest and dichotic listening in 8 male and 9 female healthy young adults measured with magnetoencephalography (MEG). Generalized synchronization within the separate hemispheres was estimated by means of the synchronization likelihood that is sensitive to linear as well as non-linear coupling of MEG signals. We found higher functional intrahemispheric connectivity of frontal and temporal areas within the right as compared to the left hemisphere in the lower and higher theta band during rest and in the lower theta band during dichotic listening. In addition, higher synchronization in the lower theta band correlated with better task performance. In the upper alpha band, hemispheric differences in intrahemispheric connectivity of the frontal regions were found to be modulated by focused attention instructions. That is, attention to the right ear exaggerates the pattern of higher synchronization likelihood for the right frontal region, while attention to the left ear has an opposite effect. We found higher intrahemispheric connectivity in males compared to females as shown by higher synchronization in the lower alpha band. Taken together, our results reflect a physiological basis for functional hemispheric laterality and support the general assumption of sex differences in brain organization. Furthermore, in addition to studies that show that controlled attention processes modulate activation of the frontal areas, our study indicates that attention modulates ipsilateral functional connectivity in the frontal areas. This supports the idea of a supervisory role for the frontal cortex in attention processes.

Acoustic Stimulation↗
PubMed2003

Spatiotemporal patterns of beta desynchronization and gamma synchronization in corticographic data during self-paced movement.

OBJECTIVE: To study the spatiotemporal pattern of event-related desynchronization (ERD) and event-related synchronization (ERS) in electrocorticographic (ECoG) data with closely spaced electrodes. METHODS: Four patients with epilepsy performed self-paced hand movements. The ERD/ERS was quantified and displayed in the form of time-frequency maps. RESULTS: In all subjects, a significant beta ERD with embedded gamma ERS was found. CONCLUSIONS: Self-paced movement is accompanied not only by a relatively widespread mu and beta ERD, but also by a more focused gamma ERS in the 60-90 Hz frequency band.

Adult↗
PubMed2005

Modulations in the degree of synchronization during ongoing oscillatory activity in the human brain.

When a subject is asked to respond as quickly as possible to a stimulus he/she responds much faster if this stimulus is preceded by a warning cue. This cue enables the subject to anticipate the forthcoming stimulus, initiating neural processes subserving the future perception and processing of the target stimulus and the motor preparation of the associated response action. It has recently been suggested that neuronal activity before such an anticipated target stimulus could be associated with modulations in neuronal synchronization and oscillatory activity. Here we recorded electrical brain activity whilst subjects performed a choice reaction time task, in which one of the stimuli could be predicted with 90% certainty. We show that the prediction of a forthcoming stimulus was associated with an increase in gamma oscillations overlying occipital areas and a decrease in beta oscillations overlying sensorimotor cortex before the stimulus was presented. We suggest that these regionally specific modulations in oscillatory activity reflect the establishment of neural networks that are 'primed' for the future processing of the forthcoming predictable visual stimulus.

Adult↗
PubMed2006

Cognition- and memory-related ERD/ERS responses in the auditory stimulus modality.

In the year 1994, Krause et al. published an initial report of acoustically elicited electroencephalogram (EEG) event-related desynchronization (ERD)/ event-related synchronization (ERS) responses. Later, Krause et al. reported of distinct ERD/ERS responses during an auditory memory task: the encoding of acoustic material elicited alpha-frequency ERS whereas retrieval or recognition of the same stimulus material evoked alpha ERD. The research group of Krause and co-workers has published several reports on acoustically evoked ERD/ERS responses utilizing various cognitive tasks and diverse stimuli. Recently, also clinical studies have been initiated. This chapter reviews, summarizes, and discusses the findings on cognition- and memory-related ERD/ERS responses specifically in the auditory stimulus modality.

Acoustic Stimulation↗
PubMedDate not supplied

[Analysis of changes in the electrical activity of the neocortex in dogs during the formation of the stereotype of food-procuring conditioned reflexes in them].

A system of food-procuring conditioned reflexes (dynamic stereotype after I.P. Pavlov) was elaborated in dogs. In the interstimuli periods, 0.6 to 0.8 sec. prior the action of the conditioned stimulus, they exhibited a "state of expectancy" characterized by an increase of frequency (up to 80 per sec.) of potential oscillations of a small amplitude (20 to 30 mcv) and their pronounced sychroneity, predominantly in the anterior parts of the neocortex. The conditioned signal acting against such background produced specific reactions in the form of a limited number of bursts (3 to 4 in 0.5 sec.) of highfrequency (up to 100 per sec.) synchronized activity (HSA) of considerable amplitude (50 to 60 mcv) which always preceded conditioned reactions, being in certain temporal relations with them. A correlation-spectral analysis has shown that in the HSA period, electrical activity became considerably more regular; in the intensity spectra the extreme frequencies of the analyzed band (5 to 7 c/s and 90 to 100 c/s) became prominent, and in most cases high values of the coherence function were due to them. HSA reactions are regarded as a major link in the trigger mechanism of conditioned food-procuring reactions.

Animals↗