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PubMed2005

Reduced gamma-band coherence to distorted feedback during speech when what you say is not what you hear.

BACKGROUND: Communication between the frontal lobes, where speech is generated, and the temporal lobes, where it is perceived, may occur through the action of an efference copy/corollary discharge mechanism that prepares the temporal lobes for the expected sound. We suggest that coherence of EEG in gamma-band between frontal and temporal lobes may reflect the successful action of such a mechanism. We tested the hypothesis that there would be a disruption of gamma-band coherence when the expected auditory consequence of speech does not match the auditory experience. METHOD: EEG was recorded from 21 healthy adult subjects as they uttered the sound [a:] (Talking condition) and as they heard these recorded sounds played back (Listening condition). As they spoke, subjects heard real-time feedback of the sounds that were: (1) pitch-shifted down one semi-tone, (2) pitch-shifted down one-half of a semi-tone, or (3) not pitch-shifted (veridical), each in separate runs. Event-related gamma coherence between frontal and temporal sites was calculated relative to the onset of the sound, as it was being spoken during Talking, and as it was being played back during Listening. RESULTS: Frontal-temporal gamma-band coherence spanning 33-43 Hz was greater during Talking than Listening and greater when speech was veridical than when it was distorted a whole semi-tone. CONCLUSIONS: Gamma-band fronto-temporal synchrony may reflect a "binding of expectation with experience." Disruption of this synchrony may provide feedback to the frontal lobes, particularly regions subserving vocalization, to implement sensorimotor adaptations to either adjust motor programs for speech production in the short run, or to reorganize expectations in the long run.

Adult↗
PubMed2005

EEG coherence.

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Brain↗
PubMed2006

The theory of the whole-brain-work.

The theory of the whole-brain-work basically explains the oscillatory dynamics of the human and nonhuman brain during cognitive processing. The theory is based on principles according to which brain functions are represented by the oscillatory activity. Oscillatory activity in a given frequency band performs multiple functions since they vary on a number of response parameters. There is selective cooperation in the stimulated brain; this produces super-binding between neural populations and super-synergy in the whole brain. The concept of super-synergy thus includes super-binding and, additionally, entropy and the role of EEG-oscillations as control parameters in brain's responsiveness. In super-synergy, spatial integration occurs through the selective cooperation of brain structures. Temporal integration occurs in line with the principle of superposition of oscillations in which the comparative polarity and phase angle are critical for forming the function-specific configurations. Extension of the theory of whole-brain-work to cognitive processing proposes that there is a constant reciprocal activation within the subprocesses of attention, perception learning and remembering and this leads to an APLR-alliance. In such a context, all brain functions are inseparable, for instance, from memory function and, in turn, memory states have no exact boundaries along the time space; memory states thus evolve in the APLR-alliance. The theory claims that the reentry and the dynamic behavior of oscillations during the reciprocal activation in APLR-alliance are among the causal factors for brain dynamics and for cognition.

Animals↗
PubMed2006

Theory of the normal waking EEG: from single neurones to waveforms in the alpha, beta and gamma frequency ranges.

The classic alpha rhythm, recorded intracortically, consists of alternating surface-negative troughs and briefer surface-positive peaks. The troughs are associated with neuronal hyperpolarization, the peaks with brief depolarization and burst firing. Each hyperpolarization is mainly a potassium potential, lasting approximately 100 ms. Depolarization and burst firing arise when this inactivates. In the desynchronized state, membrane potential is poised just below threshold. Firing in vivo is somewhat irregular and non-bursting. It is suggested that EEG bistability (classic alpha vs desynchronization) corresponds to bistability of single pyramidal cells. In vitro, paired pulses lead to depression of synaptic transmission in synapses linking two pyramidal cells, but to facilitation in synapses linking pyramidal cells to inhibitory neurones. These effects should be recruited by burst firing in vivo. Thus, enhancement of inhibitory and excitatory transmission occur respectively during the classic alpha rhythm, and the desynchronized state. As a result both states tend to be self-sustaining. In the desynchronized state high frequency (gamma or beta) activity predominates. In simulations, gamma activity has been modeled as the behaviour of cortical networks where populations of excitatory and inhibitory neurones interact. These simulations assume conduction times between neurones to be negligible. However, this is not true for long-distance interactions. Introduction into the models of plausible conduction delays should slow the oscillation frequency. The activated cortex can then produce not only gamma activity but also beta, and sometimes alpha activity. Thus, alpha frequencies can arise both in the "idling" cortex (classic alpha), and in the activated cortex, although the respective mechanisms are quite different.

Alpha Rhythm↗
PubMed2006

Therapeutic modulation of synaptic connectivity with desynchronizing brain stimulation.

In a modeling study, we show that synaptic connectivity can effectively be reshaped by an appropriate modulation of neuronal dynamics. To this end, we incorporate synaptic plasticity with symmetric spike-timing characteristics into a population of bursting neurons, which are interacting via chemical synapses. Under spontaneous conditions, qualitatively different stable dynamical states may coexist. We observe states characterized either by pathological synchrony or by uncorrelated activity. Suitably designed stimulation protocols enable to shift the neuronal population from one dynamical state to another. Due to low-frequency periodic pulse train stimulation, the population learns pathologically strong interactions, as known from the kindling phenomenon. In contrast, desynchronizing stimulation, e.g., multi-site coordinated reset stimulation, enables the network to unlearn pathologically strong synaptic interactions, so that a powerful long-term anti-kindling is achieved. We demonstrate that anti-kindling can be achieved even with weak and/or short desynchronizing stimuli, which are not able to cause a complete desynchronization in the course of the stimulation. Our results show that desynchronizing stimulation may serve as a novel curative approach for the therapy of neurological diseases connected with pathological cerebral synchrony.

Algorithms↗
PubMed2007

Trait affect moderates cortical activation in response to state affect.

To examine the influence of trait affect on cortical activation during state affect, 32 healthy female participants viewed video clips to induce positive and negative emotional states. Frontal and parietal electroencephalogram (EEG) of the alpha band was assessed while participants imagined the scene of each video that generated the most intense emotions. The results showed that affect-induced frontal asymmetry was moderated by negative trait affect. The difference in frontal asymmetry between positive and negative state affect increased linearly with negative trait affect. Moreover, positive trait affect was negatively correlated with activation in the right-parietal brain region. These results suggest that trait affect moderates the effects of state affect on brain activation.

Adolescent↗
PubMed2006

A coherence-based technique for separating phase-locked from non-phase-locked power spectrum estimates during intermittent stimulation.

In addition to evoked responses, which are phase-locked to the stimuli, the stimulation may also change the ongoing EEG in a time-locked manner. This change has been investigated in event-related synchronization/desynchronization (ERS/ERD) studies by comparing the spectra before and during stimulation or alternatively by using the intertrial variance method (IVM). In the present work, a technique based on the coherence estimate (kappa(y)(2)(f)) between the stimulation signal and the EEG is proposed for separating the ongoing EEG activity spectrum from that of the evoked responses. Furthermore, a statistical criterion is applied to reduce spurious spectral peaks. The performance of this procedure was assessed through simulation and illustrated with EEG during photic stimulation. For simulated data (signal-to-noise-ratio of 0.995 within 10-12.5 Hz) kappa(y)(2)(f) led to a non-phase-locked spectrum estimate with an average normalized error of 12.4%, which is reduced to only 0.2% after applying the statistical criterion. The methodology proposed is asymptotically equivalent to the IVM but it does not require previous filtering the EEG data. Kappa(y)(2)(f) together with the statistical correction criterion allows investigating the entrainment within a narrow-band range, particularly in frequencies close to that of the alpha peak. Hence it is useful in ERS/ERD studies. Moreover, it can be also used for characterizing frequencies within the gamma band.

Adult↗
PubMed2006

Estimation of short-time cross-correlation between frequency bands of event related EEG.

Simultaneous variations of the event-related power changes (ERD/ERS) are often observed in a number of frequency bands. ERD/ERS measures are usually based on the relative changes of power in a given single frequency band. Within such an approach one cannot answer questions concerning the mutual relations between the band-power variations observed in different frequency bands. This paper addresses the problem of estimating and assessing the significance of the average cross-correlation between ERD/ERS phenomena occurring in two frequency bands. The cross-correlation function in a natural way also provides estimation of the delay between ERD/ERS in those bands. The proposed method is based on estimating the short-time cross-correlation function between relative changes of power in two selected frequency bands. The cross-correlation function is estimated in each trial separately and then averaged across trials. The significance of those mean cross-correlation functions is evaluated by means of a nonparametric test. The basic properties of the method are presented on simulated signals, and an example application to real EEG and ECoG signals is given.

Adult↗
PubMed2003

Effect of L-Dopa on the pattern of movement-related (de)synchronisation in advanced Parkinson's disease.

In the early stages of Parkinson's disease (PD), impaired motor preparation has been related to a delay of mu rhythm movement-related desynchronisation, suggesting hypoactivation of the contralateral, primary sensorimotor (PSM) cortex. Following movement, a decrease in the amplitude of beta rhythm movement-related synchronisation was observed over the same region. This decrease--not seen in control subjects--was thus thought to be related to an impairment in cortical deactivation. By monitoring movement-related (de)synchronisation, we aimed (i) to extend to advanced PD the observations made in less-advanced situations and (ii) to test the effect of acute L-Dopa on these abnormalities. The United Parkinson's Disease Rating Scale (UPDRS) III score decreased by about 60% following acute L-Dopa administration, and we observed the following concurrent changes: a marked increase in mu desynchronisation pre-movement latency (thus reduced delay) during movement preparation over contralateral, central regions; an increase in mu desynchronisation during movement execution over bilateral central regions; a decrease in mu desynchronisation latency over bilateral frontocentral regions, and a significant increase in beta synchronisation over contralateral, central regions after movement. Changes of mu and beta rhythm parameters seemed to be inversely correlated with bradykinesia. Mu rhythm desynchronisation latency and beta synchronisation amplitude further decreased in advanced PD compared to earlier stages of the disease, suggesting greater impairment of cortical activation/deactivation as the disease progresses. L-Dopa partially restored the abnormal mu and beta rhythm cortical (de)synchronisation patterns over the PSM cortex.

Adult↗
PubMed2003

Sensitivity of human EEG alpha band desynchronization to different working memory components and increasing levels of memory load.

Event-related alpha band desynchronization is frequently used to analyze spatiotemporal cortical activation patterns during the performance of cognitive tasks. In the present paper the sensitivity of alpha band desynchronization to increasing levels of cognitive load and to different cognitive working memory components is investigated. A 27-channel electroencephalogram of 62 participants while solving (a) a short-term memory and (b) a working memory task (dual task), each with five levels of memory load, was analyzed. We found (a) a linearly increasing desynchronization in the upper alpha band with ascending cognitive load, and (b) evidence of the involvement of distinguishable cognitive components (storage and controlled attention) in the memory tasks.

Alpha Rhythm↗
PubMed2004

EEG power and coherence analysis of visually presented nouns and verbs reveals left frontal processing differences.

Spectral power and coherence of the electroencephalogram was measured while subjects read either a verb or a noun which initiated a short meaningful phrase. For both types of words theta-power decreased substantially relative to a prestimulus baseline at left anterior electrode sites. All other frequency bands showed less (alpha, beta) or no effects at all (gamma). The theta-power attenuation was more pronounced for verbs than for nouns, thus indicating a stronger desynchronization for verbs at left frontal sites. Coherence of the theta-band revealed that these left anterior electrodes became decoupled from left and right posterior sites, again more for verbs than for nouns. These spectral changes are assumed to reflect processing differences due to the grammatical status of the two word categories.

Adult↗
PubMed2004

Gender differences in hemispheric organization during divergent thinking: an EEG investigation in human subjects.

This study examined the gender-related differences in EEG patterns during the experimental condition of divergent thinking. The EEG of 36 males and 27 females was recorded from 16 scalp electrodes in rest and while students were solving a creative problem. The spectral power density along with EEG coherence estimates were analyzed in each of the six frequency bands in the 4-30 Hz range. Gender-related differences in the EEG patterns were found during successful divergent thinking. Creative men were characterized by massive increases of amplitude and interhemispheric coherence in the beta2 whereas creative women showed more local increases of the beta2 power and coherence. On the contrary, the task-induced desynchronization of the alpha1 rhythm in creative women was topographically more expanded as compared with men who demonstrated greater interhemispheric coherence than women did. Our results propose a different hemispheric organization in men and women during creative thinking.

Alpha Rhythm↗
PubMed2004

Impairment of a cortical event-related desynchronisation during a bimanual load-lifting task in children with autistic disorder.

In autism, the abilities of communication are affected, associated with abnormalities of cognitive, sensorial and motor development. In a previous study based on a load-lifting task, we showed impairment of anticipation in children with autism as evidenced by kinematics and eletromyographic recordings [Neurosci. Lett. 348 (2003) 17]. In the present study, we assessed the cortical counterparts of the use of anticipatory postural adjustments in a group of control children and in a group of children with autism. The tasks required maintaining a stable forearm position despite imposed or voluntary lifting of an object placed either on the controlateral forearm or on a support. We investigated the differences between the two groups of children on the Event-Related Desynchronisation (ERD) which precedes movement onset in adults [Electroencephalogr. Clin. Neurophysiol. 46 (1979) 138]. Electroencephalogram (EEG) power evolution of a 6-8-Hz frequency band was averaged before and after imposed or voluntary movement onset. EEG reactivity of control and autistic children did not differ during the imposed unloading condition, but significant differences appeared in the voluntary unloading situations. Before lifting the object, control children showed an ERD above the left motor areas. An ERD also occurred above the right motor areas when the object was placed on their forearm. This indicates that the ERD can also translate the use of anticipatory postural adjustments. By contrast, children with autism did not show an ERD in the two voluntary situations. This suggests a central deficit of anticipation in both postural and motor control in children with autism.

Autistic Disorder↗
PubMed2005

Beta rebound after different types of motor imagery in man.

We investigated the behavior of short-lasting beta bursts (beta rebound, beta ERS) induced after imagination of hand, foot or tongue movement. Nine able-bodied subjects were asked to imagine one type of movement following the presentation of a visual cue stimulus. EEG was recorded from 60 closely spaced electrodes placed over frontal, central and parietal areas. Spatiotemporal ERD/ERS patterns were evaluated in form of time-frequency maps. Seven out of nine subjects displayed a significant short-lasting beta power increase (beta rebound) after termination of imagery of movement of both feet in the frequency range of 23-29Hz with a clear maximum at the vertex. In contrast, only two subjects displayed a clear beta rebound at the vertex after imagery of one of the hands, although five exhibited a significant beta rebound at the contralateral side of the head. None showed a beta rebound after tongue motor imagery. The midcentrally located beta rebound is interpreted as an electrophysiological correlate of a simultaneous "resetting" of overlapping neural networks in the foot representation areas and the SMA.

Adult↗
PubMed2005

Intelligence related differences in EEG-bandpower.

Several studies on the relationship between event-related desynchronization/synchronization (ERD/ERS) and cognitive performance revealed contradictory results particularly for the alpha band. Studies from our laboratory have shown that good performers show a larger upper alpha ERD (interpreted in terms of larger cortical activation) than bad performers. In contrast, other researchers found evidence for the neural efficiency hypothesis, which states that more intelligent subjects exhibit a smaller extent of cortical activation, which is assumed to be reflected by a smaller upper alpha ERD. Here we address the question whether these divergent results may be due to differences in general task difficulty. Using a modified version of the RAVEN, individually divided into easy and difficult tasks, a group of average and a group of highly intelligent subjects (IQ- and IQ+) have been investigated. While in the theta frequency IQ+ subjects generally exhibited a significantly stronger activation, we found a significant interaction of task difficulty and IQ group in the upper alpha band, indicating both, a weaker activation for the high IQ group during the easy tasks, and a significant increase from easy to difficult tasks for IQ+ only.

Adolescent↗
PubMed2005

The effect of isoflurane and halothane on electroencephalographic activation elicited by repetitive noxious c-fiber stimulation.

Windup is the progressive increase in neuronal response to a repetitive noxious stimulus. This response is most often observed in the spinal cord, but it is unclear how this response is manifested in supraspinal structures. We investigated the effects of isoflurane and halothane on electroencephalographic responses to repetitive noxious electrical stimuli (20 pulses at 0.1, 1 and 3 Hz) applied to the tail in rats. Halothane and isoflurane concentrations were adjusted to 0.8 and 1.2 minimum alveolar concentration (MAC), where MAC is the concentration needed to prevent gross and purposeful movement in 50% of animals. At 0.8 MAC halothane, the 3 Hz stimulus caused electroencephalographic (EEG) activation primarily by increasing the median edge frequency (MEF), while at 1.2 MAC halothane the spectral edge frequency (SEF) was increased by the 1 and 3 Hz stimuli, and the MEF was increased by the 3 Hz stimuli. At 0.8 MAC isoflurane, the 1 and 3 Hz stimuli evoked EEG activation by increasing the MEF and SEF, while at 1.2 MAC only the MEF was increased by the 1 Hz stimulus. No EEG activation occurred with the 0.1 Hz repetitive stimulus with either isoflurane or halothane. These data suggest that repetitive electrical stimulation normally associated with windup in spinal neurons can evoke EEG activation.

Anesthetics, Inhalation↗
PubMed2005

Volatile anesthetics disrupt frontal-posterior recurrent information transfer at gamma frequencies in rat.

We seek to understand neural correlates of anesthetic-induced unconsciousness. We hypothesize that cortical integration of sensory information may underlie conscious perception and may be disrupted by anesthetics. A critical role in frontal-posterior interactions has been proposed, and gamma (20-60 Hz) oscillations have also been assigned an essential role in consciousness. Here we investigated whether general anesthetics may interfere with the exchange of information encoded in gamma oscillations between frontal and posterior cortices. Bipolar electrodes for recording of event-related potentials (ERP) were chronically implanted in the primary visual cortex, parietal association and frontal association cortices of six rats. Sixty light flashes were presented every 5s, and ERPs were recorded at increasing concentrations of halothane or isoflurane (0-2%). Information exchange was estimated by transfer entropy, a novel measure of directional information transfer. Transfer entropy was calculated from 1-s wavelet-transformed ERPs. We found that (1) feedforward transfer entropy (FF-TE) and feedback transfer entropy (FB-TE) were balanced in conscious-sedated state; (2) anesthetics at concentrations producing unconsciousness augmented both FF-TE and FB-TE at 30 Hz but reduced them at 50 Hz; (3) reduction at 50 Hz was more pronounced for FB-TE, especially between frontal and posterior regions; (4) at high concentrations, both FF-TE and FB-TE at all frequencies were at or below conscious-sedated baseline. Our findings suggest that inhalational anesthetics preferentially impair frontal-posterior FB information transfer at high gamma frequencies consistent with the postulated role of frontal-posterior interactions in consciousness.

Anesthetics, Inhalation↗
PubMed2006

Long-term enhanced desynchronization of the alpha rhythm following tetanic stimulation of human visual cortex.

It had been shown previously that a photic tetanus induces LTP-like changes in the visual cortex, as indexed by an enhancement of the N1b component of the visual evoked potential, recorded non-invasively by electroencephalography. This potentiation was shown to last over 1 h. In the present study, the effect of a photic tetanus on oscillatory activity is investigated. EEGs were collected from eight healthy subjects in three conditions while visual checkerboards were displayed. Following baseline presentations in two conditions a lateralized visual tetanus was given, either to the left or right visual field, and in a third condition no tetanus was given. This was followed by a return to baseline presentations, both immediately after the tetanus/control block, and 1 h later. Enhanced event-related desynchronization (ERD) of the alpha rhythm lasting 1 h was seen following the photic tetanus over occipital electrodes. Because ERD of the alpha rhythm is thought to represent active cortex, these results suggest that the visual tetanus induces long-lasting cortical changes, with stronger neuronal assemblies and increased neuronal output.

Adult↗