Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Cortical Synchronization”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,207 records · Page 67Linked to original sources
PubMed1996

"One-way asynchrony' of burst-suppression activity.

In a patient with traumatic intracerebral lesions, we recorded two subsequent electroencephalograms with burst-suppression activity. Between the two measurements, the clinical condition of the patient deteriorated. The first EEG showed symmetrical interhemispheric asynchrony of bursts. In the second EEG, however, we noted synchrony from one hemisphere to the other, but asynchrony in the opposite direction. We propose a simple model that can explain why one-way asynchrony of burst-suppression activity is prognostically more severe than symmetrical asynchrony.

Adult↗
PubMed1999

[Event-related desynchronization and Parkinson disease. Importance in the analysis of the phase of preparation for movement].

This study was aimed at determining the spatiotemporal distribution of event-related desynchronization (ERD) during self-paced voluntary movement in order to establish the interest of this method for the analysis of movement programming in Parkinson's disease. Desynchronization of mu rhythm was recorded 2 s before to 0.5 s after right then left self-paced voluntary wrist flexions from 11 leads covering the primary sensorimotor cortex (central), supplementary motor area (frontocentral) and parietal cortex (parietocentral). Recordings were obtained from ten control subjects, ten patients treated for Parkinson's disease (bilateral symptoms) and 20 patients presenting with right or left hemiparkinsonism before and after chronic administration of L-dopa. In the control group, ERD started over the contralateral primary sensorimotor cortex 1,750 ms before movement and was bilateral just before performance of the movement. In both treated and de novo Parkinson's disease groups, decrease in ERD latency (1,000 to 1,250 ms before movement) was only observed when movements were performed with the akinetic hand and corresponded to a decrease in motor cortical activity. This confirmed that programming of movement is affected in Parkinson's disease. Earlier ERD with central ipsilateral distribution were also observed, suggesting that other cortical areas might be activated to compensate for dysfunction of movement programming and to increase the level of cortical activity required for performance of the movement. The administration of L-dopa to de novo hemiparkinsonians patients resulted in increased ERD latency over contralateral and ipsilateral central areas. As in the treated Parkinson's disease group, frontocentral ERD could also be recorded. L-dopa would thus partially restore the affected motor programmation and modulate cortical activation in both supplementary motor area and primary motor cortex, the later receiving more afferences from basal ganglia.

Antiparkinson Agents↗
PubMed2003

Differential effects of low-frequency rTMS at the occipital pole on visual-induced alpha desynchronization and visual-evoked potentials.

Visual-induced alpha desynchronization (VID) and visual-evoked potentials (VEPs) characterize occipital activation in response to visual stimulation but their exact relationship is unclear. Here, we tested the hypothesis that VID and VEPs reflect different aspects of cortical activation. For this purpose, we determined whether VID and VEPs are differentially modulated by low-frequency repetitive transcranial magnetic stimulation (rTMS) over the occipital pole. Scalp EEG responses to visual stimuli (flashed either to the left or to the right visual field) were recorded for 8 min in six healthy subjects (1) before, (2) immediately following, and (3) 20 min after left occipital rTMS (1 Hz, 10 min). The parameters aimed to reduce cortical excitability beyond the end of the TMS train. In addition, simple reaction times to visual stimulation were recorded (left or right hand in separate blocks). In all subjects, VID was significantly and prominently reduced by rTMS (P = 0.0001). In contrast, rTMS failed to modulate early VEP components (P1/N1). A moderate effect was found on a late VEP component close to manual response onset (P = 0.014) but this effect was in the opposite direction to the VID change. All changes were restricted to the targeted left occipital cortex. The effects were present only after right visual field stimulation when a right hand response was required, were associated with a behavioral effect, and had washed out 20 min after rTMS. We conclude that VID and early VEPs represent different aspects of cortical activation. The findings that rTMS did not change early VEPs and selectively affected VID and late VEPs in conditions where the visual input must be transferred intrahemispherically for visuomotor integration (right visual field/right hand) are suggestive of rTMS interference with higher-order visual functions beyond visual input. This is consistent with the idea that alpha desynchronization serves an integrative role through a corticocortical "gating function."

Adult↗
PubMed2003

Group imaging of task-related changes in cortical synchronisation using nonparametric permutation testing.

Synthetic aperture magnetometry (SAM) is a nonlinear beamformer technique for producing 3D images of cortical activity from magnetoencephalography data. We have previously shown how SAM images can be spatially normalised and averaged to form a group image. In this paper we show how nonparametric permutation methods can be used to make robust statistical inference about group SAM data. Data from a biological motion direction discrimination experiment were analysed using both a nonparametric analysis toolbox (SnPM) and a conventional parametric approach utilising Gaussian field theory. In data from a group of six subjects, we were able to show robust group activation at the P < 0.05 (corrected) level using the nonparametric methods, while no significant clusters were found using the conventional parametric approach. Activation was found using SnPM in several regions of right occipital-temporal cortex, including the superior temporal sulcus, V5/MT, the fusiform gyrus, and the lateral occipital complex.

Adult↗
PubMed2003

Structural (operational) synchrony of EEG alpha activity during an auditory memory task.

Memory paradigms are often used in psycho-physiological experiments in order to understand the neural basis underlying cognitive processes. One of the fundamental problems encountered in memory research is how specific and complementary cortical structures interact with each other during episodic encoding and retrieval. A key aspect of the research described below was estimating the coupling of rapid transition processes (in terms of EEG description) which occur in separate cortical areas rather than estimating the routine phase-frequency synchrony in terms of correlation and coherency. It is assumed that these rapid transition processes in the EEG amplitude correspond to the "switching on/off" of brain elemental operations. By making a quantitative estimate of the EEG structural synchrony of alpha-band power between different EEG channels, it was shown that short-term memory has the emergent property of a multiregional neuronal network, and is not the product of strictly hierarchical processing based on convergence through association regions. Moreover, it was demonstrated that the dynamic temporal structure of alpha activity is strongly correlated to the dynamic structure of working memory.

Acoustic Stimulation↗
PubMed2000

Functional dissociation of lower and upper frequency mu rhythms in relation to voluntary limb movement.

OBJECTIVE: The goal of this study is to investigate the reactivity of central rhythms in the alpha band during self-paced voluntary finger and foot movement and to give an answer to the question, whether different types of mu rhythms exist. METHODS: The effect of self-paced, voluntary finger and foot movement was studied in a group of 12 right-handed healthy volunteers. The EEG was recorded from a grid of 34 electrodes placed over sensorimotor areas with inter-electrode distances of approximately 2.5 cm. The event-related desynchronization (ERD) was quantified in the 8-10 and 10-12 Hz bands. RESULTS: Both frequency components are blocked prior to and during movement and therefore, they have to be considered as mu rhythms. The lower frequency component results in a widespread movement-type non-specific ERD pattern, whereas the upper frequency component shows a more focused and movement-type specific pattern, clearly different with finger and foot movement. CONCLUSIONS: The distinct reactivity patterns provide evidence for the existence of two types of mu rhythms, a somatotopically non-specific lower frequency mu rhythm and a somatotopically specific mu rhythm characteristically found in the upper alpha frequency band.

Adult↗
PubMed2001

Event-related desynchronization during anticipatory attention for an upcoming stimulus: a comparative EEG/MEG study.

OBJECTIVES: Our neurophysiological model of anticipatory behaviour (e.g. Acta Psychol 101 (1999) 213; Bastiaansen et al., 1999a) predicts an activation of (primary) sensory cortex during anticipatory attention for an upcoming stimulus. In this paper we attempt to demonstrate this by means of event-related desynchronization (ERD). METHODS: Five subjects performed a time estimation task, and were informed about the quality of their time estimation by either visual or auditory stimuli providing Knowledge of Results (KR). EEG and MEG were recorded in separate sessions, and ERD was computed in the 8-10 and 10-12 Hz frequency bands for both datasets. RESULTS: Both in the EEG and the MEG we found an occipitally maximal ERD preceding the visual KR for all subjects. Preceding the auditory KR, no ERD was present in the EEG, whereas in the MEG we found an ERD over the temporal cortex in two of the 5 subjects. These subjects were also found to have higher levels of absolute power over temporal recording sites in the MEG than the other subjects, which we consider to be an indication of the presence of a 'tau' rhythm (e.g. Neurosci Lett 222 (1997) 111). CONCLUSIONS: It is concluded that the results are in line with the predictions of our neurophysiological model.

Adult↗
PubMed2001

Uncoupling of contingent negative variation and alpha band event-related desynchronization in a go/no-go task.

OBJECTIVES: To examine how the differences in the sequences of brain activation during the go/no-go delayed response choice reaction time (RT) task are reflected into two concurrent methods of measuring brain electrical activity, the alpha band event-related desynchronization (alpha ERD) and the contingent negative variation (CNV). METHODS: alpha ERD and CNV were calculated using appropriate techniques from the same samples of electroencephalographic activity recorded during performance of a cued choice go/no-go delayed response RT task (i.e. S1 (go/no-go)--S2 paradigm) in 8 healthy subjects. RESULTS: All segments of the CNV traces were different in the go and the no-go conditions. The go CNV traces displayed a typical pattern of slow rising negativity reflecting the build-up of attentional resources necessary for adequate performance of the task. On the other hand, the no-go traces remained close to zero reflecting the 'withdrawal' of further preparation after evaluation of S1. During the same period, both go and no-go ERD traces showed a gradual decrease in alpha band power (desynchronization) that was evident until shortly before the presentation of S2. It was only in the 500 ms before S2 presentation that there was any indication that the go and no-go ERD traces were different, but this did not reach statistical significance. CONCLUSIONS: Our data show that the pattern of the go/no-go difference in alpha ERD traces does not correspond to the pattern that can be seen in the CNV traces. This suggests that there is no direct coupling of CNV and alpha ERD, most probably because they measure different aspects of cortical electrical activity. In addition, the extent of the no-go alpha ERD reveals that refraining from performance of a pre-programmed movement is by no means a passive/inactive process.

Adult↗
PubMed2002

Cortical silent period in two patients with meningioma and preoperative seizures: a pre- and postsurgical follow-up study.

OBJECTIVES: Prolongation of the cortical silent period (CSP) following transcranial magnetic stimulation has been reported in patients with partial epilepsy involving the primary motor cortex (M1). This study aimed to investigate the relationship between the expected intraindividual variations in risk factors for seizures and CSP duration. METHODS: We studied a 59-year-old woman with a rolandic meningioma and simple motor partial seizures and a 71-year-old woman with a parietal/occipital meningioma and complex partial seizures. Both patients had seizure as their initial symptom with complete postsurgical remission. Repeated pre- and postoperative CSP recordings were made from both first dorsal interosseous muscles. We compared the results to those obtained in 13 normals. RESULTS: In the patient with simple motor partial seizures, the CSP was significantly prolonged in preoperative recordings and 3 weeks after surgery. This CSP lengthening partly subsided 3 months after surgery. Finally, the CSP was normal 6, 8, and 18 months after surgery. In the patient with complex partial seizures, no CSP change was observed. CONCLUSIONS: In our patient with a rolandic meningioma, CSP prolongation was observed when the risk of seizure relapse was supposed to be higher (preoperative and early postoperative periods). This supports the view that CSP changes reflect compensatory mechanisms in M1 epilepsy.

Adult↗
PubMed2002

On the time resolution of event-related desynchronization: a simulation study.

OBJECTIVES: To investigate the time resolution of different methods for the computation of event-related desynchronization/synchronization (ERD/ERS), including one based on Hilbert transform. METHODS: In order to better understand the time resolution of ERD/ERS, which is a function of factors such as the exact computation method, the frequency under study, the number of trials, and the sampling frequency, we simulated sudden changes in oscillation amplitude as well as very short and closely spaced events. RESULTS: Hilbert-based ERD yields very similar results to ERD integrated over predefined time intervals (block ERD), if the block length is half the period length of the studied frequency. ERD predicts the onset of a change in oscillation amplitude with an error margin of only 10-30 ms. On the other hand, the time the ERD response needs to climb to its full height after a sudden change in oscillation amplitude is quite long, i.e. between 200 and 500 ms. With respect to sensitivity to short oscillatory events, the ratio between sampling frequency and electroencephalographic frequency band plays a major role. CONCLUSIONS: (1) The optimal time interval for the computation of block ERD is half a period of the frequency under investigation. (2) Due to the slow impulse response, amplitude effects in the ERD may in reality be caused by duration differences. (3) Although ERD based on the Hilbert transform does not yield any significant advantages over classical ERD in terms of time resolution, it has some important practical advantages.

Computer Simulation↗
PubMed2002

Probability interrelations between pre-/post-stimulus intervals and ERD/ERS during a memory task.

OBJECTIVES: To investigate the functional relationship between oscillatory electroencephalographic (EEG) components (pre-/post-stimulus intervals) with audio-event-related desynchronization/synchronization (ERD/ERS). METHODS: In an experimental study (9 subjects), the probability-classification analysis of single-trial spectral EEG changes was utilized. Results were compared with auditory ERD/ERS. RESULTS: It was shown that (1) variability of EEG spectral patterns was considerable, (2) EEG activity was different at various task stages, (3) probability measures were different from the results of conventional frequency analysis, (4) probability of trials with alpha- and theta-patterns was characteristically different in various task stages, (5) the occurrence of alpha- and theta-trials were most probable, but not frequent enough to characterize all the trials. The results suggest that the ERD/ERS responses are influenced by EEG characteristics in the pre-stimulus interval, which also have a strong influence on the EEG in the post-stimulus interval. CONCLUSIONS: Alpha- and theta-ERD/ERS responses during memory task performance are not typical for all trials. They reflect EEG changes only in approximately 39% for alpha-activity and approximately 43% for theta-oscillations of all trials, what reflects piecewise stationary EEG structure.

Acoustic Stimulation↗
PubMed2002

Influence of internal globus pallidus stimulation on motor cortex activation pattern in Parkinson's disease.

OBJECTIVES: Indications of the functional neurosurgical treatments become more and more numerous, however, few methods were used to study the mechanism of action and some discrepancies came to light. We assessed the influence of internal globus pallidus (GPI) stimulation and L-Dopa on cortical activation during the preparation and execution phases of the movement compared to clinical improvement of Parkinson's disease. METHODS: We recorded the movement-related cortical potential and movement-related desynchronization. RESULTS: The Unified Parkinson's Disease Rating Scale was improved by 46% under stimulation and 64% under stimulation with L-Dopa. Premovement desynchronization was significantly increased on central contralateral derivation under stimulation with L-Dopa and decreased on frontocentral ipsilateral derivation under stimulation with and without L-Dopa. Movement desynchronization was improved on the contralateral motor cortex under stimulation with and without L-Dopa (benefit correlated with bradykinesia improvement). The movement-related postmotor potential was significantly increased under stimulation with L-Dopa. CONCLUSIONS: GPI stimulation alone influenced the premotor cortex activation during the planning and induced a selective and focal effect on the organisation of motor cortical activity during the movement execution which may explain bradykinesia improvement. The motor cortex activation improvement under stimulation with L-Dopa concerned both the movement preparation and execution but remained very localised to the contralateral motor cortex.

Aged↗
PubMed2002

Effect of discharge desynchronization on the size of motor evoked potentials: an analysis.

OBJECTIVE: Motor evoked potentials (MEPs) after transcranial magnetic brain stimulation (TMS) are smaller than CMAPs after peripheral nerve stimulation, because desynchronization of the TMS-induced motor neurone discharges occurs (i.e. MEP desynchronization). This desynchronization effect can be eliminated by use of the triple stimulation technique (TST; Brain 121 (1998) 437). The objective of this paper is to study the effect of discharge desynchronization on MEPs by comparing the size of MEP and TST responses. METHODS: MEP and TST responses were obtained in 10 healthy subjects during isometric contractions of the abductor digiti minimi, during voluntary background contractions between 0% and 20% of maximal force, and using 3 different stimulus intensities. Additional data from other normals and from multiple sclerosis (MS) patients were obtained from previous studies. RESULTS: MEPs were smaller than TST responses in all subjects and under all stimulating conditions, confirming the marked influence of desynchronization on MEPs. There was a linear relation between the amplitudes of MEPs vs. TST responses, independent of the degree of voluntary contraction and stimulus intensity. The slope of the regression equation was 0.66 on average, indicating that desynchronization reduced the MEP amplitude on average by one third, with marked inter-individual variations. A similar average proportion was found in MS patients. CONCLUSIONS: The MEP size reduction induced by desynchronization is not influenced by the intensity of TMS and by the level of facilitatory voluntary background contractions. It is similar in healthy subjects and in MS patients, in whom increased desynchronization of central conduction was previously suggested to occur. Thus, the MEP size reduction observed may not parallel the actual amount of desynchronization.

Adult↗
PubMed2003

Dynamic synchronisation of central oscillators in essential tremor.

OBJECTIVE: Coherence analysis of electromyography (EMG) signals in essential tremor (ET) suggests that tremor in the right and left arm is induced by independent central oscillators. The sensorimotor cortex seems to be part of the tremor-generating neuronal network in ET. Here, we investigated using electroencephalography (EEG) whether the independence of central oscillators in ET is supported by the analysis of cortical activity. METHODS: In 8 patients with ET, bilateral hand tremor was activated by wrist extension. EMGs from the wrist flexors and extensors were recorded simultaneously with an EEG. EEG-EMG coherence was estimated for 74 epochs of 60 s duration. RESULTS: In 42.6% of the cases, EEG-EMG coherence at the tremor frequency existed only with the contralateral sensorimotor cortex. However, 21.6% of the tremor-EMGs were coherent with EEG activity over both the contralateral and ipsilateral sensorimotor cortex. Bilateral and exclusively contralateral EEG-EMG coherence could alternate within the same recording. Bilateral EEG-EMG coherence was associated with increased right-left EEG-EEG coherence, increased right-left EMG-EMG coherence as well as with increased tremor strength. CONCLUSIONS: In ET, central oscillators in the right and left brain are not entirely independent of each other. They may dynamically synchronise, presumably by interhemispheric coupling via the corpus callosum.

Adult↗
PubMed2003

Exaggerated 16-20 Hz motor cortical oscillation in patients with positive or negative myoclonus.

BACKGROUND: Muscle jerks and their cortical correlates usually occur abruptly and arrhythmically in patients with positive or negative myoclonus. However, there have been several reports in which oscillatory pre-myoclonic cortical discharges occur in patients with repetitive myoclonus (Mov Disord 6 (1994) 633; Brain 119 (1996) 1307; Brain 124 (2001) 2459; Brain 126 (2003) 326). In the present paper, we describe 4 patients with non-repetitive positive or negative myoclonus whose jerks were preceded by 16-20 Hz oscillatory EEG potentials over the contralateral sensorimotor cortex. METHODS: Jerk-locked averaging (JLA) was performed in 3 patients with positive myoclonus two of which had benign familial myoclonus epilepsy whilst the other had tuberculous meningitis. Silent period locked averaging (SPLA) was performed in a patient with hepatic encephalopathy and asterixis. RESULTS: In the 3 patients with positive myoclonus, JLA revealed a sequence of 20 Hz EEG potentials preceding the myoclonus. The positive peak of the last oscillation preceded the onset of myoclonus by the cortico-muscular latency. In the patient with hepatic encephalopahty, SPLA showed that 16 Hz EEG oscillations over the contralateral motor cortex were associated with small EMG oscillations, and that the largest EEG wave of the oscillation preceded the onset of a large EMG discharge just prior to the EMG silence. These oscillatory activities are similar in frequency to the motor cortical oscillations seen in monkeys and humans during voluntary contraction. CONCLUSIONS: Abnormally enhanced rhythmic (16-20 Hz) activities in the motor cortex are associated with arrhythmic positive or negative myoclonus. The rhythmic activities may also be responsible for the generation of the tremulousness (or mini-asterixis) in metabolic encephalopahty.

Adult↗
PubMed2003

EEG activity of aviators during imagery flight training.

OBJECTIVE: Imagery flight training (IFT) is widely used in aviation without neurophysiological evaluation. Electroencephalogram (EEG) during IFT was compared between experienced fighter pilots (FP) and novice pilots (NP). METHODS: Six FP and 9 NP performed imagery right bank, left bank, right roll, and left roll maneuvers. Each task was repeated 5 times in a random order. Instantaneous EEG power was calculated by the intertrial variance method. RESULTS: In FP, 3 waves of event-related desynchronization (ERD) were observed. The third ERD (ERD3) was observed at all the electrode positions except Fp1 which began 0.25 s before the beginning of IFT and reached its peak 0.25 s after the beginning of IFT. In NP, ERD was not related to the start of IFT. The difference in event-related EEG at the peak of ERD3 was not significant between FP and NP. However, the negative change to the peak of ERD3 was significantly larger in FP than in NP. CONCLUSIONS: It is speculated that ERD3 in FP may indicate the activation of cortical areas including visual- and motor-related areas involved in IFT. SIGNIFICANCE: It is speculated that the representation of IFT was programmed in visual- and motor-related cortical areas as an aviator's career advances.

Adult↗
PubMed2004

Human cortical responses during one-bit short-term memory. A high-resolution EEG study on delayed choice reaction time tasks.

OBJECTIVE: We investigated whether a very simple short-term memory (STM) demand induces a visible change of EEG rhythms over the two hemispheres. METHODS: High-resolution EEG was obtained in young adults during two delayed choice reaction time tasks. In the STM condition, a simple cue stimulus (one bit) was memorized along a brief delay period (3.5-5.5 s). The task was visuo-spatial in nature. RESULTS: In the control (NSTM) condition, the cue stimulus remained available along the delay period. Compared to the control condition, the theta power (4-6 Hz) decreased in left frontal and bilateral parietal areas (delay period). Furthermore, low alpha power (6-8 Hz) decreased in bilateral frontal and left parietal areas, while high alpha power (10-12 Hz) decreased in the left fronto-parietal areas. CONCLUSIONS: The decrease of the alpha power is as an expression of the efficient information transfer within thalamo-cortical pathways. The significance of the study stands in the fact that even a very simple STM task (only one bit to be memorized) revealed changes in fronto-parietal theta and alpha rhythms.

Adult↗
PubMed2004

Alpha and beta oscillatory activity during a sequence of two movements.

OBJECTIVE: We studied movement-related electroencephalographic oscillatory changes in the alpha and beta range during a sequence of two movements in 7 healthy volunteers, in order to investigate the relationship between these changes and each component in the sequence. METHODS: The sequence consisted of a wrist active extension-passive flexion followed by a first and second finger pincer. A total of 10.5 s sweeps were recorded using the level of surface electromyographic (EMG) activity in wrist extensors as trigger, including a 7.5 s pre-stimulus. The sweeps were also realigned manually offline using as trigger the end of the first EMG burst, or the beginning of the second movement. An index of the changes in non-phase-locked energy in the 7-37 Hz range was obtained by averaging single-sweep time-frequency transforms. RESULTS: The duration of each of the movements in the sequence and the relationship between them were compatible with the use of two different motor programmes in the sequence. In the beta band, a decrease in energy (event-related desynchronisation, ERD) began 1.5 s before the onset of the first movement, and was sustained until the end of the second movement. No energy increases were observed until the end of the second movement. In the alpha band, the ERD began 0.5 seconds before the first movement and was sustained throughout the recording. CONCLUSION: These findings suggest that the beta-event-related synchronisation is related to the end of the whole motor process, and not to the end of each motor programme.

Adult↗