István Kondákor

Prestimulus EEG microstates influence visual event-related potential microstates in field maps with 47 channels

SummaryThe influence of the immediate prestimulus EEG microstate (sub-second epoch of stable topography/map landscape) on the map landscape of visually evoked 47-channel event-related potential (ERP) microstates was examined using the frequent, non-target stimuli of a cognitive paradigm (12 volunteers). For the two most frequent prestimulus microstate classes (oriented left anterior-right posterior and right anterior-left posterior), ERP map series were selectively averaged. The post-stimulus ERP grand average map series was segmented into microstates; 10 were found. The centroid locations of positive and negative map areas were extracted as landscape descriptors. Significant differences (MANOVAs and t-tests) between the two prestimulus classes were found in four of the ten ERP microstates. The relative orientation of the two ERP microstate classes was the same as prestimulus in some ERP microstates, but reversed in others. — Thus, brain electric microstates at stimulus arrival influence the landscapes of the post-stimulus ERP maps and therefore, information processing; prestimulus microstate effects differed for different post-stimulus ERP microstates.

Characteristic Distribution of Interictal Brain Electrical Activity in Idiopathic Generalized Epilepsy

Summary:  Purpose: To demonstrate the anatomic localization of the cortical sources of the interictal EEG activity in human idiopathic generalized epilepsy (IGE).

Global dimensional complexity of multichannel EEG in mild Alzheimer's disease and age-matched cohorts.

Multichannel EEG as sequence of momentary brain field maps constitutes a trajectory through K-dimensional state space (K = number of channels); the complexity of this trajectory is assessed by the nonlinear measure of global correlation dimension (Global Dimensional Complexity, GDC) with the number of electrodes as embedding dimension. We analyzed eyes-closed EEG of three age-matched subject groups: mild Alzheimers disease (AD; n = 21), mild cognitive impairment (29) and subjective memory complaint (29). Kruskal-Wallis statistics showed an overall effect between groups. AD patients differed significantly (GDC = 4.56) from mild cognitive impairments (GDC = 4.98) and from subjective memory complaints (GDC = 4.93). GDC also had significant positive correlations with mental condition and performance (MMSE and WAIS-R scores). Thus, the dynamics of brain state development over time in mild AD differs from that in mild cognitive impairment and in subjective memory complaint cases.

Smell and taste of chewing gum affect frequency domain EEG source localizations

We investigated brain electric field signatures of subjective feelings after chewing regular gum or gum base without flavor. 19-channel eyes-closed EEG from 20 healthy males before and after 5 minutes of chewing the two gum types in random sequence was source modeled in the frequency domain using the FFT-Dipole-Approximation. 3-dimensional brain locations and strengths (Global Field Power, GFP) of the equivalent sources of five frequency bands were computed as changes from pre-chewing baseline. Gum types differed (ANOVA) in pre-post changes of source locations for the alpha-2 band (to anterior and right after regular gum, opposite after gum base) and beta-2 band (to anterior and inferior after regular gum, opposite after gum base), and of GFP for delta-theta, alpha-2 and beta-1 (regular gum: increase. gum base: decrease). Subjective feeling changed to more positive values after regular gum than gum base (ANOVA).--Thus, chewing gum with and without taste-smell activates different brain neuronal populations.

Chewing-gum flavor affects measures of global complexity of multichannel EEG.

Global complexity of spontaneous brain electric activity was studied before and after chewing gum without flavor and with 2 different flavors. One-minute, 19-channel, eyes-closed electroencephalograms (EEG) were recorded from 20 healthy males before and after using 3 types of chewing gum: regular gum containing sugar and aromatic additives, gum containing 200 mg theanine (a constituent of Japanese green tea), and gum base (no sugar, no aromatic additives); each was chewed for 5 min in randomized sequence. Brain electric activity was assessed through Global Omega (Omega)-Complexity and Global Dimensional Complexity (GDC), quantitative measures of complexity of the trajectory of EEG map series in state space; their differences from pre-chewing data were compared across gum-chewing conditions. Friedman Anova (p < 0.043) showed that effects on Omega-Complexity differed significantly between conditions and differences were maximal between gum base and theanine gum. No differences were found using GDC. Global Omega-Complexity appears to be a sensitive measure for subtle, central effects of chewing gum with and without flavor.

Single-dose piracetam effects on global complexity measures of human spontaneous multichannel EEG

Global complexity of 47-channel resting electroencephalogram (EEG) of healthy young volunteers was studied after intake of a single dose of a nootropic drug (piracetam, Nootropil UCB Pharma) in 12 healthy volunteers. Four treatment levels were used: 2.4, 4.8, 9.6 g piracetam and placebo. Brain electric activity was assessed through Global Dimensional Complexity and Global Omega-Complexity as quantitative measures of the complexity of the trajectory of multichannel EEG in state space. After oral ingestion (1-1.5 h), both measures showed significant decreases from placebo to 2.4 g piracetam. In addition, Global Dimensional Complexity showed a significant return to placebo values at 9.6 g piracetam. The results indicate that a single dose of piracetam dose-dependently affects the spontaneous EEG in normal volunteers, showing effects at the lowest treatment level. The decreased EEG complexity is interpreted as increased cooperativity of brain functional processes.

Spectral characteristics and linear-nonlinear synchronization changes of different EEG frequency bands during the CNV.

During the CNV recorded in a simple auditory working memory task, task-specific decrease of the relative delta band and a transient increase of the absolute theta band were seen, accompanied by an increase of the absolute alpha1 and alpha2 bands in the posterior region. The decreased delta power probably corresponds to increased task-evoked arousal, whereas the transient theta power increase corresponds to working memory demand and possibly to the orienting response. The increased alpha1 and alpha2 power may be a manifestation of a top-down mechanism revealing control over the execution of a response. The area-specific, task-related, and frequency-dependent changes of EEG complexity measures indicate frontally increasing complexity during the early part of the CNV in the beta frequency bands, which underscores the importance of this region in the mechanisms of anticipatory behavior.

Distribution of Spatial Complexity of EEG in Idiopathic Generalized Epilepsy and Its Change After Chronic Valproate Therapy

Summary:The objective of this study was to investigate the global and regional spatial synchrony of the EEG background activity, and to assess the effect of chronic valproate therapy on spatial synchrony. 15 idiopathic generalized epilepsy (IGE) patients were examined and compared to 16 normal controls. Resting EEG with 19 channels was investigated before and during chronic administration of valproate (VPA). Omega, a single-valued measure of spatial covariance complexity, was calculated to assess the degree of spatial synchrony of EEG. Furthermore, a new parameter was defined to characterize the distribution of spatial synchrony (Antero-Posterior Complexity Ratio, APCR). Global Omega complexity was significantly lower in IGE compared to controls, while regional complexity showed significant differences only in the anterior region: the IGE group showed lower complexity. APCR was significantly lower in IGE. VPA therapy (1) lowered the global complexity, (2) increased regional complexity in the anterior region, but decreased it in the posterior region, and (3) increased APCR. In IGE lower complexity, i.e. enhanced spatial synchrony, was found, especially in the anterior cortical area. VPA modified the distribution of spatial synchrony in IGE patients towards that of normal controls, although the effect is not identical with full normalization of cortical bioelectric activity. Whether the observed change of spatial synchrony distribution may reflect the normalizing effect of valproate on the brain state is worth further investigation.

Valproate treatment normalizes EEG functional connectivity in successfully treated idiopathic generalized epilepsy patients

AIM To investigate the effect of chronic VPA treatment of EEG functional connectivity in successfully treated idiopathic generalized epilepsy (IGE) patients. PATIENTS AND METHODS 19-channel waking, resting-state EEG records of 26 IGE patients were analyzed before treatment (IGE) and after the 90th day of treatment (VPA), in seizure-free condition. Three minutes of artifact-free EEG background activity (without epileptiform potentials) was analyzed for each patient in both conditions. A group of 26 age-matched healthy normative control persons (NC) was analyzed in the same way. All the EEG samples were processed to LORETA (Low Resolution Electromagnetic Tomography) to localize multiple distributed sources of EEG activity. Current source density time series were generated for 33 regions of interest (ROI) in each hemisphere for four frequency bands. Pearson correlation coefficients (R) were computed between all ROIs in each hemisphere, for four bands across the investigated samples. R values corresponded to intrahemispheric, cortico-cortical functional EEG connectivity (EEGfC). Group and condition differences were analyzed by statistical parametric network method. MAIN RESULTS p<0.05, corrected for multiple comparisons: (1) The untreated IGE group showed increased EEGfC in the delta and theta bands, and decreased EEGfC in the alpha band (as compared to the NC group); (2) VPA treatment normalized EEGfC in the delta, theta and alpha bands; and (3) degree of normalization depended on frequency band and cortical region. CONCLUSIONS VPA treatment normalizes EEGfC in IGE patients.

EEG functional connectivity of the intrahemispheric cortico-cortical network of idiopathic generalized epilepsy.

AIMS Intrahemispheric, cortico-cortical EEG functional connectivity (fC) was investigated in untreated patients with idiopathic generalized epilepsy (IGE) in this explorative study. PATIENTS AND METHODS Group comparison was carried out between 19, drug-naive IGE patients and 19, matched healthy persons. 90×2s of 19 channels waking, interictal background EEG signal (without epileptiform potentials) were processed to the LORETA (low resolution electromagnetic tomography) software to compute current source density for 2394 voxels representing parcels of the cerebral cortex for 25 very narrow bands of 1Hz bandwidth (VNBs) from 1 to 25Hz. EEG fC was investigated among the already localized sources. Pearson correlation coefficients (R) were computed among the 33 regions of interest (ROI) within the left and within the right hemisphere, separately. Group differences were computed by means of t-statistics. Corrected p<0.05 differences were accepted as statistically significant. MAIN RESULTS (1) The anatomical patterns of the fC differences showed great frequency-dependency. (2) Hemispheric asymmetry was prominent within most VNBs. (3) Decreased fC in the IGE group was found across all VNBs in the 1-6Hz frequency range as compared to mixed patterns comprising both increased and decreased fC at >6Hz frequencies. (4) In the 5-25Hz range, decreased fC dominated in the anterior, increased fC in the posterior parts of the cortex. (5) The results delineated an anterior and a posterior network. DISCUSSION (1) Decreased fC in the 1-6Hz band might indicate some relationship to yet hidden structure network abnormalities. (2) The anatomical patterns of fC indicate frequency-dependent, pathological coupling and decoupling processes in the interictal state. (3) The two networks might help to understand seizure liability and seizure precipitation in IGE. SIGNIFICANCE This is the first study to explore EEG fC in the interictal condition of IGE patients. The importance of EEG frequencies in evaluating fC in IGE was demonstrated and starting points for further research were given.