Oliver Filz

Artifact processing in computerized analysis of sleep EEG - a review.

Quantitative analysis of sleep EEG data can provide valuable additional information in sleep research. However, analysis of data contaminated by artifacts can lead to spurious results. Thus, the first step in realizing an automatic sleep analysis system is the implementation of a reliable and valid artifact processing strategy. This strategy should include: (1) high-quality recording techniques in order to minimize the occurrence of avoidable artifacts (e.g. technical artifacts); (2) artifact minimization procedures in order to minimize the loss of data by estimating the contribution of different artifacts in the EEG recordings, thus allowing the calculation of the ‘corrected’ EEG (e.g. ocular and ECG interference), and finally (3) artifact identification procedures in order to define epochs contaminated by remaining artifacts (e.g. movement and muscle artifacts). Therefore, after a short description of the types of artifacts in the sleep EEG and some typical examples obtained in different sleep stages, artifact minimization and identification procedures will be reviewed.

Calculation of event-related coherence—A new method to study short-lasting coupling between brain areas

SummaryThis article deals with the estimation of event-related coherence (ERCoh) and its application to the planning and execution of self-paced index finger movement. ERCoh estimation complements the event-related desynchronization (ERD) measurements of rhythms within the alpha band. ERCoh yields information of the functional relationships between different brain areas as a function of time. The time resolution is 125 msec. Before movement onset a contralateral ERCoh increase was found between premotor and motor areas. This coherence increase was accompanied by an ERCoh decrease in parallel to the ERD over the contralateral centro-temporal areas. During movement, the ERD became bilaterally symmetrical. Simultaneously, interhemispheric coherence between contralateral and ipsilateral sensori-motor areas increased.

Topology of EEG Coherence Changes May Reflect Differential Neural Network Activation in Cold and Pain Perception

Pain perception in the brain can be analyzed by neuroimaging (PET, fMRI) and electrophysiological parameter mapping (EEG, ERP/MEG, MEF). These studies have generally been focused on the localization of cerebral activation. Whether pain can be conceptualized as localized function or best be understood by distributed function is important to the theory of human pain processing in the brain. Here, we report that cold and pain perception in the brain is characterized by webs of EEG coherence changes which may reflect coupling or de-coupling of different cortical areas during cold and pain processing. EEG was recorded during cold and pain perception (right hand immersion in 15°C cool-water vs. 0.3°C ice-water for 3 min.) with eyes opened. Subjects rated the cold perception at 2.3 (cool to cold, but no pain) and the pain perception at 6.7 (moderate-strong pain) in a 1-10 scale. The obtained EEG spectral parameters were compared with the corresponding parameters of the resting baseline using paired Wilcoxon tests in the sense of statistical filters to depict those differences which differ clearly from changes by chance. The results were presented in probability maps. The EEG results indicated highly differential coherence networks between cold and pain perception. The cold perception was characterized as decreased coherence in the theta band mainly between frontal electrodes and increased interhemispheric coherence in the alpha range mainly between central and frontal positions. During pain perception almost no coherence changes in the theta band were observed, but great coherence increase in the delta band between central, parietal and frontal electrodes. The network of coherence changes in the alpha band showed strong involvement of electrode C3 concerning coherence increases with frontal positions. In the beta-1 band coherence increase within the left hemisphere was much more pronounced during pain than during cold. The differential characteristics of EEG coherence changes based on neural networks and their spatial organization in the neocortex indicate the distributed brain processing between cold and pain perception in man. This study may contribute to our understanding of the large scale neural networks in cognition based on neurophysiological binding hypothesis and network connections of neural ensembles.

EEG aspects of mentally playing an instrument

This pilot study examines the possibility to detect activities of SMA by means of EEG coherence analysis in a female professional violoncellist. The proband was asked, for 5 min each, to listen to a piece of music (she knew by heart), to imagine playing this piece and to imagine playing scales. The experiment was repeated after 5 days. Consistent significant coherence changes with respect to the averaged EEG at rest were plotted as probability maps. For each of these three tasks different coherence patterns emerged. Among the electrodes next to SMA, Fz was most involved while playing scales, less while imagining playing the same piece and still less while just listening to it.

The Dependence of Coherence Estimates of Spontaneous EEG on Gender and Music Training

This study examined differences in the spontaneous electroencephalographic (EEG) signal in terms of music training and gender. Coherence estimates obtained by spectral analysis provided an efficacious method to study these differences. In the first study, differences in the spontaneous EEG between subjects with and without music training were observed. Subjects with music training exhibited significantly higher coherence values both within and between cerebral hemispheres when compared with subjects without music training. The most striking differences were observed in the two lowest (delta and theta) and two highest (beta 1 and beta 2) bands, with differences in the temporoparietal regions of both hemispheres being most prominent. The findings are discussed in terms of specialized organization of brain activity that influences cortical connectivity. Using the same method, differences in spontaneous EEG were also found between male and female subjects. Females tended to have significantly higher interhemispheric coherence values when compared with males. Both findings are also supported by recently discovered anatomic differences.

The Reflection of Cognitive Tasks in EEG and MRI and a Method of Its Visualization

SummaryUp until recently, neurology was dominated by localisatory thinking. Language and other so-called“centers” were considered to be centers of command controlling the respective functions. Today, there is general agreement that, instead, for every brain function numerous brain regions must act together. For the exploration of these manifold topographic cooperations produced by cognitive tasks, coherence of long-term EEG periods proved to be a proficient parameter for the representation of functionally essential connections. Because of the unequivocal meaningfulness of absolute coherence values, instead, only the signs of significant differences between coherence values during cognitive tasks and periods of EEG at rest before and after the task were considered for all possible electrode pairings and charted on schematic maps of the brain. In addition, the signs of significant changes of amplitude were entered. This procedure was performed for each of 6 frequency bands and for the 19 electrodes of the 10/20 system, thus yielding 171 possible plus or minus values for coherence and 19 for amplitude, respectively. The positions of the electrodes were marked by an MRI contrast medium. After the EEG, MRI examination was performed. The MRI data were segmented and the cortex was mapped onto a plane using a method similar to cartography. The exact electrode positions are registered from a similarly obtained map of the scalp and the electrode position pattern is used as basis for the coherence graphs. A detailed map of the cortex based on the segmented MRI data with the electrode positions marked is provided as a reference enabling allocation of the electrodes to the cortical structures. The usefulness of this procedure is demonstrated with a single subject by means of different cognitive tasks including musical thinking.

EEG in Music Psychological Studies

One of the main aims of the present paper is to comment upon why the EEG seems to be such a promising tool to glimpse - generally speaking — into the fabrics of thinking, the “enchanting loom” as Sherrington formulated it so poetically and so soundly. In addition to that, two special issues concerning music and EEG are briefly discussed: hemispheric lateralization and musical expectancy. Further topics concerning the processing of music by the brain, among these the question of the consistency of our findings are the subject of another paper (Richter et al., this volume).

How Consistent are Changes in EEG Coherence Patterns Elicited by Music Perception

One of the aims of this symposium is to emphasize that multidisciplinary research is a good approach to the study of musical cognition. In addition to a variety of psychological methods and studies of neurological or psychiatric diseases, neurophysiological approaches may further contribute to this subject, making use of the registration and evaluation of the ongoing electrical activity of the brain.