The effect of brain function on coherence patterns in the bipolar EEG

An EEG Study of a Confusing State Induced by Information Insufficiency during Mathematical Problem-Solving and Reasoning

Confusion is a complex cognitive state that is prevalent during learning and problem-solving. The aim of this study is to explore the brain activity reflected by electroencephalography (EEG) during a confusing state induced by two kinds of information insufficiencies during mathematical problem-solving, namely, an explicit situation that clearly lacked information and an implicit situation in which the missing information was hidden in the problem itself, and whether there is an EEG difference between these two situations. Two experimental tasks and three control tasks were created. Short time Fourier transformation (STFT) was used for time-frequency analysis; then the alpha task-related-power (TRP) changes and distributions, which are closely related to cognitive processing, were calculated, and repeated measures ANOVA were performed to find the significant difference between task conditions. The results showed that the alpha power decreased significantly in the regions related to calculation when the participants encountered both explicit and implicit information insufficiency tasks compared to the control tasks, suggesting that confusion can cause more brain activity in the cortical regions related to the tasks that induce confusion. In addition, the implicit information insufficiency task elicited more activity in the parietal and right temporal regions, whereas the explicit information insufficiency task elicited additional activity in the frontal lobe, which revealed that the frontal region is related to the processing of novel or unfamiliar information and the parietal-temporal regions are involved in sustained attention or reorientation during confusing states induced by information insufficiency. In conclusion, this study has preliminarily investigated the EEG characteristics of confusion states, suggests that EEG is a promising methodology to detect confusion, and provides a basis for future studies aiming to achieve automatic recognition of confusing states.

Frequency domain simultaneous source and source coherence estimation with an application to MEG

Interactions between cortical areas are crucial for cognitive functioning. Methods currently in use to assess such interactions are not well suited for this task because they lack timing precision, localization precision, or both. We present a method for simultaneous estimation of source location and orientation parameters and cross-spectral parameters to overcome these problems. Different estimators are evaluated for their performance. From a simulation study, we conclude that the estimators derived from the maximum-likelihood procedure have good statistical properties with moderate sample sizes, whereas those obtained from the generalized least squares procedure are biased and give poor-quality standard errors. The method is illustrated with visually evoked field data, with inconclusive results.

EEG coherence and reference signals: experimental results and mathematical explanations

Coherence has become an essential tool in the description of functional relationships between EEG signals generated within various brain areas. In EEG coherence analysis, the reference signal has an important influence, as an improper reference can distort the results and make them impossible to interpret. In the study, EEG are recorded from one volunteer in 11 sessions, with electrodes selected according to the international 10-20 system against FCz. Additional electrodes are placed on the nose, chin and left and right ear lobes, and recordings are made also against FCz. This enables re-referencing of the stored EEG signals for different reference sites, averaged reference signals, common average reference, Laplacian and bipolar. Coherence values using single reference electrodes depend on the reference site to a large extent. Reliable results are obtained using averaged non-cephalic signals as reference ([A1 + A2]/2). Coherence based on FCz yields slightly lower or higher values than that based on non-cephalic reference sites. Completely different results yield common average reference recordings, Laplacian and bipolar recordings, probably owing to the cancellation effect of essential signal portions using these techniques. A mathematical model for coherence based on signal-to-noise ratios is introduced to explain the experimental findings: the model demonstrates that noisy reference signals lead to coherence increase, whereas a coherent amount in the reference signal leads to coherence decrease.

Timing of puberty and EEG coherence during photic stimulation

Selective elimination of a large proportion of cortical synapses constitutes the last major stage in brain development which is linked to sexual maturation. Various neurodevelopmental theories have proposed an association between schizophrenia and late brain maturational events. Based on epidemiological and psychopharmacological data, Saugstad hypothesised a relationship between timing of puberty, synaptic density and psychosis proneness. Early puberty should result in an earlier end to synaptic pruning, a larger number of surviving connections and an increased risk for affective psychosis. In contrast, in late maturers prolonged synapse elimination should lead to lower synaptic density which constitutes a diathesis for schizophrenia. We used EEG coherence as a neurophysiological measure of cortico-cortical connectivity. Late maturers were expected to show higher coherence, especially for short-distance connections where lower synaptic density should lead to decreased local differentiation. EEG was recorded from 12 bipolar derivations in 19 early and 19 late maturing subjects of both sexes under conditions of rest and photic stimulation at different flicker frequencies. Whereas there were no coherence differences between early and late maturers during rest, both groups differed during flicker stimulation. As hypothesised, late maturers were found to have higher short-distance coherence. Late maturers were also found to have higher intrahemispheric long-distance coherence. These findings were restricted to delta, alpha and beta 2 bands and were more pronounced in males. Our findings are interpreted in terms of a structural difference in neuronal connectivity between extreme early and late maturers.