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Evoked Coherences of EEG in Mental Load: An Investigation in Chess Players
Abstract
The present work investigates the validity of evoked coherences of the EEG as an indicator of mental load. Previous studies have shown that coherences of EEG, generally, react sensitively to subtle changes of a subject's mental date. Instead of the usually calculated ,,steady-state" values, the present study used evoked coherences, that, like evoked potentials, reflect neural information processing in the context of discrete events. Considering the well-known difficulties with the induction of mental load in laboratory conditions, especially in connection with EEG recording, chess playing was chosen as a model of mental activity. Chess diagrams of different complexity were presented for solution to 25 active members of chess clubs. For a differentiation between cognitive and perceptive load, a number of diagrams was provided with visual noise, which hampered recognition. Evoked coherences of EEG showed highly significant differences, nor only between perceptive and cognitive load, but also between different cognitive operations. In our experiment, perceptive load was reflected in the Theta frequency range, whereas cognitive load was reflected in Beta. A two-staged factor analysis procedure, in connection with a topological analysis, allowed the definition of cortical areas participating significantly in the discrimination of different conditions. The results were confirmed in a re-test study. Evoked coherences of EEG, thus, represent a sensitive tool for the investigation of mental load.
... This paper presents a pilot study on the differences in evoked EEG coherence measures (computed as zero-lagged cross-correlation, "EC") between chess experts and novices while solving chess problems. One of our earlier investigations (Volke, 1999) had shown that both location and direction of EC changes in task processing (compared with a resting condition) depend on the degree of task performance. As a result we postulated that when solving the same tasks experts and novices would show different EC. ...
... In a more recent study (Volke et al., 1999), we investigated the evoked EEG coherence during the solution of different types of chess tasks. Significant differences were found between the coherence patterns, depending on the complexity of the task types. ...
This paper presents a pilot study on the differences in evoked EEG coherence measures (computed as zero-lagged cross-correlation, “EC”) between chess experts and novices while solving chess problems. One of our earlier investigations (Volke, 1999) had shown that both location and direction of EC changes in task processing (compared with a resting condition) depend on the degree of task performance. As a result we postulated that when solving the same tasks experts and novices would show different EC. The results of the recent study confirmed this supposition. Chess tasks of varying difficulty were presented to 25 chess players of different performance levels. The EEG was recorded from 29 positions (enhanced 10:20-system). EC were computed for post-stimulus intervals of 1.6s. A special averaging procedure (considering Fisher's Z transformation) was applied for summarizing the single EC of each type of task. These subject- and task-related EC-values (29 × 28/2 = 406 values per frequency band) were subjected to a MANOVA after a two-staged principal component analysis. Significant differences between experts and novices, compared with the resting condition, were found in the delta frequency range. The relevant cortical areas of experts, defined by a topological analysis of the differentiating principal components, were located rather posterior and more in the right hemisphere, compared with those of the novices. Furthermore, the essential EC of the experts showed higher values in the task situation (“on-coupling”), compared with the resting condition, whereas those of the novices were lower (“off-coupling”). The results are interpreted as a higher task-related functional integration of the cortical areas in experts.
... An increased quantity of visual noise emanating from a number of irrelevant or unwanted stimuli can increase the load on processing capacity. When the load on processing capacity is increased (particularly through visual noise), advertisement message distortion increases (Volke, Dettmar, Richter, Rudolph, & Buhss, 1999). ...
... Um campo bastante promissor para a medição da Carga Cognitiva tem sido a utilização de imagens neurológicas obtidas por meio da tomografia por emissão de pósitrons 53 (PET) e também por meio da ressonância magnética (VOLKE et al. 1999;GERLICK e JAUSOVEC, 1999;MURATA, 2005 Embora esse método seja rotineiramente utilizado para visualizar regiões do cérebro ativadas em estudos sobre a Memória de Trabalho envolvendo tarefas simples, tais como a memorização de palavras, compreensão de sentenças ou rotações visuais, ainda é inconclusivo para o estudo de processos de aprendizagem complexos e a conexão entre a carga sobre a Memória de Trabalho e a atividade no córtex préfrontal ainda não é completamente compreendida. Além do mais, a complexidade técnica do aparato de medida e as limitações práticas da duração e frequência dessas medições dificultam o seu uso em uma situação real de aprendizagem. ...
Como as limitações da Memória de Trabalho afetam o modo como se aprende,
devem também, por óbvio, condicionar o modo como se ensina. A Teoria da Carga
Cognitiva, tendo em vista essas limitações, oferece 29 diretrizes sobre como elaborar
um ensino que diminua a Carga Cognitiva improdutivae, ao mesmo tempo, maximize a
Carga Cognitiva produtiva para tornar a aprendizagem mais eficiente. Todas essas
diretrizes fundamentam-se em experiências cientificas, não sendo, portanto, meros
construtos teóricos. Embora a aplicação dessa Teoria seja de grande utilidade, existe um
vazio na literatura acadêmica em língua portuguesa com relação a sua origem,
desenvolvimento e aplicações. Esta dissertação reúne e disponibiliza os conhecimentos
empíricos, teóricos e metodológicos acumulados sobre essa teoria, os quais são expostos
historiando-se a origem e o desenvolvimento teórico/experimental das suas principais
diretrizes, dos três tipos de Cargas Cognitivas (Intrínseca, Estranha e Relevante), e das
“descobertas” dos Efeitos da Teoria da Carga Cognitiva: Efeito da Atenção Dividida,
Efeito Modalidade, Efeito da Redundância, Efeito do Exemplo Resolvido e Efeito
Reverso. Esta dissertação foi elaborada para ser utilizada por professores, pesquisadores
e, por óbvio, professores-pesquisadores, sendo particularmente útil àqueles professores
que necessariamente utilizam a "resolução de problemas" como parte de sua prática
pedagógica.
... It is to be assumed that this theta over beta ratio mismatch is by itself rather a symptom of more fundamental underlying neuronal processes. It was shown that this ratio mismatch of the two frequency components is due to a lack in synchronization of cognitive feedback loops [37,38] (Barry et al., 2002; Chabot & Serfontein, 1996) Therefore ADHD patients suffer from the ability to adapt action pursuing and action controlling resp. correcting process to each other. ...
An EEG-Based audiovisual stimulation system was tested on a group of 32 ADHD patients. The efficacy was compared
in a pre- and post analysis over a treatment period of 3 month with a control group and a group of patients with an EEGbased
neurofeedback therapy. The number of impulsivity errors in a stop-signal paradigm at several distinct times during
and after the therapy was used as a quality marker. The main feature of this method uses real-time-EEG data derived parameters
for a controlled manipulation of EEG patterns with persistently strong audio-visual stimuli. It is based upon a
direct feedback of changes in short-term coherences in the context of central nervous stimulus processing to control the
stimulating frequency. The real-time EEG processing is done on the basis of time-dependent coherence analysis of the
theta and beta band.
... Cognitive load can also be assessed by using neuro-imaging techniques. Though this is a promising field (see e.g., Gerlic and Jausovec 1999; Murata 2005; Smith and Jonides 1997; Volke et al. 1999) there are still questions on how to relate brain activations precisely to cognitive load. Overall, physiological measures show promise for assessing cognitive load but (still) have the disadvantage of being quite intrusive. ...
Cognitive load is a theoretical notion with an increasingly central role in the educational research literature. The basic
idea of cognitive load theory is that cognitive capacity in working memory is limited, so that if a learning task requires
too much capacity, learning will be hampered. The recommended remedy is to design instructional systems that optimize the
use of working memory capacity and avoid cognitive overload. Cognitive load theory has advanced educational research considerably
and has been used to explain a large set of experimental findings. This article sets out to explore the open questions and
the boundaries of cognitive load theory by identifying a number of problematic conceptual, methodological and application-related
issues. It concludes by presenting a research agenda for future studies of cognitive load.
KeywordCognitive load theory
... In an investigation of task-evoked EEG coherence during the solution of different types of chess tasks, a recent study [Volke et al., 1999] showed significant differences between the coherent patterns, which depend primarily on the complexity of the task. Simple and well-mastered tasks are accompanied usually with increased coherence between cortical regions, whereas poorly mastered tasks are accompanied with decreased coherence or desynchronization. ...
Our primary question was to learn whether mentally composing drawings of their own choice produce different brain electric features in artists and laymen. To this purpose, we studied multichannel electroencephalograph (EEG) signals from two broad groups (all participants were females): artists (professionally trained in visual arts) and non-artists (without any training in art). To assess the underlying synchronization, which is assumed to be the platform for general cognitive integration between different cortical regions, three measures inspired by nonlinear dynamical system theory were applied as follows: (1) index based on generalized synchronization; (2) index based on mean phase coherence; and (3) index of phase synchrony based on entropy. Results consistent over all three measures were as follows: comparing the tasks to rest, the artists showed significantly stronger short- and long-range delta band synchronization, whereas the non-artists showed enhancement in short-range beta and gamma band synchronization primarily in frontal regions; comparing the two groups during the tasks, the artists showed significantly stronger delta band synchronization and alpha band desynchronization than did the non-artists. Strong right hemispheric dominance in terms of synchronization was found in the artists. In artists, the higher synchrony in the low-frequency band is possibly due to the involvement of a more advanced long-term visual art memory and to extensive top-down processing. The results demonstrate that in artists, patterns of functional cooperation between cortical regions during mental creation of drawings were significantly different from those in non-artists.
Various studies on ADHD patients come to the conclusion that in the spontaneous EEG the low frequency theta-band (4-7Hz) is increased, whereas the beta-(14-18 Hz), alpha-band and the sensorimotor rhythm (SMR) is decreased compared to healthy volunteers. [1;2;3]. Therefore the theta/beta-ratio is considered to be a good indicator for the diagnosis of ADHD also shown in standardized behavioral studies. [4].
It was therefore not too far fetched to utilize neurofeedback - training for ADHD treatments using the theta/beta-band ratio as a parameter at first.
But the application of neurofeedback methods for the ADHD therapy showed ambivalent results: whereas some studies concluded the evidence for the effectiveness of the method for children not responding to medical therapy, [5; 6; 7], other studies state no improvements of hardware – in – the – loop – technique compared to pharmaceutical treatment [8; 9]
Of a more serious concern regarding the neurofeedback method could possibly be that the method requires a degree of concentration and learning ability, which is actually lacking in this group.
The in part one [42] introduced method of evoked coherences was used in search for independent signs of the levels of processing effects on memory performance. 9 subjects in a visual pilot study and 16 subjects in the acoustic main experiments were presented 30 words each in a perceptive, semantic and metacognitive orientation condition. A 16-channel-EEG was recorded and stimulus-related time-variant spectral components (5, o, a, ) were calculated for analysis of evoked coherence. In order to differentiate between task processing and general functional state of the brain in the main study one series of experimental conditions was carried out in the state of deep relaxation (trance). The evoked coherences were tested with multi-factorial ANOVA and contrasted by Sc/ieffe-test. As expected, the variation in the state of the consciousness was related with strong but diffuse changes in power and coherence spectra. In contrast to this, differences in level of processing were accompanied by specific focal patterns of evoked coherence with nearly no changes in power. Especially in the lower frequency bands there appeared differentiating coherences between posterior regions and single points of the frontal and left-temporal regions of the cortex. The data also supported the interpretation that deeper processing is characterized by a functional de-coupling of activity in progressively more anteriory located regions and within lower frequency band, particularly 5.
The present study was performed to investigate correlations between creativity and EEG parameters. For this purpose a creativity-test (consisting of four subtests) was applied to twenty male and eighteen female volunteers, which rates wealth of imagination and creative power ('Gestaltungsvermogen'). The EEG were recorded during the performance of these tests (the mental attainments of the probands were noted down after the recordings) so that the obtained EEG-data could be directly correlated to the scores of the creativity-test. The EEG recordings were made from nineteen electrodes (10/20-system), six frequency bands from 1.5 to 31.5 Hz were considered for the evaluation. The parameters amplitude and coherence (between all nineteen electrodes) were computed. Significant rank-correlations were found only for coherence values, not for amplitude. Striking sex differences are shown: the correlation between test-scores and coherence were primarily negative for the female, yet primarily positive for the male probands. These results are rather consistent with former studies concerning spatial imagination abilities and EEG-parameters. As an explanation for these findings the assumption of different cortical organisation in males and females is discussed, possibly due to hormonal influence.
In 20 subjects of both gender we examined the question whether electrophysiological correlates of mental imagery can be detected using amplitude/coherence analysis. 40 concrete words denoting objects were presented to the subjects both visually and acoustically for 2 s each, with the only instruction of attentively perceiving the stimulus. The careful interview afterwards revealed that in some subjects hearing or reading a word had provoked prompt, automatic and detailed mental images of the object, whereas in others not. This differentiation (visualizers - non visualizers) was used to make a comparison between EEG changes elicited by visualization of a word and EEG changes elicited by perceiving the word without visualizing it. Since a subject with visual imagery while reading the words not necessarily had visual imagery while hearing them, both groups are independent in this respect; thus differences in the EEG changes of visualizers versus non-visualizers for one task (visually) need not necessarily be the same in the other (acoustically). If we nevertheless would find repeating differences, this would strengthen the evidence that they reflect the process of visualization. The EEG was recorded according to the 10/20 system with respect to averaged signals of both ear lobes. Amplitude and coherence were computed for the frequency ranges θ to β3; significant de- and increases between each task (visually, acoustically) and a resting condition with eyes opened were mapped. Comparing the maps 'acoustically - eyes opened' and 'visually - eyes opened' reveals different EEG changes for the two modalities; dividing each task into two subgroups of 'visualizers' and 'nonvisualizers' reveals differences between the groups for each of the tasks. We here only report about the differences between these two subgroups: 1.) During reading as well as during listening to words the group of subjects in which the words had elicited mental images in the mean shows higher frontal coherence increases than the control group (fig. 2). 2.) A statistical group comparison reveals significantly higher β-amplitude in the occipital region in the group of visualizers: this equally applies for both tasks (visually, acoustically) (fig. 4). 3). β1-coherence in the group of visualizers is significantly lower in the occipital region in both tasks (fig. 3). These results show that mental imagery is correlated with frontal as well as with occipital EEG changes and therefore support other findings, demonstrating that mental visualization is partly evolved in visual areas and partly in frontal, association areas.
Using factor and discriminant analysis, it has been investigated wether coherence-related parameters of EEC are suitable for the detection of early impairments of brain functions, caused by low toxic expositions. This and related questions are of increasing importance in so far, as humans, within modern industrial society, are continuously exposed to a large and still growing number of "subcritical" noxes, the long-term and combined effects of which are as yet widely unknown. A remarkable position within the large spectrum of these substances is held by neurotoxins. From this situation, a demand results for related effective diagnostic methods. 14 long-term and 14 median-term CS2-exposed subjects and two age-matched control groups were examined. The EEC was derived from 16 positions (reduced 10:20 system) under resting condition. The coherence parameters were defined in accordance with the classical EEC frequency ranges, using the time-variant spectral analysis (36). From a factor analysis, two factors emerged within the Alphaand the Theta range, reflecting shifts of coherence mainly in the frontal (first) and the occipital areas (second factor). A satisfactory discrimination between long-term-exposed subjects and control subjects was achieved on the basis of these factors. The results were confirmed by a retest investigation one year later.
This study is based on 15 females and 15 males. EEG was recorded with 19 electrodes according to the international 10/20 system against averaged signals picked up from both earlobes. Averaged power spectra and cross-power spectra between adjacent electrodes along the longitudinal and transverse electrode rows (30 local cross spectral and between homologous sites of both hemispheres (8 interhemispheric cross spectral were computed. Data were reduced to 4 frequency bands (Theta, Alpha, Beta1 and Beta2), and finally, mean amplitudes and coherences were computed. During the recordings the subjects had to palpate and recognize three-dimensional objects with their right hand. The obtained spectral parameters were compared with the corresponding values of a baseline activity with eyes closed at rest. The results of statistical evaluations (Wilcoxon tests) were presented in error probability maps. During the task, amplitude decreased in all frequency bands and in all locations. Local coherence increased in the centro-parietal areas indicating an increased coupling between the somatosensory and parietal regions. The increase was most pronounced in the Beta frequency bands and emphasizes the importance of Beta activity during cognitive activation. Concerning gender, differences of local coherence changes were observed in the frontal and temporo-occipital areas. Interhemispheric coherence increase was observed in the centro-parietal regions in both groups but was most pronounced in Beta2 in the female group. These findings suggest the involvement of different brain areas in females and males during palpation and recognition in this tactile task.
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 paper describes some methods of forming sum aggregates in multivariate analysis. These methods are useful for the statistical analysis of investigations with multiple endpoints. In particular, the sum statistics can be applied if differences between two or more populations have to be tested and a factorial structure of the means and covariances can be supposed. For this approach the calculation of principal components has great importance. The central mathematical problem is to construct statistics which permit exact t and F tests, i.e. tests keeping the error of first kind at the prescribed level. The paper is based on the theory of spherical matrix distributions treated extensively in the book by K. T. Fang and Y.-T. Zhang [Generalized multivariate analysis. (1990; Zbl 0724.62054)].
Die Möglichkeit, aus dem Spontan-EEG Aufschlüsse über bestimmte, hirnelektrisch faßbare Denkstrategien zu erhalten, wurde anhand verschiedener kognitiver und kreativer Denkleistungen, sowie am Musikhören demonstriert. Die dazu entwickelte Methode benutzt den Umstand, daß sich der Grad der lokalen Hirnstromproduktion und der elektrischen Verkoppelung verschiedener Rindenregionen bei Denkvorgängen in charakteristischer Weise ändert. Untersucht werden daher die statistisch signifikanten Änderungen (oder Unterschiede) von absoluter Leistung und Kohärenz, die farbkodiert in schematische Hirnkarten eingetragen werden.
Die Ergebnisse an Gruppen von Versuchspersonen lassen Rückschlüsse auf generelle zerebrale Verarbeitungsstrategien selbst während so persönlichkeitsspezifischen Tätigkeiten wie kreativem Denken und Musikhören zu. Dabei ergeben sich Brücken zu psychologischen Testergebnissen und damit zum Grad einer speziellen Ausbildung und der Intelligenz. Untersuchungen mit Extremwertvalidierungen nach Intelligenz- und Kreativitäts-Test-Scores zeigen deutliche Unterschiede zwischen den besten und den schlechtesten Gruppen bei der Lösung einer komplizierten Aufgabe (Visualisierung eines abstrakten Begriffes).
Das EEG verhält sich somit wie deterministisches Chaos, das verschiedene Grade der Organisation aufweisen kann, worin die in ihm enthaltene Information zum Ausdruck kommt. Dabei stellt sich die Frage einer möglichen Funktion des EEG bei der Optimierung von Denkvorgängen.
Often in the social and behavioral sciences, several individual tests of significance are used to determine whether some common or overall hypothesis should be rejected. Thus, it becomes necessary to interpret r significant results out of n tests. Many authors contend that one or more significant results should be interpreted as an overall significant result for the set of tests. The authors of this work suggest that a more appropriate approach would be to use the binomial theorem to compute the probability that r or more Type I errors would occur when all n of the null hypotheses are true, and use this result as the level of overall significance a*. It is shown that in the independent test situation, it is possible to set an action limit r for rejection of the overall hypothesis based on some required overall level of significance a*. In addition, an upper limit is obtained for a* when r significant test results are used to reject a set of n hypotheses when the tests are dependent to an unknown extent.
The differentiation of basic emotions by means of EEG power spectra has been discussed extensively by Machleidt et al. (1989). The present contribution concentrates on the interhemispheric coupling of different EEG-signals as depending on the modulation of these emotions. In the first part the estimation and interpretation of squared coherence spectra is outlined. Results from this technique are presented in the following section. Intention, Aggression and Joy are mainly characterized by an increase of alpha-coherence, whereas a decrease is seen for Anxiety and Sorrow. These effects showed a widespread distribution.
This pilot EEG mapping study was designed to explore thinking processes using complex mental imagery and thought processes. EEG was recorded with 19 electrodes (10/20 system against averaged ear lobe signals) while volunteers (n = 42) performed two separate tasks: visualization of an abstract concept and interpretation of a painting. Average spectral parameters such as amplitude, local and interhemispheric coherences were computed for five frequency bands (theta, alpha, beta 1, 2 and 3). Results indicate that the frontal regions are strongly involved during these tasks as evidenced by coherence changes. Changes are also present in temporal, parietal and occipital regions and are discussed in relation to information processing with the frontal regions considering the different cognitive functions required by the tasks.
To study the problem of consciousness an original structural-functional approach has been applied with the use of possibilities of spectral-coherent EEG analysis in evaluation of human brain functional state together with the specificity of the cerebral coma having local focal belonging. It is revealed that the most informative signs for characteristics of consciousness state are peculiarities of reconstruction of intercentral relations of the electrical brain processes: decrease of mean levels of the EEG coherence at progressive development of coma; staged approach to relative norm at regressive course of comatose state and recovery of consciousness; their stability on the low level at prolonged coma; increase in low or high (above optimum) frequencies band at neighbouring with coma states of consciousness. It may be considered that one of the necessary conditions of normal state of consciousness is preservation of the optimum level of correlation of electrical brain activity alongside with frequency-regional specificity of the EEG coherence spectrum. Any deviation from the optimum is unfavourable condition for normal course of cerebral reactions because of the disturbance of intercentral connections mosaic necessary for their realization.
We analyzed test-retest reliability of EEG coherence during rest and during two cognitive tasks: one verbal, the search for a synonym, and the other consisting of mental mathematical calculations. The experiment was performed twice, with a month's interval between each session. Coherence between all pairwise combinations of the EEG recorded in 15 leads was computed for delta, theta, alpha and beta bands. Comparing the changes observed between sessions for each condition, few significant changes were observed during rest, and the condition which manifests the most changes was calculation. Differences between conditions were observed in the second session in P3-T5, P3-T6, P3-T3, P4-T6, P4-T5, P4-Cz and Cz-T6 delta coherences ordered in a decreasing order from calculation to synonyms to rest. In order to ascertain whether the pattern of coherences across the head in each subject varied in relation to the session and the condition, we computed the correlation coefficients between all coherences values for one condition versus the other condition per band. For all subjects correlation coefficients near unity were observed between conditions in each session. However, correlation coefficients between sessions, even for the same condition, were much lower. We also computed the correlation coefficients for the coherence values between subjects in the same condition separately for each session. Correlation coefficients between subjects were much higher in the second session than in the first one.(ABSTRACT TRUNCATED AT 250 WORDS)
Coherence analysis was applied to the EEG of 19 female participants who had to memorize auditorily presented abstract and concrete nouns. The EEG was recorded from 19 scalp electrodes (10/20 system). Significant differences between both word classes were found only in the beta 1-band (13-18 Hz) whereas the alpha 1-band (8-10 Hz) revealed coherence patterns which were identical for both word classes. These results indicate that the alpha 1-band reflects cognitive processes that were common to both word classes, whereas the beta 1-band seems to be closely related to associative processes and more complex cognitive functions.
In a pilot study, EEG changes during odour administration were evaluated by coherence analysis. Ten normal adults were studied. Simultaneous recordings of 16 EEG channels with, and without, odour administration were stored on magnetic tape for further processing. EEG signals were analysed using a signal analyser. Coherence spectra were calculated between all possible channel pairs on the scalp. The amount of data was reduced by extracting broad band coherence values for five frequency bands: delta (2–3.9 Hz), theta (4–7.9 Hz), alpha 1 (8–9.9 Hz), alpha 2 (10–12.9 Hz), and beta 1 (13–17.9 Hz). Coherence values extracted from the control EEG recordings and those during odour administration were compared to evaluate the presence of any significant differences.
The results demonstrated significant changes in the EEG coherence between the two control recordings (control before and control after) in the theta and beta 1 bands. These frequency bands were therefore excluded from the examination. During odorant stimulation with methyl-cyclopentenolone, the coherence in the delta band decreased in the frontal region, while that in the alpha 1 and alpha 2 bands increased in the temporal region. During odorant stimulation with scatol, the coherence in the delta band decreased in the frontal region, while that in the alpha 1 and alpha 2 bands increased between the longitudinal electrode locations. It was suggested that EEG coherence mapping may provide the basis for the development of an objective test of olfactory function in humans.
The present study was conducted to examine sex differences in interhemispheric EEG coherence in 15 male and 15 female healthy young adults. EEG was recorded during rest and photic stimulation (PS) at 5, 10 and 15 Hz using a linked earlobe reference. Interhemispheric coherence of the resting EEG revealed no significant sex-related differences for any frequency band. In contrast, significant sex-related differences were found in EEG coherence during PS; the females had a significantly higher coherence than the males for F3-F4 and C3-C4 in the frequency band (4.5-5.5 Hz) corresponding to 5 Hz PS. In addition, the changes in interhemispheric coherence from rest to the stimulus condition (i.e. PS-related coherence reactivity) showed sex-related differences at the brain region primarily involved in visual functioning; the females had significantly greater coherence reactivity for O1-O2 in EEG during PS at 5 and 15 Hz. These findings indicate sex-related differences in interhemispheric EEG coherence during PS, and support the well-demonstrated evidence that sex differences exist in the degree of lateralization of cerebral function.
Inter- and intrahemispheric correlation of the EEG activity at rest was computed in two groups of men and women, between 17 and 21 years old, with extreme degrees of spatial ability (SA) evaluated by the Spatial Relations Subtest of the Differential Aptitudes Test (DAT). Interhemispheric (INTERr) and intrahemispheric (INTRAr) EEG correlations were computed by means of Pearson product-moment coefficients for 5 EEG bands after digitally filtering with an FFT. Women showed significantly higher INTERr of alpha 1 between left and right centrals, lower INTRAr between right frontal and right central regions and lower INTRAr within the left than in the right hemisphere. High SA subjects showed lower INTERr between left and right frontal derivations and higher INTRAr between frontal and parietal and between central and parietal regions of both hemispheres. Sex interacted with SA in INTRAr of alpha between right frontal and right temporal regions with high SA women showing lower INTRAr than low SA women and than men. The present results indicate a different inter- and intrahemispheric functional organization in men and women and in subjects with high and low spatial ability.
To investigate the activity of cortical regions in the control of movement, we studied event-related desynchronization/synchronization (ERD/ERS), event-related coherence (ERC), and phase coherence in 29-channel EEGs from 9 subjects performing self-paced movements of the right index finger. Movement preparation and execution produced ERD over the sensorimotor areas at 10 Hz and 20 Hz, followed by ERS. ERD corresponded spatiotemporally to an increase in coherence over the frontocentral areas. For both frequency bands, ERD began over the left sensorimotor areas and became bilateral at the time of movement onset. The coherence increase with frontal areas began in the left central areas and became symmetrical after EMG onset. The ERD and coherence increase was longer at 10 Hz than at 20 Hz. Phase coherence at 10 Hz showed a lead of anterior regions to posterior regions throughout the time period, and at 20 Hz showed a tendency toward zero phase delay corresponding with the movement. EEG desynchronization parallels functional coupling over sensorimotor and frontal areas. Event-related coherence and phase coherence findings implicate the frontal lobes in control of movement planning and execution. The involvement of different frequency bands with different timings may represent parallel changes in the cortical network.
In this study the sensitivity of instantaneous EEG coherence for the description of the processual evolution of thinking processes is investigated. The adaptive estimation approach presented allows the calculation of the coherence function with high time and frequency resolution. On this basis the detection of time intervals with high synchronization phenomena is possible. The strength of coupling between different EEG channels may therefore be measured even for very short mental activities. The inclusion of the time component enables the calculation of very sensitive coherence parameters, such as the maximal coherence value or the length of time intervals with high synchronization during information processing. Based on these dynamic examinations, conceptual and imaginal representations are distinguishable for elementary cognitive processes.