Theta synchronization and alpha desynchronization in a memory task.

In the present study, we examined the hypothesis that episodic encoding and retrieval processes are primarily reflected by a task-related increase in theta power. Individuals performed a recognition task with a total of 192 words. The electroencephalogram was recorded during the study and recognition phase. The results show that only those words that were later correctly recognized produced a significant increase in theta power during encoding. During the actual recognition processes too, a significant theta synchronization (increase in band power) was found for correctly remembered words only. In contrast to the theta band, remembered and not remembered words revealed a complex pattern of desynchronization in the lower and upper alpha band that was different during encoding and recognition.

Event-related desynchronization (ERD) and the Dm effect: does alpha desynchronization during encoding predict later recall performance?

Based on previous research which has shown that event-related desynchronization (ERD) in the lower and upper alpha band reflects attentional and semantic processing respectively, the present study examines the hypothesis whether event-related shifts in the two alpha bands are capable of predicting later recall performance. In an incidental memory paradigm, subjects first had to judge the category membership for a set of 96 words. Later, without prior warning, subjects were asked to recall the words. The results show that for good performers, the extent of ERD in the lower alpha band during the semantic encoding for words is significantly larger for remembered as compared to not remembered words, whereas for bad performers the ERD in the upper alpha band is significantly more pronounced. This type of Dm effect is particularly strong over parietal recording sites in both hemispheres. In referring to the proposed interpretation of the lower and upper alpha band, the present findings seem to indicate that in contrast to good performers, bad performers are less attentive or alert during encoding. Event-related potentials (ERPs) also yielded significant Dm effects at parietal recording sites.

Alpha frequency, reaction time, and the speed of processing information.

Several experiments indicate that alpha frequency is significantly correlated with the speed of information processing, as measured by reaction times. These data imply that alpha frequency is a timing mechanism for cognitive processes. However, this interpretation contradicts the well-accepted view that there is no single alpha rhythm, but instead an entire population of different alpha oscillations. We present arguments and report data in the attempt to demonstrate that this paradox can be resolved if different states of alpha oscillations are distinguished. The results of the present study show that during a state of desynchronization, task-related shifts in alpha frequency are not "real" because they are not related to reaction times. Instead, they most likely reflect power changes in different frequency bands.

Clinical case report: opiate antagonist and event-related desynchronization in 2 autistic boys.

Event-related desynchronization and visual orientational behavior were examined in 2 autistic boys to determine if blockade of endogenous opioid activity facilitates cognitive processing at a cortical level. Before naltrexone, the boys showed no selective alpha blocking during exposure to either mother's pictures or white light. Unlike normals, they exhibited strong alpha band enhancement at temporocentral recording sites. Two hours after administering 0.5 mg/kg naltrexone, mother-as well as light-related alpha blocking appeared at occipital, occipitotemporal, and prefrontal sites. These effects were gone 24 h after dosing in one child, but persisted in the other. A parallel increase in visual pursuit in a social context was observed. These results affirm that autistic gaze aversion can be caused by excessive opioid activity interfering with corticothalamocortical processing of visual stimuli.

Episodic and semantic memory: an analysis in the EEG theta and alpha band.

This study examines the hypothesis that in contrast to semantic memory processes that are assumed to be reflected primarily within the alpha band, episodic memory processes are related to activity within the theta band. EEG signals were recorded from subjects as they performed a semantic congruency and an episodic recognition task. In the semantic task, subjects had to judge whether or not sequentially presented concept-feature pairs (such as "eagle-claws" or "pea-huge") are semantically congruent. In the episodic task, which followed the semantic task without prior warning, the same word pairs were presented together with new distractors (generated by repairing known concept-feature pairs). Here, subjects judged whether or not a particular concept-feature pair was already presented during the semantic task. EEG data were analyzed using event-related desynchronization (ERD) as a measure for the amount of event-related changes in band power in the theta band and in the upper and lower alpha bands. The alpha band was determined individually, using the alpha peak frequency during the resting period as the cut-off point to separate the lower from the upper alpha band. The results, which are based on those identical word pairs that demanded a yes response in both tasks, showed that semantic memory processes are indeed primarily reflected in the upper alpha band whereas episodic memory processes are reflected in the theta band. The possible relationship between hippocampal theta activity and the encoding of episodic information is discussed.

Alpha frequency, cognitive load and memory performance.

EEG-signals were recorded from subjects as they performed a modified version of Schneider's and Shiffrin's memory search paradigm. The hypothesis was tested whether individual (centre of gravity) alpha frequency, termed IAF, is related to memory performance and/or attentional demands. The results show that memory performance exerts the strongest effect on IAF. As compared to a resting period, the difference in IAF between age-matched good and bad memory performers reached a maximum when subjects were actually retrieving information from their memory. During retrieval, the IAF of good performers is 1.25 Hz higher than for bad performers. Attentional and task demands also tend to reduce IAF, but as compared to memory performance-to a much lesser degree. The results of amplitude analyses demonstrate further that during retrieval, alpha desynchronization is more pronounced for bad performers than for good performers. Taken together, the results indicate that a decrease in IAF is always related to a drop in performance.

[Event-related desynchronization and the selection of an alpha-frequency band for quantifying cortical pre- and poststimulus activation]. / Ereignisbezogene Desynchronisation und die Wahl des Alpha-Frequenzbandes zur Quantifizierung kortikaler Prä- und Poststimulus-Aktivierung.

The amount of event-related decrease of increase in alpha-band power is termed "Event-Related Desynchronization" or ERD. In this study, ERD is used as an index of cortical activation, which not only can be applied to monitor poststimulus but prestimulus processes as well. Usually, ERD is analyzed within a fixed range of alpha-frequency, typically within a range of 8-12 Hz. alpha-frequency, however, shows a considerable between subject variation, even in a sample of subjects with comparable age. The purpose of this study, thus is to show as to how the range of alpha-frequency affects the calculation of ERD. Two different methodological approaches were compared. First, ERD was calculated within a fixed range of 8-12 Hz. Second, ERD was calculated within an individual range, which was adjusted to the individually determined alpha-frequency of each subject. A sample of ten right handed subjects participated in an episodic memory experiment, in which target words, shown in a earlier session of the experiment, were to be identified. A time span of 375 ms preceding and following the presentation of a word was defined as the "pre-" and "poststimulus" interval. EEG-signals were recorded unipolarly from 29 leads. The results show a rather localized increase of ERD in the poststimulus interval. In the prestimulus interval on the other hand, the average magnitude of ERD is much lower and the topographical distribution less localized. Most importantly, however, when comparing the two methods of analyzing ERD, those ERD-values calculated within an individually determined alpha-band, are superior in order to differentiate between the pre- and poststimulus interval.

Event-related desynchronization, ERD-mapping and hemispheric differences for words and numbers.

Event-related desynchronization (ERD) is the amount of event-related decrease in alpha band power. In applying ERD as an index of cortical activation, the way in which attention and expectancy affect hemispheric differences for words and numbers was investigated. Subjects, 12 right-handed males, had to perform a semantic and a numerical classification task under two different counterbalanced expectancy conditions. Whereas under the high expectancy condition words and numbers were presented blockwise, they were presented randomly under the low expectancy condition. In the semantic task subjects had to indicate the category to which a word belonged; in the numerical task they had to judge whether a number was odd or even. Because 48 words and numbers were used in both expectancy conditions, each subject had to perform a total of 192 trials, practice trials not included. During each of the 192 trials, EEG-signals were recorded from 29 electrodes and analyzed in two frequency bands (6-10 Hz and 9-13 Hz). The data, which were also presented in the form of maps, were subjected to a 6-factorial ANOVA. The results reveal a complex pattern of interactions between the two frequency bands, expectancy conditions, stimulus types and the recording sites. The most important results concern the influence of expectancy. A consistent left hemispheric advantage could be observed under the high expectancy condition and in the lower alpha band only. This and other results seem to indicate that the lower alpha band is more sensitive to reflect expectancy and attentional processes.

The value of P300 in the diagnosis of cognitive impairment in stroke.

The latency of the P300 and the simple reaction time (RT) generated by visual stimuli were investigated in a group of 43 healthy normals and in 24 stroke patients. The stroke patients were in a chronic phase of their disease. Twelve patients were without cognitive deficit, while 12 showed the symptoms of dementia. In the normals, P300 and RT showed a positive correlation with age. In comparing 12 age-matched normals with stroke patients with and without dementia, a similar latency of the P300 was found in the normals (347 msec) and in the stroke patients without dementia (349 msec). The patients with cognitive impairment showed a significant increase in their latency (434 msec). The RT was significantly different in the normals (421 msec) and stroke patients without dementia (533 msec) as well as in the stroke patients with dementia (663 msec). A significant correlation between the P300 and the RT was found.

[Effectiveness of a patient-centered psychosomatic consultation service. Report of a catamnestic study]. / Zur Wirksamkeit des patientenzentrierten psychosomatischen Konsiliardienstes. Bericht über eine katamnestische Untersuchung.

After a short review of the latest scientific publications on psychosomatic consultation activity the results of an empirical study of the consultant service in the Department of Psychotherapy and Psychosomatic Medicine at the Frankfurt University Medical Center are presented. Patient documentations and data from a retrospective investigation were analysed in order to trace the effectivity of psychosomatic consultation activities. To document the various dimensions of the consultative process and their interdependence different groups of patients were derived by means of cluster analysis. The results are in many aspects encouraging for psychosomatic consultative practice, as they show that even few consultations can have an important influence on the patient's further development.

[Visual evoked potentials and hemispheric differences: on the functional significance of homologous regions]. / Visuell evozierte Potentiale und Hemisphärendifferenzen: Zur funktionellen Bedeutung homologer Regionen.

A total of 18 right handed subjects participated in an experiment, in which visually evoked potentials were recorded from four scalp electrodes (01, 02 and P3, P4) when words or flashes of diffuse light were presented as stimuli. The evoked potentials were subdivided into three components, an early component (Komp1, 0-150 ms) and two late components (Komp2, 150-300 and Komp3, 300-450 ms). For each of these components and for each subject, correlations were computed between different recording sites. The results show that homologous correlations (01:02, P3:P4) yield values, which are significantly higher than the values of the intra- (01:P3, 02:P4) and diagonal interhemispheric (01:P4, 02:P3) correlations. This result, which holds true for all of the three components in a similar way, is independent from the type of presented stimuli. In contrast to homologous correlations, intra- and diagonal interhemispheric correlations do vary as a function of stimulus type and different components as well. Here, the results show that the degree of correlation between different recording sites is positively related to the degree of cognitive load: with increasing cognitive load, the degree of synchronous neural activity increases. Homologous correlations are independent from the type of stimuli (words and pictures) and from the type of VEP-components (Komp1, 2, and 3) as well. Thus, it can be concluded that homologous correlations reflect attentional rather then cognitive processes.