Biomedical subjects

D Röhm

Publications and source records attributed to D Röhm.

7 recordsLinked to original sources

PubMed2001

The role of theta and alpha oscillations for language comprehension in the human electroencephalogram.

The hypothesis is tested, whether increasing language processing demands draw on the capacity of working memory thereby leading to an increase in theta band power. Previous research has shown that theta reflects working memory whereas upper alpha semantic memory demands. Sentences were presented in four chunks in a reading and a semantic task. In the latter, subjects had to find a superordinate concept to a noun presented in the third chunk. The data show an increase in theta during sentence processing which was significantly smaller in the semantic task. In contrast, the upper alpha band exhibited a significantly larger change in band power during the semantic task and that time window in which subjects searched for the superordinate concept. Thus, we conclude that semantic processing does not draw selectively on the capacity of working memory and that different linguistic processes have no direct influence on theta oscillations.

Adult↗

PubMed2001

Episodic retrieval is reflected by a process specific increase in human electroencephalographic theta activity.

Is an increase in theta during retrieval due (primarily) to the access of a stored code or to more general processes? The electroencephalogram was recorded while subjects performed a recognition task with pictures. According to the event-related desynchronization/synchronization method, the percentage of band power changes was calculated during encoding and retrieval for a theta and three alpha bands. Significant results were obtained (with minor exceptions) only in the theta band. The increase in theta was significantly larger during retrieval than during encoding but did not differ significantly between new and successfully retrieved old pictures. Because a memory trace is lacking for new pictures, the increase in theta during retrieval reflects primarily general processing demands of a complex episodic memory system.

Adult↗

PubMed2001

Theta synchronization during episodic retrieval: neural correlates of conscious awareness.

The neural correlates of conscious awareness during successful memory retrieval were examined. In a recognition test, subjects indicated whether they consciously recalled the event in which a word was earlier presented (Remembering), or whether they recognized it on the basis that it was familiar in the absence of recollection (Knowing). An early EEG synchronization in the theta band predicted knowing, and a later remembering. Moreover, early and late event-related potentials were also found to predict knowing and remembering, respectively. The results indicate that the temporal dynamics of theta synchronization are related to the particular conscious experiences associated with memory retrieval.

Adult↗

PubMed2001

Alpha and beta band power changes in normal and dyslexic children.

OBJECTIVE: Previous research with healthy subjects suggests that the lower alpha band reflects attentional whereas the upper alpha band semantic processes. The aim of the present study was to investigate whether dyslexics show deficits in attentional control and/or semantic encoding. METHOD: The EEG was recorded while subjects were reading numbers, words and pseudowords and analyzed in a lower and upper alpha and two beta bands (spanning a range of about 8--16 Hz). A phasic response is measured in terms of a decrease in event related band power during reading with respect to a reference interval. Tonic power is measured in terms of (log) band power during a reference interval. RESULTS: In the lower alpha band dyslexics show an increased phasic response to words and pseudowords at right hemispheric sites but a lack to respond to words at O1. The upper alpha band exhibits a highly selective phasic response to words at left frontal sites but for controls only, whereas dyslexics show a general increase in tonic upper alpha power. Whereas the low frequency beta band (beta-1a) exhibits a rather diffuse pattern, a highly selective finding was obtained for the beta-1b band. CONCLUSIONS: Dyslexics have a lack of attentional control during the encoding of words at left occipital sites and a lack of a selective topographic activation pattern during the semantic encoding of words. Because only in controls reading of words is associated with a strong beta-1b desynchronization at those recording sites which correspond to Broca's area (FC5) and the angular gyrus (CP5, P3), we may conclude that this frequency band reflects the graphemicphonetic encoding of words.

Alpha Rhythm↗

PubMed2001

Theta band power changes in normal and dyslexic children.

OBJECTIVE: Tonic and phasic (event-related) theta band power changes were analyzed in a sample of 8 dyslexic and 8 control children. Previous research with healthy subjects suggests that electroencephalograph (EEG) theta activity reflects the encoding of new information into working memory. The aim of the present study was to investigate whether the processing deficits of dyslexics are related to a reduced phasic theta response during reading. METHOD: The EEG was recorded while subjects were reading numbers, words and pseudowords and analyzed in a lower and upper theta band (4--8 Hz). A phasic response is measured in terms of an increase in event related band power during reading with respect to a reference interval. Tonic power is measured in terms of (log) band power during a reference interval. RESULTS: Large group differences in tonic and phasic lower theta were found for occipital sites where dyslexics show a complete lack of pseudoword processing. For words, only controls show a highly selective left hemispheric processing advantage. CONCLUSIONS: Dyslexics have a lack to encode pseudowords in visual working memory with a concomitant lack of frontal processing selectivity. The upper theta band shows a different pattern of results which can be best interpreted to reflect the effort during the encoding process.

Child↗

PubMed2000

Simultaneous desynchronization and synchronization of different alpha responses in the human electroencephalograph: a neglected paradox?

This study aims to resolve a paradox. Experiments measuring alpha band power report an event related decrease (desynchronization) in alpha activity, whereas those measuring evoked alpha report synchronization. During a recognition memory task with human subjects, we measured the evoked (phase locked) and induced (not phase locked) alpha response. The findings reveal that evoked alpha is due to a transient phase locking (at about 100-200 ms poststimulus) of three alpha sub-bands which can be observed only at parieto-occipital sites. In contrast, induced alpha shows a widespread pattern of desynchronization at most recording sites. Thus, opposite alpha responses occur within similar time windows. Evoked alpha synchronization may reflect cortical inhibition which serves to increase the signal to noise ratio for activation processes following immediately later.

Adolescent↗

PubMed2000

The time locked theta response reflects interindividual differences in human memory performance.

Recent research indicates that an increase in theta band power is related to episodic memory performance. In this study with human subjects, the evoked (time locked) and induced (not time locked) theta response is analyzed in a recognition task. The results show a strong evoked theta response during an early retrieval period of up to 400 ms. Only for good memory performers theta is strictly time locked, indicating that theta peaks appear in preferred time windows after a target is presented. This effect--which coincides with a large P3--suggests that good performance requires a strict timing of different processing stages that correspond to cycles of theta activity.

Adult↗