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.


METHODS
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.
Klimesch
W
W
Department of Physiological Psychology, Institute of Psychology, Hellbrunnerstrasse 34A-5020, Salzburg, Austria. wolfgang.klimesch@sbg.ac.at
Doppelmayr
M
M
Wimmer
H
H
Schwaiger
J
J
Röhm
D
D
Gruber
W
W
Hutzler
F
F
D002648:Child; D004410:Dyslexia / Q000503:physiopathology* / Q000523:psychology; D004569:Electroencephalography; D005071:Evoked Potentials / Q000502:physiology; D006801:Humans; D008297:Male; D011597:Psychomotor Performance / Q000502:physiology; D011932:Reading; D013826:Theta Rhythm / Q000523:psychology*