Pii: S1388-2457(01)00545-4

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 re ̄ects the encoding of new information into working memory. The aim of the present study was to investigate whether the processing de®cits 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 re ̄ect the effort during the encoding process. q 2001 Elsevier Science Ireland Ltd. All rights reserved.