HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Helenius, P. Articles by Connolly, J. F. Search for Related Content PubMed PubMed Citation Articles by Helenius, P. Articles by Connolly, J. F.

Semantic Cortical Activation in Dyslexic Readers

^a Helsinki University of Technology
^b University of Helsinki
^c Dalhousie University

The combined temporal and spatial resolution of MEG (magnetoencephalography) was used to study whether the same brain areas are similarly engaged in reading comprehension in normal and developmentally dyslexic adults. To extract a semantically sensitive stage of brain activation we manipulated the appropriateness of sentence-ending words to the preceding sentence context. Sentences, presented visually one word at a time, either ended with a word that was (1) expected, (2) semantically appropriate but unexpected, (3) semantically anomalous but sharing the initial letters with the expected word, or (4) both semantically and orthographically inappropriate to the sentence context. In both subject groups all but the highly expected sentence endings evoked strong cortical responses, localized most consistently in the left superior temporal cortex, although additional sources were occasionally found in more posterior parietal and temporal areas and in the right hemisphere. Thus, no significant differences were found in the spatial distribution of brain areas involved in semantic processing between fluent and dyslexic readers. However, both timing and strength of activation clearly differed between the two groups. First, activation sensitivity to word meaning within a sentence context began about 100 msec later in dyslexic than in control subjects. This is likely to result from affected presemantic processing stages in dyslexic readers. Second, the neural responses were significantly weaker in dyslexic than in control subjects, indicating involvement of a smaller or less-synchronous neural population in reading comprehension. Third, in contrast to control subjects, the dyslexic readers showed significantly weaker activation to semantically inappropriate words that began with the same letters as the most expected word than to both orthographically and semantically inappropriate sentence-ending words. Thus, word recognition by the dyslexic group seemed to be qualitatively different: Whereas control subjects perceived words as wholes, dyslexic subjects may have relied on sublexical word recognition and occasionally mistook a correctly beginning word for the one they had expected.

This article has been cited by other articles:

				H. Denhart Deconstructing Barriers: Perceptions of Students Labeled With Learning Disabilities in Higher Education J Learn Disabil, November 1, 2008; 41(6): 483 - 497. [Abstract] [PDF]

				S.L. Rimrodt, A.M. Clements-Stephens, K.R. Pugh, S.M. Courtney, P. Gaur, J.J. Pekar, and L.E. Cutting Functional MRI of Sentence Comprehension in Children with Dyslexia: Beyond Word Recognition Cereb Cortex, June 4, 2008; (2008) bhn092v2. [Abstract] [Full Text] [PDF]

				L. Pylkkanen, R. Llinas, and G. L. Murphy The Representation of Polysemy: MEG Evidence J. Cogn. Neurosci., January 1, 2006; 18(1): 97 - 109. [Abstract] [Full Text] [PDF]

				A. Proverbio, L. Vecchi, and A. Zani From Orthography to Phonetics: ERP Measures of Grapheme-to-Phoneme Conversion Mechanisms in Reading J. Cogn. Neurosci., February 1, 2004; 16(2): 301 - 317. [Abstract] [Full Text] [PDF]

				P. Helenius, R. Salmelin, U. Richardson, S. Leinonen, and H. Lyytinen Abnormal Auditory Cortical Activation in Dyslexia 100 msec after Speech Onset J. Cogn. Neurosci., May 1, 2002; 14(4): 603 - 617. [Abstract] [Full Text] [PDF]

				P. Helenius, R. Salmelin, E. Service, J. F. Connolly, S. Leinonen, and H. Lyytinen Cortical Activation during Spoken-Word Segmentation in Nonreading-Impaired and Dyslexic Adults J. Neurosci., April 1, 2002; 22(7): 2936 - 2944. [Abstract] [Full Text] [PDF]

				C. von Karolyi Visual-Spatial Strength in Dyslexia: Rapid Discrimination of Impossible Figures J Learn Disabil, July 1, 2001; 34(4): 380 - 391. [Abstract] [PDF]