Cerebral Cortex Advance Access originally published online on August 18, 2004
Cerebral Cortex 2005 15(5):507-513; doi:10.1093/cercor/bhh150
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Cerebral Cortex V 15 N 5 © Oxford University Press 2004; all rights reserved
Abnormal Response Recovery in the Right Somatosensory Cortex of Dyslexic Adults
1 Brain Research Unit, Low Temperature Laboratory, Helsinki University of Technology, FIN-02015 HUT, Espoo, Finland and 2 Department of Clinical Neurophysiology, Helsinki University Central Hospital, FIN-00290 Helsinki, Finland
Correspondence to: Hanna Renvall, MD PhD, Brain Research Unit, Low Temperature Laboratory, Helsinki University of Technology, P.O. Box 2200, FIN-02015 HUT, Espoo, Finland. Email: hanna{at}neuro.hut.fi.
Somatosensory evoked fields (SEFs) to repetitive tactile stimuli were recorded from eight dyslexic and eight normal-reading adults. Three successive stimuli, produced by diaphragms driven by compressed air, were delivered to thumb, index finger and thumb in sequence, with stimulus-onset asynchronies (SOAs) of 100 and 200 ms in different runs. Both hands were stimulated alternatingly with an intertrain interval of 1 s, and the responses were recorded with a whole-scalp neuromagnetometer. Whereas the primary somatosensory cortex responses to the first stimuli of the trains did not differ between dyslexics and controls, responses to the second stimuli (and the ratios of second to first responses) were significantly smaller in dyslexic than in control subjects in the right hemisphere (differences 41 and 28% for response amplitudes at the 100 and 200 ms SOAs). The results agree with the proposed pansensory nature of temporal processing deficits in dyslexia, specifically demonstrating abnormal response recovery in the right somatosensory cortex.
Key Words: dyslexia • magnetoencephalography • MEG • somatosensory • tactile