Dyslexia is a common neurobehavioral disorder with reported prevalence rates of 5- 10%, but the exact biological mechanisms underlying the abnormalities observed in dyslexics remain unclarified. Researchers have shown that many dyslexics have difficulty processing basic sensory information from at least one modality, such as auditory or visual stimuli. However, the study of cross-modal (simultaneous sensory input from two modalities, such as auditory and visual stimuli) sensory processing in dyslexia remains relatively unexplored. Our proposed research is intended to fill this knowledge gap through behavioral, anatomical, and functional magnetic resonance imaging (fMRI) brain-mapping studies of cross-modal sensory processing in a unique, well-studied group of dyslexics known as the Orton Cohort. Our theory concerns the interaction between a known cortical language network and a multisensory area in the left posterior superior temporal sulcus (PSTS). When performing a cross-modal task, the language circuit determines if the two stimuli match. Matching information is sent to the PSTS and bound into a unified percept, while nonmatching information is sent to the PSTS but not bound. In dyslexia, we believe that the language circuit is unable to properly determine whether the cross-modal stimulus pairs match so more cross-modal stimuli are bound in the PSTS by default. To test these hypotheses, Specific Aims were designed to collect fMRI data and behavioral measures on control subjects and dyslexic subjects during the performance of a cross-modal phoneme-grapheme matching task. Volumetric gray matter measurements in key regions are also made, to assess the possibility of an underlying anatomical deficit. Our project fits the R21 research mission in the following ways: the study of cross-modal sensory integration in dyslexia is a novel, but nonetheless logically appropriate, avenue of investigation and has the potential to provide groundbreaking insights into the neural mechanisms responsible for this disorder. This preliminary project is a necessary first step along a course of many potential future investigations in dyslexia, such as genetic linkage studies, remediation studies, and more focused studies into which aspect of cross-modal processing is deficient. In addition, the identification of cross-modal processing abnormalities would validate and allow further optimization of training methods employed to treat dyslexia.

R21NS044149

2004-06-01

2007-05-31