The neglected role of the right hemisphere in spatial representation of words for reading

Abstract

Background: Previous studies have indicated that focal brain damage can result in different types of “neglect dyslexia” (reading errors specific to the side of printed material contralateral to the side of brain damage).Aims: To identify the sites of lesions (or dysfunctional brain tissue) responsible for distinct types of neglect dyslexia, to inform a functional neuroanatomical model of brain regions involved in early stages of reading.Methods & Procedures: A battery of tests of hemispatial neglect and reading designed to distinguish neglect dyslexia in different reference frames (viewer-centred, stimulus-centred, and object-centred) was administered to 95 patients within 48 hours of onset of nondominant hemisphere stroke. Magnetic resonance diffusion and perfusion imaging was obtained on the same day as testing. Associations between each type of neglect dyslexia and areas of hypoperfusion and/or infarct were evaluated using chi-squared tests.Outcomes & Results: Viewer-centred neglect dyslexia was associated with hypoperfusion and/or infarct in right angular and supramarginal gyri and visual association cortex (“dorsal stream”). Stimulus-centred neglect dyslexia was associated with hypoperfusion and/or infarct of right superior temporal cortex (“ventral stream”). Object-centred neglect dyslexia was observed only with hypoperfusion and/or infarct of non-dominant superior temporal cortex in left-handed individuals.Conclusions: The identified associations provide evidence that different regions of cortex are critical for spatial attention to, or processing of, representations of words with distinct coordinate frames in the reading task.