Affiliations: Department of Neurology, Johns Hopkins School of
Medicine, Baltimore, MD, USA | Stanford University School of Medicine, CA, USA | Department of Neurology, The Johns Hopkins Hospital,
Baltimore, MD, USA | Department of Neurology, University of Toronto,
Toronto, ON, Canada
Note: [] Corresponding author: Amitabh Gupta, Toronto Western Hospital,
Morton and Gloria Shulman Movement Disorder Centre, 399 Bathurst Street,
McLaughlin 7-418; Toronto, ON, Canada M5T 2S8. Tel.: +1 416 603 6422; Fax: +1
416 603 5004; E-mail: amigupta@uhnres.utoronto.ca
Abstract: Spatial processing is lateralized: the right hemisphere is optimized
for perceiving global aspects of space ("seeing the forest"), while the left
hemisphere specializes in perceiving local aspects of space ("seeing the
trees"). However, less is known about how the information is shared across the
hemispheres and which areas within the corpus callosum are required for
transferring and integrating visuospatial information. Here, we report a 60
year old woman with a mass lesion in the splenium of the corpus callosum who
demonstrated visuospatial processing deficits that were out-of-proportion to
the rest of her neurological examination. Remarkably, in the Rey-Osterrieth
Complex figure task, she copied with her left hand the outlines of the figure
(global aspects), whereas with her right hand she drew the details of that
figure (local aspects). While hemispheric lesions have demonstrated single
dissociations of spatial processing, these results indicate that a lesion in
the corpus callosum can produce a double dissociation for high-level spatial
tasks, as local and global spatial perception are further dissociated with
handedness. Interestingly, as little as the posterior third of the corpus
callosum is required for proper visuospatial information transfer and
integration, which provides important insight into the interhemispheric
functional anatomy that underlies visuospatial perception.
Keywords: Visuospatial processing, double dissociation, corpus callosum
