Cerebral Cortex Advance Access published online on October 8, 2008
Cerebral Cortex, doi:10.1093/cercor/bhn173
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Functional Relevance of Interindividual Differences in Temporal Lobe Callosal Pathways: A DTI Tractography Study
1 Department of Biological and Medical Psychology, Cognitive Neuroscience Group, University of Bergen, N-5009 Bergen, Norway, 2 Department of Radiology, Haukeland University Hospital, N-5201 Bergen, Norway, 3 Department of Physics and Technology, University of Bergen, N-5007 Bergen, Norway, 4 Clinical Engineering Department, Haukeland University Hospital and University of Bergen, N-5201, Bergen, Norway, 5 Division of Psychiatry, Haukeland University Hospital, N-5021 Bergen, Norway
Address correspondence to René Westerhausen, Cognitive Neuroscience Group, Department of Biological and Medical Psychology, University of Bergen, Jonas Lies vei 91, N-5009 Bergen, Norway. Email: rene.westerhausen{at}psybp.uib.no.
The midsagittal corpus callosum is topographically organized, that is, with regard to their cortical origin several subtracts can be distinguished within the corpus callosum that belong to specific functional brain networks. Recent diffusion tensor tractography studies have also revealed remarkable interindividual differences in the size and exact localization of these tracts. To examine the functional relevance of interindividual variability in callosal tracts, 17 right-handed male participants underwent structural and diffusion tensor magnetic resonance imaging. Probabilistic tractography was carried out to identify the callosal subregions that interconnect left and right temporal lobe auditory processing areas, and the midsagittal size of this tract was seen as indicator of the (anatomical) strength of this connection. Auditory information transfer was assessed applying an auditory speech perception task with dichotic presentations of consonant–vowel syllables (e.g., /ba-ga/). The frequency of correct left ear reports in this task served as a functional measure of interhemispheric transfer. Statistical analysis showed that a stronger anatomical connection between the superior temporal lobe areas supports a better information transfer. This specific structure–function association in the auditory modality supports the general notion that interindividual differences in callosal topography possess functional relevance.
Key Words: corpus callosum • dichotic listening • diffusion-tensor imaging • inter-individual differences • speech perception