Relationship between regional corpus callous atrophy and paced auditory serial addition test in multiple sclerosis

Abstract

Introduction: The Paced Auditory Serial Addition Test (PASAT) is a sensitive measure of cognitive dysfunction in Multiple Sclerosis (MS). Using functional imaging, PASAT performance has been shown to be associated with activation of bilateral cortical regions within the frontal, parietal and temporal cortices. The corpus callosum (CC) serve topographically organised inter-hemispheric interactions between the cortical regions. Here we test the hypothesis that regional volume loss within CC may impair PASAT performance. Methods: We administered PASAT to 44 women with relapsing remitting MS and mild neurological disability (median EDSS=1.5), who underwent a structural MRI scan on a 1.5T magnet. Post-processing analysis was performed with the FreeSurfer software. CC was parcellated into five regions of same length; the volume of each region was normalised to the total brain volume and used for statistical analysis. Results: Mean (+/- standard deviation) PASAT score was 37.1 (+/-12.6). Multivariate analysis showed a significant effect of the normalised volume of the CC posterior region on PASAT performance, i.e., higher PASAT performance was associated with higher normalised volume of the CC posterior region. No relationship was found between PASAT scores and normalised volumes of other CC regions or the total CC volume. Discussion: Our results show a localised, specific association between PASAT performance and regional loss in the posterior part of CC. Functional anatomy of interhemispheric cortical connections revelas an antero-posterior topography within CC, with the the posterior regions containing fibres connecting temporal and parietal cortices. Damage to this portion of CC may impair auditory information processing speed and flexibility, as well as calculation ability required for PASAT performance.