Callosal degeneration topographically correlated with cognitive function in amnestic mild cognitive impairment and alzheimer's disease dementia

Abstract

Degeneration of the corpus callosum (CC) is evident in the pathogenesis of Alzheimer's disease (AD). However, the correlation of microstructural damage in the CC on the cognitive performance of patients with amnestic mild cognitive impairment (aMCI) and AD dementia is undetermined. We enrolled 26 normal controls, 24 patients with AD dementia, and 40 single-domain aMCI patients with at least grade 1 hippocampal atrophy and isolated memory impairment. Diffusion tensor imaging (DTI) with fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (DA), and radial diffusivity (DR) were measured. The entire CC was parcellated based on fiber trajectories to specific cortical Brodmann areas using a probabilistic tractography method. The relationship between the DTI measures in the subregions of the CC and cognitive performance was examined. Although the callosal degeneration in the patients with aMCI was less extended than in the patients with AD dementia, degeneration was already exhibited in several subregions of the CC at the aMCI stage. Scores of various neuropsychological tests were correlated to the severity of microstructural changes in the subregional CC connecting to functionally corresponding cortical regions. Our results confirm that CC degeneration is noticeable as early as the aMCI stage of AD and the disconnection of the CC subregional fibers to the corresponding Brodmann areas has an apparent impact on the related cognitive performance.

Insights into White Matter Damage in Alzheimer's Disease: From Postmortem to in vivo Diffusion Tensor MRI Studies

“…A prominent involvement of temporoparietal regions and, to a lesser extent, the frontal lobes has been detected by both region of interest [35,36,37,38] and voxel-based DT MRI studies [39,40,41,42]. Tractography studies in AD showed the presence of diffusion abnormalities in the major limbic tracts, such as the fornix [43,44] and cingulum [45,46], and corticocortical association tracts, such as the corpus callosum (CC) [43,45,47], uncinate [43,45,48], inferior fronto-occipital [43,49], superior longitudinal [43] and inferior longitudinal [43] fasciculi. An increased radial diffusivity is commonly found in AD involving temporal, frontal and parietal regions [42,50] while less consistent results are reported for axial diffusivity [40,41,51,52].…”

Callosal damage and cognitive deficits in chronic carbon monoxide intoxication: A diffusion tensor imaging study

“…All image data analyses and parcellations of the CC were performed as previously described in detail [18].…”

“…To reduce eddy current distortions and motion artifacts, each diffusion-weighted image was registered to the non-diffusion weighted image by an affine registration approach that was supplied in FMRIB's Linear Image Registration Tool. We then used the Brain Extraction Tool to strip the skull from the non-diffusion weighted image and from the corresponding T1-weighted image of each participant to remove non-brain tissue and background noise from the images, ensuring the accuracy of cross-modality image registration [17,18].…”

“…A probabilistic tractography was performed to parcellate the entire three-dimensional human CC into different subregions based on connection profiles according to previous detailed literature [18,20,21]. The probability distribution function of the principal fiber direction was calculated in each voxel using a Bayesian approach involving the use of sampling techniques for crossing fibers (BEDPOSTX; part of FSL).…”

“…To determine the target masks of the fiber tractography, the cortical probability image (HarvardOxford-cortmaxprob-thr25-2 mm, provided by the Harvard-Oxford Cortical Structural Atlas) was used to parcellate the whole cortex into seven cortical regions, namely, the prefrontal, the premotor and supplementary motor, the primary motor, the primary sensory, the parietal, the occipital, and the temporal cortices. The definitions used for the seven cortical regions followed those given by previous studies [18,23,24], and detailed definitions of the regions are listed in Supplementary Table A. After probabilistic tracking, the number of samples that passed through each cortical target region was recorded and a probability of the connection from the seed region to each cortical region was calculated as a proportion of the total number of samples (5000 samples). Hard segmentation of the entire CC was performed by classification of the seed region according to the highest probability of connection to the corresponding cortical target regions.…”