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Editors Selection IGR 16-4
Basic Research: Changes in cortical grey matter
Comment by Yeni Yucel on:
24675 Changes in cortical grey matter density associated with long-standing retinal visual field defects, Boucard CC; Hernowo AT; Maguire RP et al., Brain: a journal of neurology, 2009; 132:Pt 7 1898-1906
Using images from 3.0 Tesla MRI and voxel-based morphometry, Boucard et al. (1404) report grey density reduction in the primary visual cortex in patients with advanced glaucoma and age-related macular degeneration compared to control group. The results of this study support previous studies demonstrating neurodegeneration in experimental monkey and human glaucoma. Homogeneity of groups being studied is particularly important when using voxel based morphometry, and specific information regarding the clinical characteristics of glaucoma patients would have been helpful. Whether patients showed MRI abnormalities such as white matter hyperdensities as often seen in glaucoma would also be relevant. Multiple thresholds were set by the investigators and so it is not clear whether they were masked to glaucoma and control information during voxelbased morphometry analysis.
The anterior and posterior parts of the visual cortex were studied, however, the methods used to delineate these volumes of interest were not based on specific referenced human brain maps or functional MRI of the studied groups. The grey matter density within each voxel in the x, y and z coordinates within a structure was compared between control and glaucoma groups. The reason for lack of correction for multiple t-testing is not provided.
The authors point out several inherent limitations of vortex-based morphometry in their study, including inter-subject spatial normalization of different subjects with gyral variants, and potential sources of error and bias that can be introduced at the different stages of vortex-based morphometry study.1 In addition, some of the limitations specific to the subjects such as younger age of the controls compared to the glaucoma group are also discussed. In spite of these limitations, the study contributes to the body of knowledge on degeneration in the visual cortex in glaucoma, and supports previous functional MRI studies of the cortex in glaucoma.2 Comparison of vortex-based morphometry to manual and visual measurements3 of visual cortex in MRI neuroimaging, and neuropathological specimens can provide additional confidence in the biological validity of this type of vortex-based morphometry.
References
- Ridgway GR, Henley, SMD, Rohrer JD, Scahill RI, Warren JD, and Fox NC. Ten simple rules for reporting voxel-based morphometry studies. Neuroimage 2008; 40: 1429-1435.
- Duncan RO, Sample PA, Weinreb RN, Bowd C, Zangwill LM. Retinotopic organization of primary visual cortex in glaucoma: Comparing fMRI measurements of cortical function with visual field loss. Prog Retin Eye Res 2007; 26: 38-56.
- Whitwell J.L. Voxel-based morphometry: An automated technique for assessing structural changes in the brain. Journal of Neuroscience 2009; 29: 9661-9664.
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