FV 2 Reduced spatial variability in cortical working memory networks after macro-anatomical alignment – Converging evidence from multiple fMRI studies

Publication date: October 2017
Source:Clinical Neurophysiology, Volume 128, Issue 10
Author(s): R. Bittner, A. Seitz, P. Hahn, E. Raspor, C. Novak, D. Linden, R. Goebel, A. Reif
IntroductionReducing the spatial variability in group analyses is an important issue in functional neuroimaging studies. Commonly volume-based whole-brain alignment procedures are used to provide a common analysis space and to align brains across subjects. Inter-individual differences in the cortical folding pattern are an important source of spatial variability. However, volume based alignment methods do not take this factor into account. By contrast, surface based alignment procedures have been shown to significantly improve macro-anatomical alignment and increase the overlap of functional activation. However, this has primarily been demonstrated for sensory and motor paradigms, but not for higher cognitive functions such as working memory. However, working memory is particularly relevant for investigating the neurophysiological and genetic mechanisms of neuropsychiatric disorders such as schizophrenia.MethodsWe applied the same high-resolution, multiscale curvature driven cortex based alignment procedure to three separate fMRI data sets using Brain Voyager QX 2.8. Anatomical scans were segmented along the white–gray matter boundary. Cortical hemispheres were reconstructed and morphed into spherical representations. Each cortical folding pattern was aligned to a dynamically updated group average through iterative morphing following a coarse-to-fine matching strategy. In a spatial working memory study with 32 healthy participants (study 1), we studied the impact of this macroanatomical alignment procedure on spatial variability of functional activation in the working memory network. In a separate spatial working memory imaging genetics study with 112 healthy participants (study 2), we examined a panel of SNPs previously reported in imaging genetics studies, and investigated whether macroanatomical alignment increased the likelihood of detecting effects of these SNPs on activation of the cortical working memory network. In a study of visual working memory dysfunction in schizophrenia with 17 patients with schizophrenia and 17 matched controls (study 3), we investigated, whether macroanatomical alignment differentially affects patients with schizophrenia, which are characterized by increased interindividual cortical anatomical variability.ResultsIn study 1 we observed a reduction of spatial variability of functional activation by roughly 30% in key frontal and parietal areas of the working memory network and a small but robust increase in activation strength after macroanatomical alignment. In study 2 we observed, that macroanatomical alignment increased the likelihood to detect significant effects of individual SNPs on working memory related brain activation. In study 3 spatial variability of functional activation decreased in both groups, but this effect was more pronounced in patients.ConclusionsCortex based alignment substantially reduces the spatial variability of functional activation during working memory. This also improves the effect sizes of imaging genetics studies. Furthermore, our method appears to correct the increased interindividual cortical anatomical variability found in schizophrenia to a considerable degree, addressing an important confound in neuroimaging studies of this disorder. We conclude that the benefits of cortex based alignment warrant its more frequent use in fMRI studies of higher cognitive processes in healthy and patient populations.



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