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. 2005 Aug 23;102(34):12212-7.
doi: 10.1073/pnas.0407259102. Epub 2005 Aug 15.

Choice reaction time performance correlates with diffusion anisotropy in white matter pathways supporting visuospatial attention

David S Tuch  1 , David H Salat, Jonathan J Wisco, Alexandra K Zaleta, Nathanael D Hevelone, H Diana Rosas
Affiliations

Choice reaction time performance correlates with diffusion anisotropy in white matter pathways supporting visuospatial attention

David S Tuch et al. Proc Natl Acad Sci U S A. .

Abstract

Humans exhibit significant interindividual variability in behavioral reaction time (RT) performance yet the underlying neural mechanisms for this variability remain largely unknown. It has been proposed that interindividual variability in RT performance may be due to differences in white matter (WM) physiological properties, although such a relationship has never been demonstrated in cortical projection or association pathways in healthy young adults. Using diffusion tensor MRI (DTI), we sought to test whether diffusion tensor fractional anisotropy (FA), a measure of the orientational coherence of water self-diffusion, is regionally correlated with RT on a visual self-paced choice RT (CRT) task. CRT was found to be significantly correlated with FA in projection and association pathways supporting visuospatial attention including the right optic radiation, right posterior thalamus, and right medial precuneus WM. Significant correlations were also observed in left superior temporal sulcus WM and the left parietal operculum. The lateralization of the CRT-FA correlation to right visual and parietal WM pathways is consistent with the specialization of right visual and parietal cortices for visuospatial attention. The localization of the CRT-FA correlations to predominantly visual and parietal WM pathways, but not to motor pathways or the corpus callosum indicates that individual differences in visual CRT performance are associated with variations in the WM underlying the visuospatial attention network as opposed to pathways supporting motor movement or interhemispheric transmission.

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Figures

Fig. 1.
Fig. 1.
Behavioral RTs on the CRT task (n = 12). The left column gives the participants' RT for native performance (block 1) and the right column gives the ΔRT for within-session improvement (block 1 minus block 6).
Fig. 2.
Fig. 2.
CRT performance is correlated with FA in the right optic radiation but not the left optic radiation. The plots show the native CRT and the ROI FA measurements (±SEM) from the right and left optic radiation. CRT and FA are significantly correlated in the right optic radiation (rs = 0.83, P = 1.7 × 10-3) but not the left optic radiation (rs = 0.31, P = not significant) (Table 2). The solid line indicates the linear fit, and the dashed line indicates the 85% confidence interval for the fit.
Fig. 3.
Fig. 3.
Individuals with fast CRT have low FA in the right optic radiation. MNI-normalized FA maps for the representative participant (A) and the group average FA map (B) are shown. The yellow box indicates a region of interest (ROI) at the junction between the right optic radiation and the posterior forceps of the corpus callosum. (C) FA maps from each of the 12 participants taken from the ROI. Each participant's CRT for block 1 is shown at the bottom right corner of that participant's map. The ROIs are ordered from left to right and top to bottom in order of increasing RT. Note the increase in FA in the optic radiation with increasing CRT. The images are displayed in radiological convention so that the left direction on the page corresponds to the right direction on the anatomy and vice versa. The radiological display convention is used throughout.
Fig. 4.
Fig. 4.
CRT and FA are correlated in the right visual pathway. The Spearman correlation coefficient (rs) between CRT and FA is displayed as a colored map overlaid on the MNI individual T1 template. The small frames show six axial slices through the optic radiation. The superior-inferior level of the axial slices is indicated by the yellow lines in the sagittal images at top right and by the MNI Z-coordinate at the bottom right of each frame. The sagittal images at top right are the MNI individual T1 template (Left) and the group average FA map (Right). The correlation map shows the trajectory of the right visual pathway from lateral geniculate nucleus (LGN) through Meyer's loop (ML) to the optic radiation (OR), terminating at the junction between the optic radiation and the posterior forceps of the corpus callosum (OR-PF). Multiple comparisons-corrected significance levels of P < 0.05 and P < 0.10 are achieved by critical correlation values of |rs| > 0.867 and |rs| > 0.839, respectively.
Fig. 5.
Fig. 5.
Within-session improvement in CRT is correlated with FA in the posterior thalamus. (A) The Spearman correlation coefficient map for ΔCRT-FA is shown superimposed on the MNI individual T1 template (Upper and Lower Left), and on a coronal view of the group average FA map (Lower Right). The color scale for the correlation coefficient map is the same as described in Fig. 4. The correlation localizes to left and right posterior thalamus. (B) Diffusion tensor map of the left thalamus from the representative participant. The group ΔCRT-FA correlation coefficient map is shown superimposed as a red-yellow color scale image on a diffusion tensor cuboid map. The color scale for the correlation map is the same as described in Fig. 4. The region of significant correlation (indicated by the asterisk) localizes to the border between the pulvinar nucleus (red, medial-lateral) and the lateral geniculate nucleus (blue-red, posterior-medial to inferior-lateral). The cuboidal glyphs depict the 3D diffusion tensor at each voxel location. The axes of each cuboid are oriented and scaled according to the local diffusion tensor eigensystem. An additional scaling factor of sqrt(FA) is also applied. The cuboids are colored according the orientation of the principal eigenvector with red indicating medial-lateral, green anterior-posterior, and blue superior-inferior (59). The directional color scheme is also indicated by the red-green-blue crossbars in the upper right corner. LGN, lateral geniculate nucleus; MD, mediodorsal nucleus; ML, Meyer's loop; PLIC, posterior limb of the internal capsule; Pulv, pulvinar nucleus; VPL, ventral posterior lateral nucleus (60). Note that the slice is shown at an oblique angle.
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