Ultra-high field parallel imaging of the superior parietal lobule during mental maze solving

Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota Medical School, Minneapolis, MN 55455, USA.
Experimental Brain Research (Impact Factor: 2.04). 07/2008; 187(4):551-61. DOI: 10.1007/s00221-008-1318-8
Source: PubMed


We used ultra-high field (7 T) fMRI and parallel imaging to scan the superior parietal lobule (SPL) of human subjects as they mentally traversed a maze path in one of four directions (up, down, left, right). A counterbalanced design for maze presentation and a quasi-isotropic voxel (1.46 x 1.46 x 2 mm thick) collection were implemented. Fifty-one percent of single voxels in the SPL were tuned to the direction of the maze path. Tuned voxels were distributed throughout the SPL, bilaterally. A nearest neighbor analysis revealed a "honeycomb" arrangement such that voxels tuned to a particular direction tended to occur in clusters. Three-dimensional (3D) directional clusters were identified in SPL as oriented centroids traversing the cortical depth. There were 13 same-direction clusters per hemisphere containing 22 voxels per cluster, on the average; the mean nearest-neighbor, same-direction intercluster distance was 9.4 mm. These results provide a much finer detail of the directional tuning in SPL, as compared to those obtained previously at 4 T (Gourtzelidis et al. Exp Brain Res 165:273-282, 2005). The more accurate estimates of quantitative clustering parameters in 3D brain space in this study were made possible by the higher signal-to-noise and contrast-to-noise ratios afforded by the higher magnetic field of 7 T as well as the quasi-isotropic design of voxel data collection.

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    • "Given the involvement of the PPC in the control of attention , one might expect to observe a set size effect in this region because the demand on visual attention presumably increases with set size. For example, it is reasonable to think that the number and direction ( Jerde et al., 2008; Gourtzelidis et al., 2005) of covert shifts of attention would increase with the number of potential targets, and loaddependent increases have been observed in PPC for attention and working memory (Mayer et al., 2007). However, we did not find a set size effect in PPC. "
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