Functional connectivity for somatosensory and motor cortex in spastic diplegia

Abstract

Functional connectivity (fcMRI) was analyzed in individuals with spastic diplegia and age-matched controls. Pearson correlations (r-values) were computed between resting state spontaneous activity in selected seed regions (sROI) and each voxel throughout the brain. Seed ROI were centered on foci activated by tactile stimulation of the second fingertip in somatosensory and parietal dorsal attention regions. The group with diplegia showed significantly expanded networks for the somatomotor but not dorsal attention areas. These expanded networks overran nearly all topological representations in somatosensory and motor areas despite a sROI in a fingertip focus. A possible underlying cause for altered fcMRI in the group with dipegia, and generally sensorimotor deficits in spastic diplegia, is that prenatal third trimester white-matter injury leads to localized damage to subplate neurons. We hypothesize that intracortical connections become dominant in spastic diplegia through successful competition with diminished or absent thalamocortical inputs. Similar to the effects of subplate ablations on ocular dominance columns (Kanold and Shatz, Neuron 2006;51:627-638), a spike timing-dependent plasticity model is proposed to explain a shift towards intracortical inputs.

Figure 1

Functional connectivity maps for left hemisphere somatosensory seed regions (L BA1 and L OP 1). Random effect t-maps of r- to Z-transformed averages per group. Seed locations are marked with green spheres.

Figure 2

Average resting state MR signal timecourse from seed regions L BA1 and L OP 1 in diplegia and control groups.

Figure 3

Group contrasts (t-test maps) of functional connectivity results for different seed regions (L BA1, L OP 1, and L BA7A). Black borders surround regions where permutation analyses (Nordahl et al. 2007) indicated significant group differences in functional connectivity maps (see Methods).

Figure 4

Average area-proportion indices per group. (A) Selected cortical areas used for area extent analyses. Top two rows show average inflated cortical surface and bottom row shows flattened surface from PALS-B12 atlas (Van Essen 2005; Van Essen and Dierker 2007). Boundary of postcentral gyrus (PCG) based on conjunction of Brodmann areas 3, 1, and 2. These and other BA borders were based on maps from the PALS-B12 atlas. Boundary of parietal operculum (PO) based on conjunction of OP subdivisions 1, 3, and 4 (Burton et al. 2008b). (B) Area proportions for seed regions in left primary and secondary somatosensory cortex, L BA1 and L OP 1, respectively. p-Values of group contrast t-test results are noted above graphs. All group contrast t-test results were significant. Error bars are SEMs. Abbreviations: BA4, Brodmann area 4; BA6, Brodmann area 6; BA24, Brodmann area 24; BA42, Brodmann area 42 (primary auditory); PCG, postcentral gyrus; PO, parietal operculum; FCCP, diplegia; FCN, controls.