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Poster A49, Tuesday, August 20, 2019, 10:15 am – 12:00 pm, Restaurant Hall

Revisiting the connectional neuroanatomy of pars opercularis and the ventral precentral fiber intersection area using data from the Human Connectome Project

Baboyan Vatche1, Gregory Hickok1;1University of California, Irvine

Evidence from diffusion imaging, postmortem dissection, and direct electrical subcortical stimulation studies indicate that a variety of association fibers within the language network converge near the ventrolateral prefrontal cortex. More recently, these studies suggest that the fiber organization of the ventral precentral cortex (vPMC) is different from classical descriptions, and is a critical projection site for not only pyramidal pathways, but also for motor and auditory association fibers involved in speech function. Despite this fact, this densely connected area - recently referred to as the ventral precentral fiber intersection area - remains poorly understood due to it's complex organization. Using data from 100 subjects from the Human Connectome Project, we sought to revisit the connectional neuroanatomy of two central hubs within the language network: vPMC and Brodmann Area 44. Probabilistic fiber tractography was performed on the multi-shell dMRI data for both BA 44 and vPMC, bilaterally. To restrict analysis to dorsal speech production fibers, the tracking algorithm discarded any streamlines passing through the temporal stem region, thereby removing ventral stream pathways involved in the widely distributed semantic network. Results were then projected onto standardized surfaces to characterize and compare the connectivity of vPMC and BA 44. First, we performed a Principal Components Analysis (PCA) along the 2D surface mesh, which for each subregion, revealed a single component accounting for 70% of the total variance in connectivity across each group while no other component accounted for more than 2% of total variance. The principal component for vPMC was comprised of weights attributed to nodes within the ventral precentral sulcus, the supplementary motor area (SMA), the posterior insular cortex, the supramarginal gyrus, and the planum temporale. Conversely, BA 44 was comprised of weights attributed to nodes in the inferior frontal sulcus (i.e., dorsal BA 44), the pre-SMA, middle insular cortex, and a stronger contribution to the pSTS than what was seen with vPMC. This finding suggests that BA 44 is the primary projection site for the arcuate fasciculus and not the vPMC; contrary to previous reports. Second, we directly compared the differences in multivariate connectivity patterns between each subregion, by computing the average connectivity within each of the 180 brain areas comprising the HCP Multimodal Parcellation atlas. The multivariate matrix for each subregion was then fed into a Linear Discriminant Analysis (LDA) classification algorithm to establish the linear combinations of brain areas producing the best separation between the two subregions. The LDA algorithm, by assigning negative weights to areas mapping onto BA 44 and positive weights mapping onto the vPMC, revealed sets of regions comprising parallel dorsal streams; with vPMC being associated with the somatosensory cortex, SMA, and the planum temporale while BA 44 showed associations with distributed areas along the superior temporal sulcus, preSMA, and area 55b. This finding was then corroborated by a third analysis, where a univariate GLM comparing differences in connectivity at each node of the surface revealed to distinct clusters, with vPMC showing a Fronto-Parietal-SMA preference and BA 44 showing a Fronto-Temporal-preSMA preference in connectivity.

Themes: Methods, Language Production
Method: White Matter Imaging (dMRI, DSI, DKI)

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