graph theory, part deux

At risk of turning this blog into “the fMRI graph theory analysis papers” (which would probably attract more readers) here are a couple of better renderings and/or conceptions of the default-mode and task-positive networks. I’ve included only edges that represent significant correlations across subjects — the first as quantified by t-test on Fisher-transformed correlations, the second as quantified by Wilcoxon rank-sum test on raw correlations. I’ve also used a layout scheme that tries to capture the proximity between nodes.



The parametric and nonparametric edge definitions yield pretty much exactly the same organization, with DMN and task-positive networks highly intraconnected (is that a word?) but sparsely interconnected. Both approaches also capture an isolated subnetwork in bilateral parahippocampal cortex and accurately ostracize the cerebellar ROI, which isn’t actually part of the DMN or task-positive networks — it was supposed to be posterior cingulate,but I messed it up.

Another slightly subtler feature captured by both approaches is the particular inter-network edges, with positive connectivity between the DMN superior frontal ROIs (R/LSF) and task-positive dorsolateral PFC (R/LDLP) on the same side, and between the DMN “parietal” ROIs and task-positive ipsilateral loci in the intraparietal sulcus. Edited after I realized I posted the same image twice: The parietal connectivity is consistent across correlation metrics but the prefrontal connectivity isn’t. It looks like there’s some symmetry in the medial prefrontal and inferotemporal connectivity within the DMN as well; the medial prefrontal connectivity is also symmetric in the parametric graph but not so much in the nonparametric graph.

Still need to work on rendering edge weights. But these graphs are much nicer.


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