Title: The Frequent Network Neighborhood Mapping of the Human Hippocampus Shows Much More Frequent Neighbor Sets in Males Than in Females,
Abstract: In the study of the human connectome, the vertices and the edges of the
network of the human brain are analyzed: the vertices of the graphs are the
anatomically identified gray matter areas of the subjects; this set is exactly
the same for all the subjects. The edges of the graphs correspond to the axonal
fibers, connecting these areas. In the biological applications of graph theory,
it happens very rarely that scientists examine numerous large graphs on the
very same, labeled vertex set. Exactly this is the case in the study of the
connectomes. Because of the particularity of these sets of graphs, novel,
robust methods need to be developed for their analysis. Here we introduce the
new method of the Frequent Network Neighborhood Mapping for the connectome,
which serves as a robust identification of the neighborhoods of given vertices
of special interest in the graph. We apply the novel method for mapping the
neighborhoods of the human hippocampus and discover strong statistical
asymmetries between the connectomes of the sexes, computed from the Human
Connectome Project. We analyze 413 braingraphs, each with 463 nodes. We show
that the hippocampi of men have much more significantly frequent neighbor sets
than women; therefore, in a sense, the connections of the hippocampi are more
regularly distributed in men and more varied in women. Our results are in
contrast to the volumetric studies of the human hippocampus, where it was shown
that the relative volume of the hippocampus is the same in men and women.