Create a new graph after merging multiple vertices based on brain lobe and hemisphere membership.
contract_brainGraph(g)An igraph graph object
A new igraph graph object
The vertex size of the resultant graph is equal to the number of vertices in each lobe (in the input graph). The x- and y- coordinates of the new vertices are equal to the mean coordinates of the lobe vertices of the original graph. The new edge weight is equal to the number of inter-lobular connections of the original graph.