  Directed graphs are widely used in modelling of nonsymmetric relations in
various sciences and engineering disciplines. We discuss invariants of strongly
connected directed graphs - minimal number of vertices or edges necessary to
remove to make remaining graphs not strongly connected. By analogy with
undirected graphs these invariants are called strong vertex/edge
connectivities. We review some properties of these invariants. Computational
results for some publicly available connectome graphs used in neuroscience are
described.
