  We study the transition in the functional networks that characterize the
human brains' conscious-state to an unconscious subliminal state of perception
by using k-core percolation. We find that the most inner core (i.e., the most
connected kernel) of the conscious-state functional network corresponds to
areas which remain functionally active when the brain transitions from the
conscious-state to the subliminal-state. That is, the inner core of the
conscious network coincides with the subliminal-state. Mathematical modeling
allows to interpret the conscious to subliminal transition as driven by k-core
percolation, through which the conscious state is lost by the inactivation of
the peripheral k-shells of the conscious functional network. Thus, the inner
core and most robust component of the conscious brain corresponds to the
unconscious subliminal state. This finding imposes constraints to theoretical
models of consciousness, in that the location of the core of the functional
brain network is in the unconscious part of the brain rather than in the
conscious state as previously thought.
