The different EM field theories disagree as to the role of the proposed conscious EM field on brain function. In McFadden's cemi field theory, as well as in Drs Fingelkurts' Brain-Mind Operational Architectonics theory, the brain's global EM field modifies the electric charges across neural membranes, and thereby influences the probability that particular neurons will fire, providing a feed-back loop that drives free will. However, in the theories of Susan Pockett and E. Roy John, there is no necessary causal link between the conscious EM field and our consciously willed actions.