Synapse is former S.H.I.E.L.D agent Max Mullins who is in the employ of the Kingpin in Paris.
Synapse has the ability to disrupt a persons brain and “rewire” it to his liking. This does not, however, appear to work on the strong willed or on a person who’s mind has already been altered.  When he tried to rewire DD’s mind in the “Flying Blind” arc occurring thru issues #376-379,”Laurent Levasseur, agent of S.H.E.I.L.D.” smiled and thanked him.Â