Milgram claimed obedience transitions rest on neural shifts unobservable at the chemical level.

Evidence

Where in a human being shall we find the switch that controls the transition from an autonomous to a systemic mode? No less than in the case of automata, there is certainly an alteration in the internal operations of the person, and these, no doubt, reduce to shifts in patterns of neural functioning. Chemical inhibitors and disinhibitors alter the probability of certain neural pathways and sequences being used. But it is totally beyond our technical skill to specify this event at the chemoneurological level. (p. 133) Milgram also made clear how seriously he takes his concept. — John T. Jost and Jim Sidanius, Political Psychology, 3931