Christians converting to Islam or any other religion or vice versamay have been brainwashed.
"Brainwashing is not just an issue of political prisoners, but also a problem for all human beings who decide to radically change their lives. Before brainwashing, a person has a set of beliefs, but afterwards they believe something radically different. These new beliefs are adopted in a very short amount of time, rather than built up over a lifetime.
Famed physiologist Ivan Pavlov (1849-1936), studied the nervous system of animals. Pavlov carried out an experiment where he put some dogs under extreme stress until they crumbled and their mind literally shut off. Pavlov found that the behavior of the dogs drastically changed. Firstly, they forgot most previous teachings, and secondly, if he taught them a new behavior shortly after the breakdown, it became deeply embedded.
The same logic applied to humans. In his book ‘Battle for the Mind’ (1957), he wrote that men can be brainwashed “not by persuasive indoctrination alone, but also by imposing intolerable strains on a normally functioning brain. Humans have to go under intense emotional stress in order to obliterate their previous beliefs and take on new ones.
Philosopher William James pointed out that emotional stress can include intense experiences such as grief and heartbreak. For example, abusive relationships, extreme happiness, and extreme insecurity can all pass for intense emotional experiences that can cause drastic mental change.
