The act of altering a person's existing thoughts and beliefs through violence, drugs, and psychological pressure. This may involve changes in the person's values, memories, or even personality.

Not all of the next-generation Genome Soldiers willingly joined in FOXHOUND's insurrection. Many were brainwashed through Psycho Mantis's psycho-dives into their minds. After Solid Snake defeated Psycho Mantis, the brainwashing gradually wore off.