in the early cro magnun period..humanoid skulls had hinges on them..frequently when running from a mammoth, these hinges would let loose and the top of the skull would flap a bit and the dust from the chase would get in there...so...these early humans would take out each other's brains and wash them in a combination of mammoth blood and saber tooth tiger saliva...

Brainwashing (also known as thought reform or re-education) consists of any effort aimed at instilling certain attitudes and beliefs in a person — beliefs sometimes unwelcome or in conflict with the person's prior beliefs and knowledge. Motives for brainwashing may include the aim of affecting that individual's value system and subsequent thought-patterns and behaviors. The English words "re-educate" and "re-education", which the Oxford English Dictionary attests in general senses from 1808, began in the 1940s to express specifically political connotations. George Orwell mentioned in Animal Farm (1945) "the Wild Comrades' Re-education Committee (the object of this was to tame the rats and rabbits)"; and Arthur Koestler in The Age of Longing (1951) wrote of "revolutionary vigilance,.. and discipline, and re-education camps". The term "brainwashing" first came into use in the English language in the 1950s. The OED records its earliest known English-language usage of "brain-washing" by E. Hunter in New Leader on 7 October 1950. John D. Marks claimed that Edward Hunter was "later revealed" to have worked undercover for the Central Intelligence Agency (CIA) Source: http://en.wikipedia.org/wiki/Brainwashing

sounds like a surgical procedure of some sort.