This page maybe useful Its about what happens to your brain when you're drunk

Because you use primitive parts of your brain when you are drunk and the parts that influence cognitive decision making are inhibited; you are more likely to act in a more primal animalistic way. People forget that humans are merely domesticed apes and just like dogs; which are domestic wolves; they still have that primordial switch that results them in doing what is classified as obscene thoughts, actions or behaviours. This pretty much explains why a person is more likely to commit a rape when drunk or a physical assault or say something "without thinking".

Everyone has a primal instinct within, but as intelligent creatures; most adults have the ability to CHOSE which part of the brain they will use (hence why people can contain emotion). This ability is generaly lost when under the influence of alcohol and other potent substances.