ANIMALS - Neuroscientists show that monkeys can decide to call out or keep silent

"Should I say something or not?" Human beings are not alone in pondering this dilemma -- animals also face decisions when they communicate by voice. Neurobiologists have now demonstrated that nerve cells in the brain signal the targeted initiation of calls -- forming the basis of voluntary vocal expression ...

http://www.sciencedaily.com/releases/2013/09/130906102147.ht