Neuroscientists Reveal Monkeys Can Choose to Speak or Keep Silent

Whether or not you say something may seem like an inherently human trait, yet animals also face this dilemma. It turns out that monkeys also can make the choice when it comes to whether or not to keep silent.

When we speak, we intentionally say what we think or, sometimes, consciously withhold information. Animals, in contrast, usually make sounds according to how they feel at the moment. In fact, previous research seemed to indicate that even primates made sounds as a reflex based on their mood rather than on any sort of conscious decision. In order to learn a little bit more about this process of "speaking" among animals, the researchers turned to rhesus monkeys.

In this experiment, the researchers taught rhesus monkeys to call out quickly when a spot appeared on a computer screen. While the monkeys solved these puzzles, the researchers took measurements of their prefrontal cortex. This allowed the scientists to see the interactions taking place there during the course of the study.

When the monkeys saw the spot of light on the screen, the researchers saw the nerve cells in their brains become active. But if the monkeys simply called out spontaneously, these nerve cells were not activated. Therefore, the cells did not signal for just any vocalization--only calls that the monkeys actively decided to make.

"We want to understand the physiological mechanisms in the brain which lead to the voluntary production of calls because it played a key role in the evolution of human ability to use speech." said Steffen Hage, one of the researchers, in a news release.

The new research reveals a little bit more about the neurobiological foundations of vocalization. In fact, it reveals how neural cells in the brain catalyze the production of controlled vocal noises. The findings could also help researchers better understand disorders that occur within this part of the human brain and which can lead to severe speech disorders or even complete loss of speech in a patient.

The findings are published in the journal Nature Communications.