Researchers probing the brains of monkeys may have found a new clue that could help them better understand where human speech comes from.
They discovered neural networks in the brains of monkeys that could very well be the evolutionary source of social communication, including something as sophisticated as human speech.
Neural Circuits In Monkey Brain Offer A Clue
In a new paper published in the journal Neuron, a team of researchers at the Rockefeller University argue that certain neural circuits could have given rise to man's capacity for speech.
These circuits include areas in the brain associated with recognizing faces, generating facial expressions, and processing emotions.
Lead author Winrich Freiwald, professor at Rockefeller's Laboratory of Neural Systems, has previously pinpointed regions in the brains of monkeys responsible for recognizing faces. These neural circuits are very similar to those in the human brain.
However, no studies investigating how these circuits light up during social communication have been done before.
MRI Scans Of Monkey Brains
In a first-of-its-kind study, Freiwald and his team set out to take MRI scans of the brains of rhesus macaque monkeys while making facial expressions during active social communication.
The subject monkeys were shown video clips of other monkeys. In some of the clips, the monkeys were looking away, simulating situations where the subject monkeys were simply observing social communication but not participating in it.
In other clips, the monkeys looked like they were looking directly at the subject monkeys, similar to situations of active face-to-face communication.
The researchers found that when the monkeys in the videos made lip-smacking gestures, the subject monkeys did the same as well. However, the subject monkeys only did so when the monkeys in the video mimicked eye-to-eye contact with them.
Results Of Brain Scans
The brain scans showed that active social communication lit up a region in the monkey's brains associated with recognizing faces, something that Freiwald and his team have already expected based on previous studies.
This stimulates brain regions involved with creating facial expressions as the subject monkeys responded to the lip-smacking gesture.
However, the researchers found that activation did not happen in a straightforward, linear manner.
They also learned that eye-to-eye social communications lit up a third neural circuit involved with emotion, suggesting that specific areas in the brain perform functions related to social communication.
Lip-Smacking Gestures As Precursor To Speech
On the other hand, creating facial expressions to respond to the monkeys in the video generated a different brain activation pattern.
When the subject monkeys made lip-smacking gestures, the Broca's area in the frontal lobe lit up. This is the same part of the human brain associated with speech.
Based on the findings, the researchers believe that facial expressions could be the precursor to human speech.
"Understanding this in monkeys will help us understand communication in humans, where things are so much more complicated," Freiwald says.
Photo: Sammy (Ka Chi) Sam | Flickr