The brain interprets what we see in our environment even the expressions of other people. Researchers have revealed what part of the brain is responsible for recognizing people's facial expression.

The researchers from Ohio State University (OSU) showed that posterior superior temporal sulcus or pSTS, which is located at right side of the brain behind the ear, is the one responsible for facial expression recognition.

With the use of fMRI or functional magnetic resonance imaging, the researchers saw an increased blood flow on the brain's pSTS when the subjects looked at the facial expressions shown to them.

The study also discovered that the nerve pattern in pSTS recognizes the movement of facial muscles. For example, it recognizes the pattern of furrowed brows and the upturn of the lips when smiling.

"That suggests that our brains decode facial expressions by adding up sets of key muscle movements in the face of the person we are looking at," said cognitive scientist and professor Aleix Martinez of electrical and computer engineering at OSU.

Martinez's team placed 10 participants under fMRI machine wherein they were showed 1,000 facial expressions that corresponded to seven emotional categories, namely disgusted, happily disgusted, fearfully disgusted, happily surprised, fearfully surprised, angrily surprised and sadly fearful.

Even though the categories shown were a mix of negative and positive expressions, there is a similarity among them. For example, though they differ in other facial movements, happily, fearfully and angrily surprised all showed raised eyebrows.

The researchers also invented a machine learning algorithm that identifies the facial expression of a person with the use of the fMRI data.

According to Martinez humans make use of a very large number of facial expressions to show an emotion aside from non-verbal communication and language.

"This work could have a variety of applications, helping us not only understand how the brain processes facial expressions, but ultimately how this process may differ in people with autism, for example," said Director Julie Golomb, Vision and Cognitive Neuroscience Lab, OSU and one of the authors of the research.

The study was funded by National Institutes of Health and Alfred P. Sloan Foundation.