New brain circuit discovery could explain how we detect faces

Gongchen Yu, Ph.D., Leor Katz, Ph.D., and Richard Krauzlis, Ph.D. Credit: Dustin Hays, National Eye Institute.

Scientists at the National Institutes of Health (NIH) have discovered a brain circuit in primates that rapidly detects faces.

This finding not only helps explain how primates, including humans, sense and recognize faces, but it could also shed light on conditions like autism, where face detection and recognition are often impaired from early childhood.

The newly found circuit starts with an ancient part of the brain called the superior colliculus. This part of the brain can trigger the eyes and head to turn for a better view of a face.

Once we get a clearer look, other brain areas in the temporal cortex can engage in more complex facial recognition. The study was published in the journal Neuron.

“Quick recognition of faces is a key skill in humans and other primates,” said Richard Krauzlis, Ph.D., of NIH’s National Eye Institute (NEI) and senior author of the study.

“This newly discovered circuit explains how we’re able to quickly detect and look at faces, even if they first show up in the peripheral visual field where visual acuity is poor.

This circuit could be what spotlights faces to help the brain learn to recognize individuals and understand complex facial expressions, helping us acquire important social interaction skills.”

In adult primates, the brain has specialized regions in the temporal cortex called “face patches” that help recognize and distinguish individuals by their facial features.

However, facial recognition depends on fine details provided by the eye’s central vision. To recognize a face, we first need to look directly at it.

When babies are born, they lack the high acuity vision needed to see fine details of faces, and the face-specific areas of the cortex don’t develop until later. Despite this, babies often look at faces very early in life, suggesting another process is at play.

These observations led scientists to question how the brain shifts the eyes towards a face to see fine details, what provides this face preference before the brain’s “face patches” develop, and how these “face patches” learn to understand faces.

Krauzlis and his team hypothesized that the superior colliculus—known to detect objects—might be the missing link. This part of the midbrain tells the rest of the brain if something is present somewhere.

It functions extremely quickly and connects directly to the motor parts of the brain, directing eye movements towards objects of interest.

To test this, researchers showed images of faces, non-face biological objects (like hands), and other items to adult monkeys and recorded the responses in the superior colliculus.

They found that within 40 milliseconds, more than half the neurons they measured responded more strongly to images of faces compared to other types of objects.

This face-specific detection was much faster than the detection of other objects, which took about 100 milliseconds.

The researchers also discovered that while the superior colliculus can receive visual information directly from the eye, this face-detection process requires input from the early part of the visual cortex.

Since the superior colliculus also reconnects back to the visual cortex later in the processing pathway, this circuit likely helps highlight important objects, like faces.

“We believe this face-preference circuit may actually drive the development of the brain’s more advanced facial recognition processes,” said Krauzlis. “If so, deficits in this face preference in the superior colliculus might play a role in autism.”

This discovery provides a deeper understanding of how we detect and recognize faces. It could lead to better understanding and treatment of conditions like autism, where face recognition is often challenging.

By studying this brain circuit, scientists hope to uncover new ways to support individuals with face recognition difficulties, improving their social interactions and overall quality of life.