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

Researchers at the National Institutes of Health (NIH) have identified a brain circuit in primates that quickly detects faces. The discovery not only helps to explain how primates perceive and recognize faces, but also has potential implications for understanding conditions such as autism, where face detection and recognition are often affected from an early age. The newly identified circuit first activates an ancient part of the brain known as the superior colliculus, which then prompts the eyes and head to turn for a better view. This improved perspective allows different areas of the brain in the temporal cortex to participate in more intricate 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 the senior author of the study. “This newly discovered circuit explains how we can 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 develops specialized regions of the temporal cortex called “face patches” that enable the recognition and differentiation of individuals based on their facial features. However, facial recognition relies on the precise details captured by the eye’s high acuity central vision. In order to recognize a face, we must first look directly at it.

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

Krauzlis and his colleagues suggested that the superior colliculus, which is responsible for detecting objects, could be the missing link. Located in the midbrain, it informs the rest of the brain about the presence of something, without identifying what the object is. This process occurs very quickly and directly influences the motor functions of the brain, guiding eye movements towards objects of interest and triggering reflexive reactions such as flinching when an object is seen in the peripheral vision.

Gongchen Yu, Ph.D., and Leor Katz, Ph.D., co-first authors of a study, investigated whether the superior colliculus contributes to face detection. They presented a variety of images, such as faces, body parts, fruit, and man-made objects, to adult monkeys in their peripheral vision. Then, they monitored the neuronal responses in the monkeys’ superior colliculus.

Previous studies suggested that the superior colliculus detected objects without distinguishing what the object was. However, a new study by Krauzlis and colleagues 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. Some additional neurons eventually displayed preferences for other types of objects, but not until 100 milliseconds. In other words, the detection of faces was much faster and preferred by a large proportion of the measured neurons compared to other objects.

The researchers determined that the superior colliculus requires input from the early part of the visual cortex for object detection, instead of receiving visual information directly from the eye.

Since the superior colliculus also reconnects with the visual cortex later in the visual processing pathway, scientists suspect that this circuit provides a mechanism to emphasize the importance of certain objects.

“We believe that this circuit for preferring faces may actually drive the development of the brain’s more advanced processes for recognizing faces,” said Krauzlis. “If so, deficiencies in this preference for faces in the superior colliculus might play a role in autism.”