Press release
Tuesday July 2, 2024
The results obtained in non-human primates could shed light on how our brains develop their facial recognition abilities.
Scientists at the National Institutes of Health (NIH) have discovered a brain circuit in primates that rapidly detects faces. The findings not only help explain how primates perceive and recognize faces, but could also have implications for understanding conditions such as autism, where face detection and recognition are often impaired from early childhood. The newly discovered circuit first activates an ancient part of the brain called the superior colliculus, which can then trigger the eye and head to rotate to see better. This improved vision allows different brain areas in the temporal cortex to engage in more complex face recognition. The study was published in the journal Neuron.
“Rapid face recognition is a critical skill in humans and other primates,” said Richard Krauzlis, Ph.D., of the NIH’s National Eye Institute (NEI) and lead author of the study. “This newly discovered circuit explains how we are able to quickly detect and look at faces, even when they first appear in the peripheral visual field where visual acuity is low. This circuit may be the one that highlights 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 spots” that allow individuals to be recognized and distinguished by their facial features. However, facial recognition depends on the fine details provided by the eye’s highly acute central vision; to recognize a face, one must first look at it directly.
At birth, babies lack the high-acuity vision needed to see fine details in faces, and face-specific areas of the cortex don’t develop until later. Despite this, babies typically orient and look at faces very early in life, suggesting that another process is at play.
These observations have left scientists with several questions, including: How does the brain move the eyes toward a face to better see fine details? What causes this preference for a face before the brain’s “face areas” develop? And how do the brain’s “face areas” develop the ability to understand faces in the first place?
Krauzlis and his colleagues speculated that the superior colliculus, known for detecting objects, might provide the missing link. Part of the midbrain, it tells the rest of the brain whether something is present somewhere—not what it is, but simply that it is there. It works extremely quickly and connects directly to the motor parts of the brain, directing eye movements toward objects of interest or away from an object in peripheral vision.
To test whether the superior colliculus might help detect faces, co-authors Gongchen Yu and Leor Katz gathered a collection of images, including faces, non-facial biological objects like hands and arms, and other items like fruit or human-made objects. They then showed these images to adult monkeys in the monkeys’ peripheral visual field and recorded the neural responses in the superior colliculus.
Previous studies had suggested that object detection by the superior colliculus was object-independent, meaning that this part of the brain simply noted the presence or absence of something, without distinguishing between what that object might be. However, in this study, Krauzlis and his colleagues found that within 40 milliseconds, more than half of the neurons they measured responded more strongly to images of faces than to other types of objects. Some additional neurons eventually showed preferences for other types of objects, but not until 100 milliseconds. In other words, face-specific detection was much faster than detection of other objects and was preferred by a large proportion of the neurons measured.
The researchers were also able to determine that, although the superior colliculus can receive visual information directly from the eye, this object detection process first requires input from the early part of the visual cortex.
Since the superior colliculus also reconnects to the visual cortex later in the visual processing pathway, scientists suspect that this circuit provides a mechanism for emphasizing the importance of certain objects.
“We think that this face preference circuit may actually support the development of more advanced face recognition processes in the brain,” Krauzlis said. “If that’s the case, deficits in this face preference circuit in the superior colliculus could play a role in autism.”
This study was funded by the NEI Intramural Program. In addition to co-lead authors Yu and Katz, Christian Quaia, Ph.D., and Adam Messinger, Ph.D., also contributed to the research.
This press release describes a basic research discovery. Basic research improves our understanding of human behavior and biology, which is fundamental to advancing new and better ways to prevent, diagnose, and treat disease. Science is an unpredictable and incremental process: every research advance builds on past discoveries, often in unexpected ways. Most clinical advances would not be possible without the insights of fundamental basic research. To learn more about basic research, visit https://www.nih.gov/news-events/basic-research-digital-media-kit.
NEI leads the federal government’s research on the visual system and eye diseases. NEI supports basic science and clinical programs to develop sight-saving treatments and address the unique needs of people with vision loss. For more information, visit https://www.nei.nih.gov.
About the National Institutes of Health (NIH):
NIH, the nation’s health research agency, is comprised of 27 institutes and centers and is part of the U.S. Department of Health and Human Services. NIH is the primary federal agency that conducts and supports basic, clinical, and translational medical research and studies the causes, treatments, and cures for common and rare diseases. For more information about NIH and its programs, visit www.nih.gov.
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The references
Yu G, Katz LN, Quaia C, Messinger A, and Krauzlis RJ. “Short-latency preference for faces in the primate superior colliculus depends on visual cortex.” Neuron. Epub 2024 Jul 2.