Scientists have identified a brain circuit in primates that quickly detects faces. This discovery not only sheds light on how primates perceive and identify faces but also has potential implications for understanding conditions such as autism, where face detection and recognition are often compromised from an early age.
Researchers at the National Institutes of Health (NIH) have unveiled a brain circuit in primates that rapidly recognizes faces. This breakthrough elucidates how primates sense and identify faces and could offer insights into conditions like autism, where face detection and recognition are often impaired from childhood. The newly identified circuit initially activates a primitive part of the brain called the superior colliculus, which can then prompt the eyes and head to turn for a better view. This enhanced perspective allows different areas of the brain in the temporal cortex to engage in more intricate facial recognition. The study was published in the journal Neuron.
“Prompt recognition of faces is a crucial skill in humans and other primates,” stated Richard Krauzlis, Ph.D., from NIH’s National Eye Institute (NEI) and the senior author of the study. “This recently discovered circuit elucidates how we can rapidly detect and glance at faces, even when they initially appear in the peripheral visual field where visual sharpness is lacking. This circuit may be what directs attention to faces aiding the brain in learning to recognize individuals and decipher complex facial expressions, thus helping us acquire crucial social interaction skills.”
In adult primates, the brain develops specialized regions in the temporal cortex known as “face patches,” which enable the recognition and differentiation of individuals based on their facial characteristics. However, facial recognition relies on the fine details provided by the eye’s sharp central vision; to recognize a face, we must first directly look at it.
When babies are born, they lack the high acuity vision essential for discerning the fine details of faces, and the cortex’s face-specific areas do not mature until later. Nevertheless, babies typically orient themselves and gaze at faces very early in life, suggesting the involvement of another process.
These observations raised several inquiries, including: how does the brain direct the eyes towards a face for better scrutiny of fine details? What underlies this preference for faces before the development of the brain’s “face patches”? And how do the brain’s “face patches” acquire the ability to interpret faces in the first instance?
Krauzlis and colleagues hypothesized that the superior colliculus, known for object detection, could serve as the missing link. Situated in the midbrain, this structure informs the rest of the brain of the presence of objects without identifying the object itself but merely acknowledging its existence. It operates swiftly and connects directly to the brain’s motor regions, facilitating eye movements towards objects of interest or evasive reactions to objects in the peripheral vision.
To investigate if the superior colliculus might aid in face detection specifically, co-first authors Gongchen Yu, Ph.D., and Leor Katz, Ph.D., curated a range of images, including faces, non-face biological objects like hands and arms, and other items such as fruits or human-made objects. These images were presented to adult monkeys in their peripheral visual field, and neuronal responses in the superior colliculus were recorded.
Prior studies had suggested that object detection by the superior colliculus was agnostic to the object’s identity, merely noting the presence or absence of something without differentiation. However, in this study, Krauzlis and team discovered that within 40 milliseconds, over half of the recorded neurons exhibited a stronger response to face images compared to other objects. While some neurons eventually developed preferences for other objects, this occurred after 100 milliseconds. In essence, face-specific detection occurred much faster than the detection of other objects and was favored by a significant proportion of the neurons examined.
The researchers also found that, although the superior colliculus can directly receive visual input from the eye, this process of object detection necessitates input from the visual cortex’s early stages.
As the superior colliculus later reconnects with the visual cortex in the visual processing pathway, the researchers speculate that this circuit offers a mechanism to emphasize the significance of specific objects.
“We propose that this face-preference circuit might actually drive the development of the brain’s more advanced facial recognition processes,” Krauzlis explained. “If so, deficiencies in this face preference in the superior colliculus could potentially contribute to autism.”
This study received funding from 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.
