Recognizing faces is a skill that humans and primates both have. When it comes to human infants, they tend to focus their gaze on faces. They do this before their eyes develop the ability to discern the features of a face and before the face-specific area of temporal cortex of the brain is fully developed. What leads to such an early adoption of this skill, and where in the brain does it happen? As always, research sheds light on this important ability.
Scientists at the National Institutes of Health (NIH), knew that in adult primates, the brain has specialized regions of the temporal cortex known as “face patches”. These patches enable the ability to recognize individuals by their facial features. Of course, facial recognition depends on directly looking at the face in question, which is where the eye’s high-acuity central vision comes in.
Researchers wanted to understand three things:
1. How does the brain direct the gaze of the eyes towards a face to discern fine details?
2. What leads to the face preference before the “face patches” develop?
3. How do the “face patches” develop the capability to perceive faces in the first place?
Researchers guessed that the part of the brain known as the superior colliculus, which detects objects, might provide some answers. The superior colliculus is part of the midbrain and signals to the rest of the brain if something is present, without identifying the object. It works quickly and connects to the motor parts of the brain, directing the movement of the eyes toward object of interest.
To test if the superior colliculus aids in face detection, scientists compiled a collection of images, including faces, hands, arms and other items, such as fruits or human-made objects. These images were shown to adult monkeys in their peripheral visual field. The responses of the neurons in the monkeys’ superior colliculus were recorded. Scientists found that within 40 milliseconds, more than half the neurons measured responded more intensely to images of faces than other objects. The superior colliculus reconnects back to the visual cortex later in the visual processing pathway, so scientists think that this mechanism helps the brain prioritize certain objects, possibly driving the development of facial recognition processes. In fact, it may even drive the development of the brain’s facial recognition process.
Since the brain recognizes faces more quickly than other objects, the next question arises: Are certain faces given more value than others? Researchers at the University of Tsukuba in Japan explored this question, as well.
As babies grow, remembering the faces of caregivers is essential for survival. One part of the brain, namely the striatum tail of the basal ganglia, plays a crucial role in associating value to objects through long-term experience. However, how it functions in daily life wasn’t well understood.
As expected, scientist wanted to learn how this works. They presented monkeys with familiar and unfamiliar images, and recorded the neural activity in the striatum tail. They found that the mechanism for storing memories of familiar faces was the same as that used for remembering the value of objects. They also showed the monkeys photos of familiar caregivers and strangers, and recorded the neural activity from the striatum tail. Another part of the brain, the caudate nucleus, located below the cerebral cortex, responded strongly to familiar faces and weakly to unfamiliar ones. Additionally, the same neurons responded similarly to objects of varied value. Since these neurons are involved in the quick identification of valuable objects, they may help children quickly identify familiar individuals. This work revealed the mechanisms that allow the brain to form and maintain social relationships.
Recognizing faces is a skill that humans developed for their survival. After all, they could end up in trouble if they didn’t know who was “friend” and who was “foe”. The neural mechanisms involved in this skill aren’t limited to facial recognition; they also wire the brain to differentiate people from objects, aiding spatial navigation. Something to think about the next time you see someone and think “Do I know this person from somewhere?”
https://www.tsukuba.ac.jp/en/research-news/20240611140000.html
https://neuroscientificallychallenged.com/posts/know-your-brain-caudate-nucleus