22 — Seeing faces is necessary for face-domain formation

Ever since I started studying neuroscience, the ingenuity of the design of experiments to interrogate the secrets of the brain has amazed and humbled me.

This paper is no exception: The authors sought to understand how the facial-recognition system develops in primates — namely, macaques — and if facial recognition and attention is innate (monkeys do it from birth) or learned (monkeys discover that faces are important to attend to). This face patch, a part of inferotemporal cortex that is analogous to the human “fusiform face area”, is known to activate when monkeys look at faces of monkeys, or even at human faces.

If this area exists innately, it’s very interesting to discuss where this came from evolutionarily. And if this area doesn’t exist innately, then it’s even more interesting to discuss: Why does this patch exist in the exact same location in every monkey, and in every human? Why does every monkey (or human) develop facial recognition the same way, if it’s just a byproduct of the way we experience our world?

To explore this idea, the authors raised monkeys in face-deprivation. (In practice, this meant wearing a mask whenever interacting with the monkeys.) To ensure that the only factor under variance was exposure to faces, the experimenters were sure to play with and entertain the monkeys, and the monkeys were kept near other monkeys (but behind a curtain) so that they could hear and smell peers. (To those who, like I was, felt sorry for the monkeys: Don’t worry, after the experiments were over, they joined the social structure of the rest of the monkeys just fine.)

The study found something fascinating: The face patch area of macaque brain just sat mostly still in the face-deprived monkeys. It didn’t adapt to fill some other purpose, but it didn’t go away.

However, it did not develop normally (as you may have been able to guess from the title). Interestingly, the authors found that a neighbor brain area, responsible for the recognition of hands, did develop disproportionately — even stronger was the response of this area to hands in face-deprived monkeys than that in the control population.

The authors surmise that this is likely an adaptation of the monkeys to the next “most expressive” body part after faces in a social setting: Shown pictures of monkeys and humans, the face-deprived monkeys first looked at the hands, and then the rest of the images, while the control population looked at the faces first.

This suggests that the formation of face-domains in primate brain is a response to stimuli in the environment, and, in the absence of face stimuli, monkeys (or humans) will adapt to find other visual “body-recognition” ways of intuiting emotion and identifying individuals.