What’s in a newborn’s brain? It’s a question we’re obsessed with, because its answers seem to promise us basic truths about what we humans were as a species before our culture became liquid. A book inside Nature Neuroscience this week showed that monkeys raised without exposure to faces did not develop important face recognition sites in their brains. The results help to better understand our own brains, and the research also outlines the concept of how environmental input can lead to specialized brain circuitry over time.
Facial recognition is something that seems to be central to us as social beings. Adult human brains have a circuit dedicated to faces, and even young children seem to look at faces more than other objects in their environment (although these results are disputed by researchers in the field) . Other beginners also prefer to look at the eyes and they have dedicated the brain to take.
As an incredibly social species, are we born with a sense of “face” somewhere in our brains, allowing us to attend to an important part of our environment once we’re out in the world? Some researchers think that this is the best explanation of children’s love for looking at faces. Others think it’s more likely that we develop an idea of what an eye is over time, based on our experience of the world.
To understand how development affects facial recognition in the brain, Michael J. Arcaro, a neurobiologist at Harvard Medical School, led a team of researchers who exposed three baby monkeys to faces. Obviously, this is the best foreign environment for the macaques, which are normally social, so the researchers try to make sure that their life is as normal as possible otherwise. They play with them every day to help with socialization (wear masks to hide their eyes) and make sure the monkeys have interactive toys, soft objects to cuddle, and the smell and sound of other monkeys nearby.
Starting when the monkeys were three months old, the researchers began to compare their growth to four normally grown control monkeys. In the fMRI scans, the control monkeys showed developmentally normal patterns: they had more brain activation when looking at pictures of faces than other objects. The naive monkeys, on the other hand, showed no difference when looking at faces and other objects.
To see if their visual development in general was affected, the researchers also explored whether the captive monkeys were developing other important visual recognition domains. Assuming that these monkeys saw their own hands and the researchers’ hands most of the time, they looked at whether blind monkeys showed greater activation when looking at hands compared to other objects. They do, suggesting that they are developing a hand recognition site. The deficiency, the researchers wrote, was “eye-specific.”
Finally, Arcaro and his colleagues used visual instruments to discover what the monkeys were looking at most in the vast array of images. For everyday things like hammers or clothespins, there is no difference. But when the pictures included faces, the control monkeys focused on them intently, while the gaze-deprived monkeys were more scattered around the picture. In contrast, monkeys without eyes look much more comfortable.
So we are it’s not born with facial recognition?
The results suggest that experience with faces is necessary for accurate face recognition to develop—it is not already present by the time monkeys are born. Past research has shown that monkeys develop similar specializations for whatever they have intensive, early experience with. Arcaro and his colleagues suggest that the results may help to explain how cognitive visual areas develop: if an object is very visible in the environment, infants look at it; the neurons that interpret the stimuli receive an exercise; and eventually the domain is established.
The results, write Arcaro and his colleagues, suggest that “the way babies look is not childlike.” A simple explanation, they suggest, is that newborns have something much more basic in their brains: an innate preference for a particular set of shapes and a bias to see moving objects. Put those oddities in an environment with lots of faces, and facial recognition emerges.
This is not the last word on the subject, and many researchers will disagree on how to interpret the findings. For example, it is possible that baby monkeys come born with some kind of strong preference for looking at the eyes, but their reduction of the eyes causes these features to soften. More research with very young people and infants may help with this question.
There is a danger, when talking about innateness, of using it as a sharp dividing line between “nature” and “nurture.” If there is one thing when we are born, we seem to think that it cannot be changed, a part of our essential nature. If it happens later, we say it to take care of it, and we see it as something that cannot be avoided or that is not so far away from us as a species.
The reality is much more complicated than these binary shortcuts. We are born unable to walk, or talk, or eat solid food, but walking, language and eating are an obvious part of natural human development (inhibitory weakness). And we are born with the beginning of the knowledge of our native language, which we have heard from the inside; but the Spanish language, or the Igbo, are not the remotest parts of the human race.
So facial recognition may still be an accurate, integral part of humans and other primates. But this evidence suggests that the model for what “eyes” are and the preference for looking at eyes requires exposure to a normal environment before they properly develop. And, surprisingly, he suggests a strategy for how that might work.
Nature Neuroscience2017. DOI: 10.1038 / nn.4635 (About DOIs).