Two newly identified brain areas reveal how rhesus macaques recognise the difference between intimately familiar faces and faces that the monkeys know less well
Two newly identified brain areas in rhesus monkeys seem to help the animals recognise familiar faces.
Primates, Homo sapiens included, must be able to differentiate between faces and recognise friend from foe because social hierarchies play a large role in daily life. But exactly how primate brains deal with faces is not completely clear.
One idea is that the same parts of the brain are involved in recognising both familiar and unfamiliar faces, just with varying efficiency. But Sofia Landi and Winrich Freiwald at Rockefeller University in New York have now cast doubt on that thinking. Their work shows that distinct brain areas are responsible for recognising the primates you know.
Many researchers have already shown that certain areas of the temporal and prefrontal cortex are involved in unfamiliar face perception in rhesus monkey brains. Using whole-brain fMRI scans of four monkeys, Landi and Freiwald have now identified two additional brain areas that play a role not only in unfamiliar face perception but also in recognising familiar faces.
The two new areas are in the anterior temporal lobe – the part of our brains above and in front of our ears. One is in the perirhinal cortex and one is in the temporal pole. These regions lit up far more when the monkeys recognised a familiar face in a photograph, as opposed to when they were presented with images of a stranger.
Landi then probed the behaviour of the two brain regions in more detail by presenting the monkeys with faces that were either personally familiar or simply visually familiar. It’s the difference between us seeing a picture of our best friend or a picture of a celebrity, says Landi.
She found that the two new areas activated almost 50 per cent more when the monkeys saw personally familiar faces as opposed to visually familiar and unfamiliar ones.
What’s more, when Landi showed the monkeys blurred images of personally familiar faces that then slowly pulled into focus, brain activity in the two newly discovered areas suddenly jumped at the moment the face became sharp enough to recognise – essentially documenting a neural “aha!” moment.
Early in the study of facial recognition, neuroscientists tended to focus on a simple division between familiar and unfamiliar faces, says Claus-Christian Carbon at the University of Bamberg, Germany. “What was missing for a very long time was the essential differentiation between personally familiar and familiar famous faces,” he says.
Carbon and others then began exploring how our brains deal with these two types of familiarity by using doctored versions of famous faces – only to find that we struggle to identify Che Guevara without his iconic beret, for example. It turns out that our recognition of personally familiar faces is very robust to changes in context, like lighting or viewing angle. Carbon says Landi’s work is invaluable, since it helps to explain what is going on in the brain when we view those personally familiar faces.
Landi thinks primate brains are so good at recognising personally familiar faces because of our rich exposure to them. Interacting with familiar faces every day allows us to see them from all angles and under different lighting, and helps us tie them securely to their social context. While Carbon agrees, he also thinks the reason Landi saw different neural signals for recognising visually familiar versus personally familiar faces is because in the latter scenario we have an experience with 3D-heads not just 2D-faces.
Both Landi and Carbon say the next step is trying to replicate the study in humans – although this will present its own challenges because the brain areas involved lie deep within the human brain.
Read more: Who’s the daddy? Ape faces reveal family ties
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