Picture an in depth friend. Imagine their face, the sound of their voice, their height, what they normally wear. You is perhaps surprised to learn you’ve gotten just used a bunch of various brain regions to recall this information.
Curiously, there isn’t a single brain region that’s involved in representing the people we all know. Seeing a friend’s face or hearing their voice prompts different parts of the brain. This is since the brain is modular. It is made up of various regions that perform specific tasks.
The modular brain
The most striking example of modularity is the face perception network. Faces selectively activate a sequence of distinct brain regions spanning the occipital and temporal lobes. Damage to this network profoundly impairs face recognition abilities, a condition called prosopagnosia.
An analogous network of face regions can also be present in monkeys and apes suggesting that a modular face network is an evolutionary adaptation. Possessing dedicated face processing hardware likely allowed us to quickly discern friend from foe, and such rapid identification would undeniably have helped our ancestors deal with the pressures of living in social groups.
Although vital, faces usually are not the one source of data we use to discover people. It is feasible to recognise someone just by hearing their voice. Indeed, patients with damage to their face processing network can still recognise people from the sound of their voice or the best way they dress.
However, there isn’t a single brain network involved in analysing identity. Voices are processed by an area positioned within the auditory cortex, and body areas are anatomically distinct from regions that process faces. So how does the brain mix these different physical cues to generate the sense of a novel individual?
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Putting all of it together
Consider a comedian imitating a politician. Comedians can evoke a robust sense of one other person’s identity, even after they lack a transparent physical resemblance to the person being imitated. Likewise, actors can create a various range of characters just by changing their voice, posture and the way they move.
If the regions that process faces, bodies and voices are anatomically distinct, then how is our unified sense of one other person’s identity formed? How do these different networks communicate with one another?
We recently explored this query in a brain imaging study that examined the spatial organisation of face and body networks. We used magnetic resonance imaging (MRI) to record brain activity while participants viewed images of faces, bodies and customary household objects. We examined brain responses in two face areas, one in a region related to memory and one other in a region involved in vision.
In the visual region, responses to faces and bodies showed a modular organisation. We found that face and body selective areas were spatially distinct from one another. However, within the memory region, face and body selective responses were similarly organised, so areas that preferred faces also showed a preference for bodies.
A gaggle of MIT researchers who examined the brains of monkeys found similar results. In this study, monkeys were shown pictures of faces, headless bodies and pictures of whole bodies with the faces intact.
The results showed that the face area in the identical memory region preferred images of whole bodies in comparison with either faces or bodies alone. Importantly, the response to whole bodies was greater than the combined response to isolated faces and bodies.
The binding power of memory
Together, these studies show that information from the face and body networks converge in parts of the brain that form memories. Previously, it was understood that these memory regions were related to knowing whether a face was familiar.
This latest evidence tells us that memory regions are also chargeable for binding together different perceptual cues to create holistic, integrated representations of the people we encounter.
These findings illustrate how the brain uses different organisational schemes to assist us understand our social world. A modular organisation affords fast, efficient extraction of vital information concerning the people around us.
However, the brain must also bind the output from these various systems together to maintain track of all different people we interact with. Doing so helps us organise the complex web of friends, family, colleagues, Facebook acquaintances, public figures and celebrities that populate our increasingly social world.