Know Your Brain: Crossing Wires — The Fusiform Face Area

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How often have you heard “Don’t I know you from somewhere?” or at the very least, thought that thought? You’re out shopping or driving and suddenly you see someone who looks familiar. The same probably happens if you’re watching a movie or TV show and an actor you’ve seen in something else appears on the screen and you’re trying to put a face to a name — sometimes the name comes to mind right away, or sometimes you need a friend to blurt the name out. When this happens, it’s due to the functioning of your brain’s fusiform gyrus, located at the base of the brain.

While the fusiform gyrus is crucial in facial recognition, its other functions are still being understood. It makes up the largest macro-anatomical structure found inside the brain’s ventral temporal cortex, which provides structures used for high-level vision, the ability to look at an image and translate its features into recognizable patterns. The name fusiform refers to the fact that the gyrus here takes on a spindle-shape that is wider at the center than at either of its ends. If you’ve been wondering what gyri are — you need only look at a picture of the human brain. Gyri are those folded up wrinkles all around the brain that give it its distinct shape.

The fusiform gyrus is found at the basal surface of the brain’s temporal and occipital lobes, where its boundaries are defined by both the collateral sulcus and the occipitotemporal sulcus, respectively. The temporal lobe is crucial for the processes of visual memory as well as language processing and emotional recognition, which is why the fusiform gyrus is thought to be the reason we recognize words in a book and can form mental images in our heads as we read, while the occipital lobe determines the spatial orientation and denotes the color of every image we come across as the brain takes in visual information.

Where It Gets Complicated

It was Dr. V.S. Ramachandran, a neuroscientist working with scientists from the Salk Institute for Biological Studies, that uncovered a pathway between the fusiform gyrus and the angular gyrus in the brain back in 2003. The fusiform gyrus takes shape information and then relays it to the angular gyrus which uses an array of higher density fibers to process color, a phenomenon known as grapheme-color synesthesia that causes us to associate colors with the shapes of numbers and letters. In some people, this wire-crossing can cause even more bizarre extremes: individuals who report tasting numbers or hearing vibrations from different colors.

While facial recognition and word recognition are two of the characteristics we now associate with the fusiform gyrus, there are also the complications associated with these aspects that may have their source in the macro-structure as well, such as the disorder prosopagnosia, or face blindness, in which it is difficult to recognize familiar faces despite other aspects of an individual’s vision remaining intact. The complications of dyslexia, in which word recognition is difficult despite otherwise ordinary vision, may also have its roots in problems with the fusiform gyrus.

You may wonder what is unique about these disorders from any other type of visual impairment, and the key lies somewhere near the base of the skull — a small section of the brain that neuroscientists refer to as the fusiform face area (FFA), which specializes in processing faces.

Dr. Nancy Kanwisher, the MIT-based neuroscientist credited with identifying this structure two decades ago, along with her colleagues recently made a new discovery, published in the Proceedings of the National Academy of Sciences. The researchers found that even people who were born blind have a fusiform face area that remains active. Even if you’ve never actually seen a human face in your life, your brain processes and assigns “faces” to the people you talk to. The team of researchers noticed that even in blind participants, the fusiform brain area became active when they touched a three-dimensional model of a face.

“That doesn’t mean that visual input doesn’t play a role in sighted subjects — it probably does,” says Kanwisher. “What we showed here is that visual input is not necessary to develop this particular patch, in the same location, with the same selectivity for faces. That was pretty astonishing.”

Never Forgetting A Face

A study on people who were born blind gave Kanwisher and her team of researchers the opportunity to evaluate long-standing questions about how sensory specialization has developed in the human brain. In this particular instance, her team looked at face perception, but there are myriad unanswered questions about other aspects of human perception.

“This is part of a broader question that scientists and philosophers have been asking themselves for hundreds of years, about where the structure of the mind and brain comes from,” she says. “To what extent are we products of experience, and to what extent do we have built-in structure? This is a version of that question asking about the particular role of visual experience in constructing the face area.”

Kanwisher’s work explores some questions proposed in a study from researchers in Belgium and the Netherlands that was published in the Proceedings of the National Academy of Sciences. In this study, congenitally blind subjects were scanned by functional MRI technology while listening to an array of different sounds — those we would associate with faces, like laughing and chewing, and others that we would not. The previous study recorded higher activity in the FFA to face-related sounds than to noises like a ball bouncing or hands applauding.

Sensing A Pattern

The MIT researchers also looked into several conflicting hypotheses explaining how our sense of face-selectivity consistently develops in one particular brain region. A common proposal is that our FFA develops its ability due to visual input coming from the fovea (the center of the retina), and we focus on the faces at the center of our field of vision, one that doesn’t hold up to scrutiny following this new research.

It has also been proposed that the brain’s FFA tends to prefer curved shapes, something the MIT researchers also couldn’t find evidence of when they asked their blind participants to handle both eggs and cubes. A third hypothesis, and one that Kanwisher’s team found support for, suggests that the FFA processes faces due to its connectivity to other parts of the brain. First, they studied what is known as the FFA’s connectivity fingerprint — weighing the processing activity coming from the FFA against other activity taking place in the brain. Afterward, they found that a model replicating the typical wiring of the FFA and its pathways to neighboring brain regions could be used to predict the brain’s response to faces in both blind and sighted subjects. They also found that strong connections to the brain’s frontal and parietal lobes could be the most crucial in determining how active the brain’s FFA will be.

“It’s suggestive of this very interesting story that the brain wires itself up in development not just by taking perceptual information and doing statistics on the input and allocating patches of brain, according to some kind of broadly agnostic statistical procedure,” Kanwisher says. “Rather, there are endogenous constraints in the brain present at birth, in this case, in the form of connections to higher-level brain regions, and these connections are perhaps playing a causal role in its development.” It would seem that being social by nature is something that’s long been hardwired in our evolution and this specific region is yet another piece of the puzzle.

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