Onstage at TED, Nancy Kanwisher starts by telling us one of the most surprising results from recent neuroscience discoveries: The brain is not a general-purpose processor, but a collection of specialized components, “collectively building up who we are as human beings and thinkers.”
Imagine, she says, walking into a daycare center and suddenly realizing you can’t recognize any of the children, including your own. This isn’t a strange fantasy. It’s called prosopagnosia, and it happens to people. The really strange thing about it is, in those with that condition, only facial recognition is affected. There are many conditions like this, and Kanwisher say, “these syndromes collectively have suggested for a long time that the brain is divvied up into specific components.”
The effort to identify these components has jumped with the invention of fMRI, functional magnetic resonance imaging. Imaging has been around for a while, but the real advance happened when people discovered how to map activity. When neurons fire, they need more blood. And blood flow is local. So fMRI lets us see what parts of the brain are more active than others.
So, what can you learn from this?
One of her first studies was about face recognition. It was known that prosopagnosia affected a specific region, but was there something special about that region in healthy brains too? She went into a scanner herself, looking at images of faces and objects, for two hours straight. (“As someone who has close to the world record of total number of hours spent in a scanner, I can tell you one of the most important skills for fMRI research is bladder control.”)
The images were primitive by today’s standards, but she found a region with higher activity. Was it a fluke? To test that, she repeated the test many times, and then scanned other people. It turns out almost everyone has a similar face-processing region in a similar part of the brain.
“But what does this region actually do?” Is it really face-recognition? Or does it do other things? Maybe it responds to any body part, or anything human, or anything round. She spent a lot of the next few years testing those hypotheses.
Does that nail it? Nope. Brain imaging can’t tell you if the region is necessary for anything. “Brain imaging can only tell you what regions turn on and off. To tell what part of a brain is necessary for a function, you need to mess with it.”
They did get one chance with an epileptic man. As part of a diagnostic procedure, electrodes were implanted to find the source of his epilepsy, and by chance two electrodes were in the face region. With his consent, they asked him what happened when they stimulated the region. When they did, he reported their face changed — into somebody he’d seen before. “This experiment finally nails the case,” says Kanwisher. “This region is not only selectively involved in facial recognition but causally.”
There are many other specialized parts of the brain. Kanwisher spent a lot of time in the scanner in the past month to show them to the TED audience. She takes us on a visual tour, showing the locations of regions that respond to:
- Regions of space.
- Visual motion.
- Body parts.
- Hearing sounds with pitch (As opposed to sounds w/o pitch).
- Hearing sounds without pitch.
Are there specialized regions for complex processes? She says yes, including regions for:
- Language. A very specific part: understanding the meaning of a sentence.
- When you’re understanding what another person is thinking, “the most amazing region we’ve found so far.”
There are probably more to be discovered. “But importantly,” she said, “I don’t think we have specializations in the brain for every important mental function.”
A few years ago a scientist in her lab thought he had found a special region for detecting food, which would be important for survival. But then he designed the crucial experiment to test that hypothesis. It turns out it wasn’t about food, but colors and shapes. Again, not every process has a specific place in the brain.
So, how do we process all the other information? “In addition to these highly specialized components, we also have a lot of general-purpose machinery.” They have found certain regions that seem to be engaged with any difficult task at all.
Kanwisher also points out that these regions are present in pretty much any normal brain in pretty much the same region — they are part of the fundamental machinery. It didn’t have to be this way: “The brain could have been more like a kitchen knife than a Swiss Army knife.” Instead we have a complex and rich picture of general-purpose components as well as highly specialized components.
It’s still very much the early days of this kind of work, she says: “The most fundamental questions remain unanswered.” For example:
- What do these regions do?
- Why do we need several face regions?
- How do they divide tasks?
- How are they connected?
- How does this very systematic structure get built? In an individual’s development and through human evolution?
She closes by talking about the high cost of neuroscience research, and noting that many people justify it based on the promise of cures. Of course that’s important, she says, but, “This is worth doing even if it never led to treatment for another disease. What could be more thrilling than to understand the fundamental mechanisms that underly human experience, who we are? This is, I think, the greatest scientific quest of all time.”