My Plastic Brain

by Caroline Williams

  The first test Steve has for me is to work out which one of these strategies I tend to use. He stands me in front of a table that has a 4 x 4 grid of roughly twenty-centimeter squares marked out in yellow tape, and asks me to close my eyes. Then he puts pictures of four objects (for example: a basket, a toy car, an apple, and a typewriter) in some of the squares. I have ten seconds to study the pictures before I close my eyes again while he takes them away. Then Steve asks me to do one of three things. Either a) put them back where they were, b) move to another side of the table and recreate what I saw in front of me, or c) move to another side of the table and put them back in the same squares that they were in the first time. This last one is the hardest, since I need to mentally rotate the table and remember what went where.

  When I think I’ve got the hang of that, he moves the table out of the way to reveal on the carpet a larger-scale version of the grid. This time, I am to do the same task but standing in the middle of the grid rather than on its borders. Sometimes he asks me to recreate the view, other times to put them back in the same squares as before, but with my body facing another direction. Strangely it's even more difficult to do this when I am in the middle of the scene and trying to imagine it from another vantage point—I find myself experiencing the same kind of mental head spin that I got while I was lost in Berlin. I think I can guess which way this result is going to go.

  Then it's off down the corridor to try navigating in a virtual environment. A lot of navigation research is done using adapted video games, and I can’t help wondering if that's why I was considered too old for the London study: teaching the average forty-something to move around in a computer game is like pulling teeth compared with your average twenty-year-old. Poor Steve. I get it in the end, though, and he explains that I will have several tours of the virtual environment (a fairly featureless maze) to learn where various objects are (a wheelie bin, a chair, a fridge, and so on). Once I’ve had a chance to learn those, I’ll be timed to see how quickly I can get to one of the objects from somewhere else in the maze. I later discover that the point of this is to see whether I can hold a map of the maze in my head so that I can take shortcuts from one object to another, or whether I stick to the routes I know. I can guess the answer to this one, too. I know how to get from the wheelie bin to the chair, because that's the route I learned—but free-forming from there to get to the fridge? Forget it.

  Then comes a different kind of virtual-reality game, with a different Steve—post-doctoral researcher Steve Weisberg—who is interested in how and why people's navigation skills vary. This virtual environment looks more like a real place and apparently is based on a real college campus somewhere in America. This time, I have to learn two routes around the campus and memorize four buildings on each. Then I get to learn two more routes that show me how the first two are connected. My task then is to stand at one building and point to where I think one of the others is. It's easy enough when I’m standing in one route and pointing to a building on the same route, but when I have to point to a building on the other route, which involves mentally computing how the two bits of the campus fit together, it feels like a total shot in the dark.

  I’ll have to wait until tomorrow afternoon to find out what all this says about my navigation ability, but I’m starting to get the idea that I’m not a great mental mapmaker. I kind of suspected it already—so I’m intrigued to get into the brain scanner this afternoon and find out if there is a physical reason why that might be.

  SOME BRAIN STUFF: THE BRAIN’S GPS

  I got the basic rundown of the hippocampus and other important brain areas back in Berlin from Klaus Gramann, of the Berlin Institute of Technology. I went to see him the day after picking up the belt from Susan—and it worked great in helping me get there. Gramann's office is in a corner of the city that isn’t easy to get to from Neil and Jess's flat, and I needed to take several trains and buses to get there. The night before, I had studied the map and written directions that made use of the belt—things like “Leave train station and head east on the number M45 bus. Go ten stops and then walk north on Marchstrasse.” I would never normally consider adding compass directions like this, so I’m intrigued to see if it helps.

  As I walk out of the train station, an M45 bus pulls up at the stop next to me. Normally, with ten minutes to go before an appointment and feeling slightly stressed, I’d jump on the first bus that came and hope for the best, banking on having a fifty-fifty chance of going the right way. This time, though, the belt is buzzing on my back so I can instantly tell that this bus is heading west—the wrong direction. I let it go past, cross the road, and wait patiently for a bus going the other way. I am so pleased I want to tell the person in front of me in the line all about it, but my German isn’t up to it. I content myself with a self-satisfied grin and the knowledge that I probably just saved myself a very late and flustered arrival.

  Ten minutes later, when I get off the bus and find myself at a complicated crossroads, I check my notes again. They tell me to head north, so I turn my body until the buzzing is on my belly and stride confidently on. It's so easy! I still arrive a few minutes late but not nearly as late, flustered, and sweaty as I could have been, and so often am. It feels like a whole new world.

  Klaus Gramann looks like a scientist as Hollywood might imagine one to be. He's tall, with artfully graying hair raked into a messy quiff, and the kind of laconic smile that reminds me of someone famous that I can’t quite put my finger on. It later clicks that it's Billy Bob Thornton—he's a dead ringer, right down to the matching goatee. His office, too, looks way cooler than your average scientist’s. A model of a skull, holding a USB cable between its teeth, sits on the desk, next to a bottle of red wine that acts as a paperweight on the obligatory pile of scientific papers. In the corner is what looks like a shrink's couch, overlooked by a skeleton wearing a university lab coat and grinning madly as only a skeleton can. He even has scientific gobbledygook written on the blackboard.

  In less Hollywood style, though, he seems a little stressed about making the English visitor a decent cup of tea. I assure him that the only tea he can find (loose leaves handpicked in the Taiwanese mountains) will be absolutely fine, and that I’m sure it will be delicious even without milk, and then we settle down for a rundown of the brain's onboard navigation system.

  He tells me that the brain areas involved in navigation converge on the hippocampus, but it is far from the only player. This, like so much about the brain, quickly gets complicated, so he cracks open the plastic skull on his desk and pulls out the plastic brain inside, pointing to each bit as he goes.

  In a nutshell, he tells me, the following areas are crucial to finding your way around: first, the parietal cortex, a kind of information hub at the top and back of the brain, integrates incoming information from the eyes, ears, and other senses into a seemingly seamless representation of the environment relative to where you are in it.

  The parietal cortex feeds into the hippocampus, more correctly called the hippocampi, because the brain has a matching pair, each of which is a longish looping structure, buried under the wrinkly outer cortex. The hippocampus and the areas around it are home to specialized neurons that construct a mental map. These neurons are the place cells in the hippocampus, and the grid cells and border cells, which live next door in the entorhinal cortex. Grid cells fire in patterns that give a kind of coordinates system by which we can keep track of the general layout of our surroundings. Border cells help us compute where one thing ends and something else begins, which is always useful if you want to move between them.

  Place cells, though, sound like some kind of computational wizardry that I find difficult to get my head around. They are dotted around the hippocampus, and each is tuned to only fire in a certain location in any given environment. Some of their firing thresholds overlap, so that, as you move through an environment, there is a wave of activity that tells you that you are moving. If you go to a house you’ve never visited before, a c
ertain place cell will spring into action when you are near the sofa, while another fires when you are by the back door. This mapping happens very quickly, and, without us noticing a thing at all, they settle into a firing pattern that allows us to move through the house with no conscious effort. The firing patterns get honed with learning, so the maps get more detailed the more time you spend in a particular place.

  The best thing about these place cells, though, is that they are completely re-mappable, so you don’t need a new one for every place you ever go. The place cell that tells you where your bed is at home might fire by the photocopier at work and by the cheese aisle in the supermarket. They also fire when you recall a memory of those places. Which sounds like it might get confusing if you were thinking about going to bed while standing at the photocopier, but actually it's a bit more complicated than it sounds. It's the particular firing pattern of a cluster of different place cells that means you can tell different places apart in your mind's eye.

  These two bits of information—what your senses are telling you about where things are in relation to you, and what your place and grid cells are telling you about the scene in general—get put together in the retrosplenial cortex (RSC) where another type of neuron, called “heading cells,” compute which way you are facing with relation to the environment. The RSC's main job seems to be to act as a kind of translator that puts you in the picture, so you can move around in an environment efficiently.5

  Finally, there is the occipital place area, at the back of the brain. This has only recently been discovered, so no one knows exactly what it is doing, but it seems to respond more to places than other things like objects or faces.

  When I start to wonder aloud if I might be missing any of these parts, Klaus doesn’t seem terribly convinced. “We all have the same neural basis for all these systems. We have that encoded genetically…. You don’t have to do anything; it's just there,” he says. It's a fair point—despite the fact that, thanks to maps, sat nav, and smartphones, pretty much nobody in modern life uses their navigation skills as nature intended, the gear is still in there, waiting to be used. In fact, we use it every day without even realizing it. People who have a brain injury or stroke in the brain's navigational centers find it impossible to find their way around in everyday life—sometimes even getting lost in their own home. Some people have this problem from birth for reasons that aren’t entirely clear yet. If the system wasn’t working at all, you’d certainly know about it.

  There are definitely differences in how well people use the various bits of kit, though, and Klaus's research largely revolves around finding out why that might be. If you take a group of people to an unfamiliar environment, for example, they use very different strategies to find their way around. “Some people create a survey knowledge from their very first encounter. Some never do. So the question is: why is that? If everybody has the same system, why would there be differences?”

  Klaus tells me that some of these differences are probably genetic: while we all build brains to more or less the same genetic brain-building program, brain regions, like noses and bottoms, come in different shapes and sizes. Some people might come better set up to encode the information in the parietal cortex accurately, for example, which gives the rest of the system a good picture to work with. Some people are also better at keeping track of where their body is in space and how quickly it is moving. Some people come with a larger, or more efficient, hippocampus.

  Then there are the effects of culture—and it's those that interest me most, because they suggest that hacking the system is at least a possibility, whatever genetics has given you. It's also something that Klaus is interested in. “If you grow up in the tundra in northern Scandinavia, it's going to be a totally different environment than growing up in New York City,” he points out. In New York, you might be better off with a landmark- or route-based strategy, for example, but in the tundra you’d need to track the sun or plot your position based on the features of the landscape. And if the strategy you develop as a child in a particular culture works, why would you bother developing the other? Over time, these changes add up to different amounts of gray and white matter in the key navigational areas of the brain.

  These differences seem to start very early. Klaus tells me that in experiments that compared the performance of Dutch and African children on the same sort of grid test that I did in Philadelphia, African children would put the objects back on the grid the way they were with respect to north, south, east, or west, whereas Dutch kids would place them with respect to their own body.

  So could an adult urbanite develop the skills of a desert hunter-gatherer? Perhaps. But it has been found that people who stubbornly use a landmark-based route-learning strategy have less gray matter in their hippocampus than people who use a map-based one.6 There seems to be a trade-off with another part of the brain, the caudate nucleus, which is larger in people who do route-based navigation, and smaller in the mapmakers. But the best navigators of all are those who have a similar volume in both the hippocampus and the caudate nucleus and are able to select the best strategy depending on what the task needs. As with creativity and sustained focus, for navigation skills, building muscle is not the right analogy—again, it all comes down to flexibility.

  Klaus suspects that the difference between strategies comes down to differences in activation in the retrosplenial complex—the translator between mental maps and the sense of where the body is in space. This is very much a work in progress, and although I have been hoping to join in with some of the team's latest experiments, it looks like that isn’t going to happen. One experiment I wanted to try isn’t ready to run, and the other involves walking around a huge hall with a mobile brain activity monitor (EEG) strapped to my back and wearing a virtual-reality headset. It sounds fun, but the hall is being refurbished and won’t be useable for at least six months.

  A month later, over in Philadelphia, though, I get my chance to look at my retrosplenial complex, and other navigational bits and bobs, for clues. It's off to the brain scanner with me.

  The scanner is in another building from the Epstein lab, and while we walk over there, we chat some more about navigation. I ask Russell Epstein, head honcho of the navigation research lab here, if he is one of those scientists who went into a field of psychology to try and explain his own shortcomings. “Actually, I’m pretty good [at navigation],” he replies. “I’ve always been kind of interested in maps.” In fact, he has done a lot to map the brain, too. In 1998, as a young researcher fresh out of his PhD at Massachusetts Institute of Technology, he demonstrated that the brain has an area, called the parahippocampal place area (PPA), that is dedicated to processing scenes rather than objects. It does this, he found, by noticing that there is some kind of three-dimensional structure or geometry to what you are looking at. If you look at a photo of a room, for example, the PPA responds to that as a “place,” but if you cut out the images of the furniture and paste them onto a blank page, the PPA would be less excited about it.

  The PPA is just one of the areas in my brain they are going to look at, along with the hippocampus (to see whether it's as shriveled as I suspect it is) and the occipital place area (OPA), which is a fairly new addition to the navigational circuit diagram.

  First is the structural scan—the bit where they measure my hippocampus and compare it to other women they have scanned in the past (there's no point comparing it to male brains; women's brains are smaller, yet perfectly formed). All I have to do for this part of the scan is lie still and try not to fall asleep. Then comes the functional scan, where they measure which bit of the brain is active while I look at whatever they flash on the screen in front of me. In this case, they show me a mixture of faces, objects, scenes, and scrambled-up images, which appear for a couple of seconds at a time. I later find out that this is so they can find each of the place-sensitive areas, since all three of them—the OPA, PPA, and RSC—respond more strongly to scenes than objects or faces.

 
This kind of imaging, it turns out, is even noisier than a structural scan—it makes a sound somewhere between a pneumatic drill and a fire alarm. Luckily, I have something to do to take my mind off it: I’m told to concentrate on the images and press a button if I see the same picture twice. Afterward, they fess up that this was just a trick to make sure I stayed focused and didn’t drift off. They needn’t have bothered—I don’t feel like attention is so much of an issue anymore. The butterfly seems to be more or less under control, either because of my meditation practice or perhaps because I’m having a fantastic time.

  Just when I’m really starting to enjoy myself, there is one more test, which I later discover is to see how the same three areas respond to large things that might make a good landmark, over small things that are probably less useful. Cruelly, they tell me that there will be a memory test afterward, so I am to remember as many objects as I can. Being a good girl, I do my best to memorize everything I see, only to find out that there wasn’t a test, which means that I filled my memory banks with hundreds of images of staplers, wardrobes, and photocopiers for no reason whatsoever.

  The next day comes the moment of truth: the big results reveal.

  I’m impressed: the team has not only analyzed a huge amount of data overnight, but they have also put together a natty PowerPoint presentation of my results. As I suspected, all of the behavioral tests point toward me using an egocentric strategy: computing where to go based on where things are in relation to my body rather than any kind of mental map.

  In fact, the data suggest that I am borderline incapable of forming mental maps and holding them in my mind for a useful amount of time. In the grid test, for example, while I could recreate the view I had seen from any side of the table, I struggled to put the objects in the same position once I was facing another direction. To me, it felt like the information just slipped out of my head the second I had to use it, a bit like when my mobile phone autorotates when I’m in the middle of reading a sentence, and it takes a while to find where I was. It's disorientating and very annoying.