Kendall (not her real name) decided to ask a neuropsychologist if she had medical grounds for turning down the transfer. He referred her to a neuro-ophthalmology clinic at the University of British Columbia, where a young post-doc from Italy named Giuseppe Iaria was studying the neuroscience of orientation and navigation. After a battery of tests, Iaria concluded that Kendall was perfectly normal. She had average intelligence, memory, and mental imaging abilities, and her brain was completely undamaged. She was simply unable to form a “cognitive map,” the mind’s way of representing spatial relationships. When he put her in a brain scanner and asked her to explore the streets of a computer-generated virtual town, her hippocampus — the brain region responsible for cognitive maps — remained inactive, even though basic memory tests had shown that it was functional. Earlier this year, a paper by Iaria, neuro-ophthalmologist Jason Barton, and their colleagues appeared in the journal Neuropsychologia, describing a new disorder called “developmental topographical disorientation,” or dtd. Kendall was “Patient 1.”
Like any other human trait, navigational skill varies widely — some people crow about their abilities, while others lament their ineptitude. So in a way, Kendall’s condition came as no surprise. (“I was expecting to find someone like that eventually,” Iaria says.) But the brain’s navigational wiring doesn’t just reflect our talent at getting from A to B; it also reflects the ways in which we perceive and interact with the world around us. As our surroundings have evolved over the centuries, so too have our navigational strategies and conceptions, shaped most recently by urbanization and the advent of high-speed travel.
We’re now on the cusp of an even more dramatic change, as we enter the age of the global positioning system, which is well on its way to being a standard feature in every car and on every cellphone. At the same time, neuroscientists are starting to uncover a two-way street: our brains determine how we navigate, but our navigational efforts also shape our brains. The experts are picking up some worrying signs about the changes that will occur as we grow accustomed to the brain-free navigation of the gps era. Once we lose the habit of forming cognitive maps, we may find ourselves becoming more and more like Patient 1.
It was the flower shop that messed me up. I was navigating through the virtual town Iaria had built within a video game platform, trying to learn the locations of four landmarks: a Wendy’s, a Days Inn, a flower shop, and a movie theatre showing Hugh Grant’s Love Actually. It took me three tries to place all of them in the correct positions on a map; typical scores range from two to five. “You’re average,” Iaria (who has since taken a faculty position at the University of Calgary) said cheerfully, crushing my hopes of being a super-outlier. That morning, as I’d walked the three kilometres from my downtown hotel to Vancouver General Hospital, I’d oriented myself by marking the cues provided by an unfamiliar city: glancing at a few key street names I’d jotted on a piece of paper; keeping the mountains on my left once I’d crossed the Granville Street Bridge; and more or less ignoring the shorelines, which seemed to point in different directions every time I looked at the water.
Iaria and McGill University researcher Véronique Bohbot demonstrated in a widely cited 2003 study that our mapping strategies fall into two basic categories. One is a spatial strategy that involves learning the relationships between various landmarks — creating a cognitive map in your head, in other words, that shows where the flower shop and other destinations sit on the street grid. The other is a stimulus-response approach that encodes specific routes by memorizing a series of cues, as in: get off the bus when you see the glass skyscraper, then walk toward the big park. For their study, Iaria and Bohbot created a virtual maze that tested both methods; they found that about half of us prefer spatial strategies, while the other half prefer stimulus-response.
Most of us can use both, depending on the circumstances, but we have a bias toward one or the other. (Kendall was relying solely on cues, in the absence of cognitive mapping skills.) Stimulus-response navigators tend to complete the task more quickly and make fewer errors. “Cognitive mapping is difficult, it’s complicated, it’s tedious,” Bohbot says. The spatial approach does have one major advantage, though: versatility. If I memorize the routes from the flower shop to the movie theatre, and from the movie theatre to the Wendy’s, I can whip back and forth along those routes very quickly. But what if I want to go from the flower shop straight to the Wendy’s? Without a cognitive map, I have no way of figuring out shortcuts or exploring new routes to different destinations. I can only go where my stimulus-driven mind has already left a trail of bread crumbs.
The idea that we carry maps in our heads is relatively new. An experimental psychologist at the University of California, Berkeley, Edward C. Tolman, coined the term “cognitive map” in a 1948 paper showing that rats in certain types of mazes were able to figure out shortcuts to a destination — a clear sign that they weren’t simply learning a sequence of left and right turns. Amazingly, a series of experiments in the 1970s suggested that cognitive maps are more than metaphorical. Certain neurons in the hippocampus, called “place cells,” were observed activating only when the rat was in a specific place. Let the animal wander through a maze, and you could watch a chain of neurons fire in a spatial pattern that exactly matched its path, at a smaller scale.
Whether the same picture can be extended to humans remains a matter of considerable controversy. We don’t know whether the firing patterns of neurons in our hippocampus would trace out the patterns of our neighbourhood, because researchers aren’t allowed to implant arrays of electrodes in our brains. We do know, though, that the human hippocampus stores the same kind of information as the rat hippocampus does, thanks in part to a remarkable series of experiments on a group of truly gifted navigators.
For those of us who have grown up in the reassuring embrace of grid-patterned streets that run straight and don’t change names every two blocks, Old World cities like London — recently declared the most confusing city in the world by a 12,500-person Nokia Maps survey — present huge challenges. So pity the cabbies. Before getting behind the wheel of a black cab, would-be drivers have to pass a test called the Knowledge, which requires them to memorize some 25,000 streets and thousands of landmarks, a task that takes two to four years.
