When I moved to Montreal, it took me a while to get oriented. After a few weeks of constantly checking Google Maps, I developed a mental image of key landmarks and how to navigate between them. I can now get to Jean-Talon market from Mont-Royal, or to 捆绑SM社区 campus from the Lachine Canal because I understand where these places are in relation to each other. This feeling of being lost and disoriented but eventually gathering our bearings is nearly universal. Nearly universal, because there is a small number of people who remain in the 鈥榣ost and disoriented鈥� stage their entire lives, no matter how long they鈥檝e lived in a location. This condition is called Developmental Topographical Disorientation (DTD).
From insects to mammals, navigation is essential for a species' survival. Bees remember the distance and direction of pollen-rich flowers, then communicate that information to their colleagues using a special . Squirrels find their months after they are buried using detailed mental maps and landmarks. must pass a rigorous qualifying exam that requires near-perfect memory of all possible routes through the city. When we are surrounded by extraordinary examples of how organisms navigate, it鈥檚 easy to take for granted the complexity behind plotting a route from point A to point B. People with DTD are a stark exception. Learning about individuals with this disorder helps us understand if we really do have a map in our minds and, if so, where it is located.
Always Lost
One person with DTD described the condition as despite being in familiar locations such as their neighbourhood, route to work, or in certain cases, their own home. Like most neuropsychological disorders, the severity of DTD varies from person to person and can sometimes be accompanied by problems with memory or focus.
The of DTD was in a middle-aged Canadian woman. Every morning, she followed a strict and explicit set of instructions to get to her office. Take the bus, get off when she sees a certain landmark, and walk 30 metres to her office building. While she generally managed to get to work independently, she sometimes got disoriented on her way home and needed her father to pick her up. And if asked to take a route other than from home to work, she would be completely lost. When she learned that her office building was moving, which would cause months of disorientation, she sought professional help. Perhaps a neuropsychologist could help her understand this disorder and offer solutions.
, a neuropsychologist currently at the University of Calgary, gave this woman a series of tests designed to find what areas of navigation she struggled with. While it may seem simple on the surface, navigation is a complex task that involves many sensory and cognitive processes. First, we must be able to recognize our current surroundings, then remember these surroundings, understand where one destination is relative to another, plan a route, and finally update our plan in case we encounter a roadblock (literally or figuratively).
On some of the tests Dr. Iaria administered, the patient performed normally: she could copy a route after seeing an examiner complete it, identify landmarks, and follow verbal instructions to reach a destination. Where she did struggle was in creating a cognitive map of the environment. Dr. Iaria gave participants a two-phase assessment designed to quantify how well someone can form and use a cognitive map. In the first stage, or the 鈥榣earning鈥� stage, participants freely explored a simplified virtual environment. Once the participant felt comfortable, they were tested by drawing a map of the virtual environment. If they drew an incorrect map, they were allowed to explore more until they could draw a correct map. This entire process 鈥� the exploring, assessment, and potential re-entry into the exploring phase 鈥� was timed and compared between participants. In the second stage, or the 鈥榰sage鈥� stage, participants were given a series of destinations to which they had to navigate by the shortest route possible. The experimenter timed how long the participant took to figure out and complete each route.
In both phases of this assessment, the woman with DTD performed worse than control participants. She took three times longer to explore and correctly draw a map of the virtual environment and took significantly longer to figure out each test route. This shows that she struggled both to create a cognitive map and use it to navigate. Such a finding isn鈥檛 limited to one patient either; can鈥檛 form a cognitive map. Does this mean that humans really do have a map in their brains, and if so, can its location be found?
Not Quite Google Maps
Cognitive maps are not the same as the map in your car's glove compartment or the map you can load on your phone. These maps accurately show the distance between streets and buildings and don鈥檛 give special treatment to emotionally significant landmarks (like a childhood favourite ice cream shop). Instead, the map in our mind is . The map is egocentric (鈥渟elf-center鈥� in Latin) because we place ourselves at the center of the world and recall where landmarks are relative to us. The map is flexible because we constantly update it to absorb or eliminate destinations. For example, when I found a new favourite caf茅, it joined the roster of 鈥榙estinations鈥� in this cognitive map. It鈥檚 important to note that scientists still aren鈥檛 sure of the exact shape this map takes 鈥� 鈥榚gocentric and flexible鈥� is simply a starting place to describe a complicated thing. Trying to locate this cognitive map, one we still don鈥檛 completely understand, is another challenge.
Many parts of the brain show activity when we navigate, and scientists are investigating nearly all of them. Two such brain areas that are especially active when humans are doing spatial tasks are the hippocampus, a seahorse-shaped region buried under layers of brain tissue, and the retrosplenial cortex, a section of the brain located approximately underneath the crown of your skull. In studies of individuals with DTD, scientists haven鈥檛 noticed any significant differences in the size or shape of the hippocampus or retrosplenial cortex. However, they did notice a difference in how . In patients with DTD, activity in the hippocampus is less likely to be followed by activity in the retrosplenial cortex and vice versa. Neuroscientists refer to this as 鈥榝unctional connectivity鈥� or synchronizing activity between different brain areas. This finding suggests that how these brain areas talk to each other, not just what each brain area is made of, is essential for human navigation.
While research on people with DTD didn鈥檛 unlock the discovery of a new 鈥榥avigation鈥� area of the brain, it did teach us an important lesson about how our mind works. Next time you successfully arrive at a destination, you may want to think twice about your hippocampus, retrosplenial cortex and, perhaps most importantly, all the connections between the two.
Maya McKeown recently graduated from 捆绑SM社区 with a Bachelors of Science (BSc) in Neuroscience and a minor in Mathematics.
