We continually rely on our abilities of spatial navigation, be it for the daily commute to work, a trip to the local supermarket, or simply to make our way to the bathroom in the middle of the night. These tasks involve complex cognitive processes, yet most people perform them effortlessly and some develop them to a remarkable degree. Take, for example, London taxi drivers, who have a highly detailed knowledge of the 25,000 streets that lie within a six-mile radius of Charing Cross station, as well as the locations of thousands of “points”, or landmarks, such as nightclubs, hospitals, hotels, theatres, railway and police stations, places of worship, parks and government, historical and public buildings.
Because most of us make little or no conscious effort to navigate our environment, we find it difficult to imagine being unable to do so. But there are numerous reports of people who have impaired spatial navigation. Such deficits are associated with damage to the various parts of the brain involved in attention, perception or memory, which can occur as a result of traumatic brain injury, epilepsy or Alzheimer’s Disease. Now researchers from the Brain Research Center at the University of British Columbia report the case of a woman who has never been able to orient in her environment, even in the absence of any apparent brain damage. The study, published in the journal Neuropsychologia, is the first documented case of what the researchers have named developmental topographagnosia (or topographical disorientation).
When one navigates through a novel environment, the brain generates cognitive maps of the new surroundings. The idea of a cognitive map dates back to a seminal 1948 paper by the psychologist Edward Tolman. Based on his experiments in which rats were taught their way through a maze, Tolman concluded that “in the course of learning something like a field map of the environment gets established in the rat’s brain,” and that “incoming impulses are usually worked over and elaborated…into a tentative, cognitive-like map of the environment… indicating routes and paths and environmental relationships.”
We now know that Tolman’s cognitive maps are generated by the hippocampus and surrounding temporal lobe structures, which are crucial for the spatial memory which is required for navigation. Lesions in the hippocampal formation often lead to a disorder known as anterograde disorientation, in which the ability to learn new routes is impaired. But navigation involves more than just spatial memory, and engages a diffuse network of regions distributed throughout the brain. For example, patients with lesions in the retrosplenial cortex near the boundary between the parietal and occipital lobes are unable to obtain directional information from landmarks; those with damage to the fusiform gyrus, found at the junction between the occipital and temporal lobes, are unable to recognize the landmarks themselves; and those with damage to regions toward the back of the parietal cortex cannot determine the position of landmarks relative to themselves.
The new case study is of a 43-year-old left-handed woman known as Patient 1 (Pt1). According to her parents, her language and cognitive development were normal but has never been able to navigate. From about the age of 6, she recalls panicking at the grocery store whenever her mother disappeasred from sight. She completed high school successfully, but for the entire 12 years of her schooling had to be taken to and from school by her sisters or parents. Each time she tried to leave home by herslef, she got lost, and so relied on friends to accompany her wherever she went.
The woman now lives with her father and is employed as a public servant. She has no difficulty discriminating left from right and easily recognizes familiar places and landmarks. But she follows a streotyped route to get to the office where she has worked for 5 years – every day, she takes the same bus dowtown and knows where to get off because she recognizes a distinctive square; from there, she follows a straight 30 meter route to her office block. To get home, she follows exactly the same route in the reverse direction, but gets lost with even the smallest deviation from that route; she also often gets lost in her neighbourhood and has to call her father to ask him to get her.
After being told that her office would be relocating, Pt1 sought help and was eventually referred to neuropsychologist Giuseppe Iaria and his colleagues at the University of Columbia’s Human Vision and Eye Movement Laboratory. Here, she took part in a series of detailed investigations, including functional magnetic resonance imaging (fMRI), neuropsychological evaluations designed to test general intelligence, memory and visuospatial abilities and various assessments of her navigational skills. Her performance on these tests was compared to that of a control group consisting of four left-handed females.
Pt1 was found to be fluent and to have normal verbal understanding. Her short- and long-term memory were also found to be normal; she showed no signs of deficits in attention or perception and scored just below average on an IQ test. Neuroimaging did not reveal any signs of haemorrhage or ischemia, and no structural abnormalities were detected in the hippocampal formation or any other part of the brain.
To further examine Pt1’s navigational skills, Iaria and his colleagues administered a series of real-world tests performed in a part of the city that was unfamiliar to her, which aimed to assess the strategies she uses to orient herself. In one of these tests, she was asked to follow a researcher from one place to a target location and was then led back to the starting point via a different route. She was then asked to return along the original route to the target location. In a similar test, the researcher indicated during the initial phase various landmarks located at crossings.
Pt1 performed both of these tests accurately. During the test phase on the first one, she named the buildings she was looking at whilst navigating and later confirmed that she was using the buildings and landmarks rather than referring to the signs showing the names of the streets. Thus she was able to learn a path which she had previously travelled and to navigate it successfully. The patient also had no difficulty in navigating a route using a list of instructions given to her by the researchers.
When given a map to navigate, however, she ran into problems. One of the map-based navigation tasks, she did not take the shortest possible route to the specified destination, and made a wrong turning on the way. When asked to draw a floor plan of the house in which she lived, Pt1 produced a map (above left) containing the correct number of rooms in their proper sequence. However, although she could tell the researchers where various objects could be found in the house, she was unable to locate any of them on her plan. When her map was compared to one produced by her father (above right), it became clear that Pt1’s map was greatly distorted and had an inaccurate scale.
Similar results were obtained when she was asked to draw a map of her route to work. However, when she was asked to produce maps of unfamiliar places, such as the main routes of the city or her neighbourhood, she was unable to, and stated that she did not have “in my mind a map to report”. Thus, it appears that although Pt1 can create approximate representations of environments with which she is very familiar, based on the procedures she had learnt to navigate them, she has a selective difficulty in forming spatial representations of less familiar environments.
To test this possibility, the researchers administered several tests which assessed Pt1’s ability to form and use cognitive maps in a virtual city. Created using the editor of a three-dimensional gaming software, the city consisted of several buildings of different shapes and sizes and four clearly identifiable landmarks (a cinema, a restaurant, a hotel and a flower shop). In one task, the patient was asked to navigate freely through the virtual city and to learn the locations of the landmarks, and their spatial relationships, as she did so. In the second, she was required to draw upon her mental representation of the virtual city to find the shortest possible route to reach the location of one of the landmarks.
Pt1 performed significantly worse on these tests than did the controls. It took her more than 30 minutes to form a cognitive map of the virtual environment, compared to an average of 11 minutes for the controls. Her exploration of the environment invovled covering the same route over and over again and she later reported that instead of devising a specific strategy she was trying to remember the locations of the landmarks with respect to one another. She said that she had difficulty remembering where the landmarks were in relation to her location; each time she encountered another landmark, she got lost. Likewise, Pt1 took significantly longer than the controls to find specific landmarks. On average, it took her 75 seconds to do so, compared to an average of around 16 seconds for the controls. However, it was found that she could learn and use a cognitive map of a simplified environment after intensive training.
Finally, the researchers used fMRI to assess the pattern of activation in Pt1’s brain as she navigated through the same virtual city. Her results were compared to those of 9 healthy controls who had performed exactly the same tasks during a previous study. As Pt1 formed a map of the virtual city, significant increases in neural activity were observed in distributed regions of the frontal, temporal and parietal lobes. Exactly the same pattern was found in the healthy controls. However, unlike the controls, the patient showed no increase in activity of the hippocampus or retrosplenial cortex, the two regions which are known to be critical in cognitive map formation.
There is an important difference between this case and those of patients with navigation deficits as a result of brain damage. The latter often have other cognitive impairments, such as attention or memory deficits, which makes it difficult to determine exactly which process is being disrupted. Pt1, on the other hand, has a highly selective disorder which apparently results in an inability to form cognitive maps. Actually, she was not completely incapable of this task. One week after she first took the virtual city tests, Pt1 started a training program consisting of six one-hour sessions per week. Afterwards, the time it took her to form a map of the same virtual city was reduced to 5 minutes, and the time taken to find a specific landmark to just 4 seconds.
Surprisingly though, the patient appears not to have attempted to form such maps of her home or of her route to and from work. Rather, she seems to have adopted a life-long strategy which minimizes her need to form maps, because she has great difficulty doing so. This may provide clues to the origin of her disorder. In the now infamous studies of London taxi drivers, Eleanor Maguire and her colleagues showed that there is a strong correlation between the size of the hippocampus and the amount of experience in the job – the longer one has been driving a taxi, the larger is their hippocampus. It therefore seems plausible that a reluctance to form cognitive maps, starting from an early age and continuing throughout life, could result in a reduced capacity for the hippocampus to perform this particular function.
Iaria and his colleagues note that firm conclusions should not be drawn from neuroimaging studies involving just one participant. But they also suggest that the imaging data are useful, because small increases in hippocampal activity were detected following the intensive training sessions. The researchers believe that there are likely to be more people with developmental topographical disorientation, and have created a website called website in the hope of finding them and gaining a better understanding of the disorder.
Reference: Iaria, G. et al (2008). Developmental topographical disorientation: Case one. Neuropsychologia, DOI: 10.1016/j.neuropsychologia.2008.08.021 [PDF]