Think of the last time you attended a wedding. You can probably remember the room around you, the place where you sat, the other guests around you and so on. Forming this type of memory depends on the hippocampus, an ancient part of the brain that is buried deep in the temporal lobes, a few centimetres in from your ears. People with damage to the hippocampus are unable to form new long-lasting memories of events and it is also one of the first parts of the brain to be affected in Alzheimer’s Disease. Being able to test abilities that depend on a fully-functioning hippocampus could one day be useful in identifying more serious memory problems that might require further investigation and treatment.
As I explained in a previous post the hippocampus is at the centre of a circuit which keeps track of where we are and which direction we are heading, maintaining a sense of location as we move about and relating our current position to the environment around us. This cognitive map seems to lie at the heart of many spatial abilities, allowing us to find new direct paths between locations and to form new memories of places that don’t depend on our current viewpoint or rely on fleeting surface features of a particular scene. With this in mind, we designed a new task, the Four Mountains Test, to assess people’s ability to recognize places in situations where the viewpoint and surface features change.
The main difficulty with this is devising a test that can’t be solved using visual information that might be stored outside the hippocampus. We used computer generated landscapes where we had complete control over the layout of the environment and could avoid any obvious visual clues. The participant studies a landscape for a few seconds, and then has to identify the same place seen from a different point of view and under different conditions (for example, we change the weather, lighting and vegetation). We found that patients with brain damage affecting the hippocampus but not other brain regions found the task very much harder than healthy people. We also found that patients with Alzheimer’s Disease (and another condition called Mild Cognitive Impairment which sometimes leads on to Alzheimer’s) performed less well than healthy people of the same age and patients with another form of dementia which affects a different part of the brain and requires different treatment.
In the future we hope the Four Mountains test could have some use in identifying patients who can benefit from new treatments for Alzheimer’s Disease. In the next post I describe a more difficult version of the test which we can use to investigate differences in spatial memory in healthy people? Are some people just better at remembering places than others?