How we learn the differences between two similar locations and why it sometimes goes wrong has been explained in a recent study on holistic retrieval.
Every day, we complete tasks and travel the same routes, exactly as we have done previously. Often an entire morning commute can pass without your brain really departing from the autopilot setting, while it focusses on more important matters such as which seating plan will lead to the least friction at family Thanksgiving.
This is a key function of your brain that allows you to pass through these situations without relearning the same information each day, allowing you to instantly recall that the eggs are next to the bread in your local supermarket without breaking a stride. This specific location-associated recall is referred to as holistic retrieval.
However, every now and then something jolts you away from thoughts of last holiday season and cousin Jack and aunt Jill’s fateful sense of humour. You realise that you have not, in fact, turned in to the freezer isle of your local supermarket – just round the corner from the milk – but are instead staring at a row of pastries in a similar store, with a slightly different layout. Suddenly it all begins to feel very alien – your holistic retrieval has tricked you – and you become alert, ready to decipher your new environment.
These instances are relatively rare; however, researchers have been interested in how the brain typically establishes differences between two otherwise similar spatial environments. A team of researchers, led by Li Zheng (University of Arizona, AZ, USA), recently set out to answer this question using complex memory tests. Their findings could have implications for the study of Alzheimer’s and our fundamental understanding of spatial memory.
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To do this Zheng created an animated video of someone passing through three different virtual ‘Cities’. Each city was largely identical but with a few key differences relating to a sequence of stores, some of which were the same in each city and some of which were different. 27 participants were asked to memorize the location of each store in each city and were then tested on the cities’ layouts.
Participants with a score above 80% then repeated the test whilst inside an MRI scanner, allowing researchers to examine the active areas of the participants brain during the test.
When asked about most aspects of the cities, the brain activity patterns observed were similar. However, when asked about stores that appeared in all three cities the observed brain activity varied to a surprising degree. This suggests that the brain reacts differently to situations that are very similar but do have a key difference, in order to overcome typical holistic retrieval and to make the effort to learn new information. The researchers termed this phenomenon ‘repulsion’ and believe our brains use it to ensure that during quotidian situations with a key point of difference we learn from the experience.
The key areas of activity in the brain highlighted were in the prefrontal cortex, which is known to control functions including decision making and planning, reinforcing the theory that this region stores information regarding the similarities between two environments.
Explaining the potential relevance for these findings for Alzheimer’s, senior author Arne Ekstrom stated that, “the implications here would be maybe this neural repulsion mechanism is something that could be impaired with aging. If you understand the mechanisms whereby healthy, young brains work, maybe you can better understand some of the things that go wrong with neural disease and aging.”
Next, the team want to explore these findings further in relation to neural diseases, learning how these systems are affected in people with Alzheimer’s