The study was published in the June 1 online edition of Nature Neuroscience.
“Our findings provide insight into how we develop a big-picture perspective of the world rather than just an understanding based on the specifics of an individual experience,” says Dr. Blake Richards, lead author of the study, former postdoctoral fellow in Neurosciences & Mental Health at SickKids, and currently assistant professor in Cell and Systems Biology at the University of Toronto. “Essentially, we’ve uncovered how a set of memories change over time, and how the brain over time assembles them into one general memory.”
The study measured how well mice remembered specific experiences compared to a series of multiple experiences, using a water maze experiment. The mice were trained to find a platform in a pool of water. The platform location changed daily, but there were common elements or patterns leading to each location. The researchers found that after a 30-day rest the mice were better at finding the pattern, while after just a one-day delay, they simply looked at the last place they found the platform. Richards explains that this shows that the brain can combine multiple memories over time, even in a resting state, to gain overall perspective.
Richards used the concept of a birthday party to describe how memory patterns help form our knowledge of the world. “As a child, you likely went to many birthday parties. At each party, there were different people, the parties occurred at different times of year and you probably participated in different activities. While we may forget the specific details of these distant memories, the common elements that occurred at each party like presents, cake and candles remain. These common elements form the overall concept of a birthday party in our minds.”
The research team did a second experiment to examine how the brain’s capacity to combine memories affected the ability to learn new information. “We found that when new information was introduced, that did not fit with the old memories, it’s actually learned better,” says Richards. “We can theorize that we learn best when surprised by the information, rather than something that matches what we may have already learned.”
Together, these experiments shed light on the evolution of memories over time and has implications for how the brain generates knowledge and the “big picture” perspective of the world.
This study was supported by grants from the Canadian Institutes of Health Research, a Banting Postdoctoral Fellowship from the Natural Sciences and Engineering Research Council of Canada, and SickKids Foundation.