How does the Brain Distinguish Between Old and New? It is Biased.

Last weekend, I went to a cinema in the USA for the first time. I was conscious of two things—taking in the cine-going experience in a new country, and reminiscing about the last time I was at a theatre with my friends a year ago.

Is This Memory Already Stored Inside Me?

When we come across a situation, there are two conflicting processes that can take place- a new memory can be formed, or an old memory can be retrieved. Both these processes involve a common region of the brain called the hippocampus. However, despite the effortlessness with which we form memories and simultaneously recall old ones, the two processes themselves involve very different networks. Recalling a memory involves maximizing overlap with existing memories. On the contrary, forming a new memory involves minimizing the overlap with other memories. These are two conflicting requirements; how, then, does the brain decide what to do?

Recent experiments by researchers at Columbia University and New York University are showing that this decision is influenced by incidents prior to the decision. That is, prior incidents bias our brain either towards forming a new memory or towards recalling an existing one.

The brain is not very objective in its decision making. [Image Credit: Wikimedia Commons]
Participants were presented with pictures of novel and familiar objects and asked to classify them into one of three classes— identical, different, or similar but not identical to a previously encountered object. The ‘test’ objects were very similar to previous objects, but had subtle differences. It was found that participants who had been primed with a series of new objects tended to classify these as not identical, whereas participants who had been primed with familiar objects tended to classify them as identical. In another experiment, participants were found to form links between overlapping memories better if these overlapping memories had been formed after a retrieval of a memory, and their ability to form links between memories was less if the memories had been formed after a new memory had been formed. That is, a preceding experience definitely affects how a memory is stored in the brain with respect to other memories.

Biased by Our Environment

“We’ve all had the experience of seeing an unexpected familiar face as we walk down the street and much work has been done to understand how it is that we can come to recognize these unexpected events,” said Lila Davachi, an associate professor in NYU’s Department of Psychology and the study’s senior author. “However, what has never been appreciated is that simply seeing that face can have a substantial impact on your future state of mind and can allow you, for example, to notice the new café that just opened on the corner or the new flowers in the garden down the street.”
This is behavioral evidence that memory encoding and retrieval can evoke biases which influence subsequent memory processing. The production of this bias may be an adaptive mechanism. Making the decision about retrieval or creation of memory uses up resources, and it is very rarely that our experiences rapidly switch between the familiar and the novel. It could thus be advantageous for our nervous system to be more receptive to change in new environments and less sensitive to irregularities in familiar environments.
You can read more about this research here.

Published by

Shweta Ramdas

Beginning life as a grad student studying human genetics.