Watching the brain forget

Researchers from the School of Psychology, together with the MRC Cognition and Brain Sciences Unit in Cambridge, have been able to track how individual memories are forgotten in the human brain.

In their study, published in Nature Neuroscience this week, Dr Maria Wimber and her colleagues demonstrate that forgetting is not a passive process at all – rather, the brain helps us to actively get rid of irrelevant or distracting memories. This process takes place every time we actively use our memory: while remembering a particular memory, our brain applies cognitive control to inhibit competing memory traces that would otherwise interfere with our memory search. Over time, this adaptive process ensures optimal access to the memories that we frequently need.

So far, it has been difficult to directly observe forgetting in the human brain, because the “engram”, that is, the unique trace that an experience leaves in memory, has been hard to pinpoint. The researchers developed a novel method of analysing brain imaging data called “canonical pattern tracking”.

This method divides the brain into tiny voxels (i.e., 3D pixels). Based on the fine-grained patterns of brain activity in these voxels, the researchers were able to tell which memories were active at any given time in their subjects’ brains, and importantly, which memories were being inhibited. Moreover, they could demonstrate that those unique memories that were being inhibited were more likely to be forgotten on a later recognition test, and that prefrontal brain regions control which memories are being inhibited. 

Many of us think of forgetting as a failure of the brain, like a bug in our memory software that most of us would like to fix. This research strongly suggests that forgetting plays a much more adaptive role in shaping our long-term memory.

The paper is the result of a collaboration between Maria Wimber and Cambridge based researchers Michael C. Anderson, Arjen Alink, Ian Charest, and Nikolaus Kriegeskorte.

The project was funded by the German Research Foundation (DFG).

View the full paper on nature.com

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