The research, published today in Nature Neuroscience, is the first to isolate the adaptive forgetting mechanism in the human brain. The brain imaging study shows that the mechanism itself is implemented by the suppression of unique patterns in the cortex that underlie competing memories. Via this mechanism, remembering dynamically alters which aspects of our past remain accessible.



In a study funded by the Medical Research Council (MRC), researchers monitored patterns of brain activity in the participants using magnetic resonance imaging (MRI) scans while the participants were asked to recall individual memories based on images they had been shown earlier.



The team from the University of Cambridge, the MRC Cognition and Brain Sciences Unit, Cambridge, and the University of Birmingham, was able to track the brain activity induced by individual memories and show how this suppressed others by dividing the brain into tiny voxels (3D pixels). Based on the fine-grained activation patterns of these voxels, the researchers were able to witness the neural fate of individual memories as they were initially reactivated, and subsequently suppressed.



Over the course of four selective retrievals the participants in the study were cued to retrieve a target memory, which became more vivid with each trial. Competing memories were less well reactivated as each trial was carried out, and indeed were pushed below baseline expectations for memory, supporting the idea that an active suppression of memory was taking place.



Dr Michael Anderson from the MRC Cognition and Brain Sciences Unit and the Behavioural and Clinical Neurosciences Institute at the University of Cambridge said: “People are used to thinking of forgetting as something passive. Our research reveals that people are more engaged than they realise in shaping what they remember of their lives. The idea that the very act of remembering can cause forgetting is surprising, and could tell us more about selective memory and even self-deception.”



Dr Maria Wimber from the University of Birmingham added: “Forgetting is often viewed as a negative thing, but of course, it can be incredibly useful when trying to overcome a negative memory from our past. So there are opportunities for this to be applied in areas to really help people.”



The team note that their findings may have implications for the judicial process, for example, in eyewitness testimonies. When a witness is asked to recall specific information about an event and is quizzed time and time again, it could well be to the detriment of associated memories, giving the impression that their memory is sketchy.



Studying the neural basis of forgetting has proven challenging in the past because the ’engram’ – the unique neural fingerprint that an experience leaves in our memory – has been difficult to pinpoint in brain activity. By capitalising on the relationship between perception and memory, the study detected neural activity caused by the activation of individual memories, giving a unique window into the invisible neurocognitive processes triggered when a reminder recapitulates several competing memories.



Adapted from a press release by the Medical Research Council.



Reference

Wimber, M et al. Retrieval induces adaptive forgetting of competing memories via cortical pattern suppression. Nature Neuroscience; 16 March 2015