When recalling individual memories, the brain actively causes the forgetting of similar but irrelevant memories, reports a brain imaging study published this week in Nature Neuroscience.
Remembering a particular place or event causes forgetting of other experiences that might interfere with the retrieval of that memory. Maria Wimber and colleagues demonstrated how the brain carries out this adaptive forgetting process by showing participants words paired with a picture of either a face or an object. The same word was presented with a different face or object at different times (such as the word “sand” alongside a picture of Marilyn Monroe or a hat). When asked to remember which picture was shown first with a particular word, participants were more likely to forget the other picture.
Using brain imaging, the authors detected what participants were remembering based on patterns of activity in visual areas of the brain. They observed that the pattern of activity corresponding to the secondary picture was decreased after remembering the first, and that the greater this decrease in activity, the more likely the second picture was forgotten entirely. Activity in the prefrontal cortex, a brain region involved in inhibiting interfering memories, predicted both the amount of pattern decrease as well as the degree of forgetting.