There has long been convincing evidence that recalling a memory can cause changes in that memory, potentially weakening it, strengthening it, or otherwise altering it. A new study, published in Nature Neuroscience by researchers from the University of Birmingham, the MRC Cognition and Brain Sciences Unit, and the Behavioral and Clinical Neurosciences Institute, presents a convincing argument that the weakening of old memories may be an adaptive function, one that helps the brain integrate new memories with existing ones.
The researchers were able to watch subjects’ brain activity as memories were recalled using a functional Magnetic Resonance Imaging (fMRI) machine. An fMRI machine allows scientists to see changes in brain activity by producing images that show where oxygen-rich blood is flowing within the brain.
Subjects were shown 144 pairs of pictures/words while in the fMRI machine, and their brain activity was observed. Then, the subjects entered a learning phase, in which they were trained on 72 picture-word pairs, a subset of the initial 144. They were asked to construct a highly detailed association between the pictures and the words, using intricate mental imagery. They were then asked to learn a second set of associations for each word; these served as competition for the first set.