Based on their results, Stanford University (California) psychology researchers Brie Kuhl and Anthony Wagner state, “Remembering something actually has a cost for memories that are related but irrelevant. But this cost is beneficial: The brain's ability to weaken unimportant memories and experiences enables it to function more efficiently in the future.”

The two researchers used functional magnetic resonance imaging (fMRI) on the prefrontal cortex region of the brain of subjects. The technique of fMRI makes use of the MRI to measure the naemodynamic response (dynamic regulation of blood in the brain) associated to neural activity in the brain of humans and other animals.

The prefrontal cortex is located behind of the forehead. This region of the brain selectively controls what memories it considers important and what it considers not so important. This filtering of information helps the next time the important memory is recalled by the brain. It is easier for the brain to recall the important bit of information because other less important memories are weakened in the brain’s ability to recall them.

For their study, Kuhl and Wagner flashed cards to twenty Stanford University students, between the ages of 18 and 32 years. Forty words were used on the flash cards, such as “Attic”. Associated with each word were six attached associate words, such as “-junk” and “-dust”. In all, a set of six word pairs (one word and six associate words)—such as “Attic-dust”, “Attic-junk”, “Attic-clothes”, “Attic-space”, “Attic-storage”, and “Attic-stairs”—were flashed for four seconds on a screen.

The technique used by the researchers was developed in order to build six memories, one for each word pair. After the subjects tried to memorize the six word pairs, the researchers gave the subjects a hint as to the identity of one of the word-pairs, say “Attic-d”—for “Attic-dust”.

The subjects practiced remembering the six word pairs three times with the hint. The first time, a scanner recorded their brain activity as the brain tried to remember the word pair related to “Attic-d”. Each subsequent time the subjects practiced remembering the word pair, their frontal lobes of the brain became less active.

After about twenty minutes, the subjects were tested on all the word pairs. They remembered better the word pairs in which the hint was given (the more important information) and remembered less the word pairs in which the hint was not given (the less important inforation).

Although forgetting is a frustrating part of daily life, according to the researchers, it actually has a benefit—to allow the brain to more easily remember the more important information with less brain-power so the brain can do other necessary and relevant tasks.

This study reveals for the first time the neural benefits of forgetting. The neural network of the brain does not need to work as hard in successive tries at remembering because it can eventually filter the more important information from the less important information.

Kuhl and Wagner’s findings, along with their collaborators Nicole Dudukovic and Itamar Kahn, are published online in the June 3, 2007 issue of Nature Neuroscience in an article titled “Decreased Demands on Cognitive Control Reveal the Neural Processing Benefits of Forgetting”.

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