The research, presented today at the Annual Meeting of the Society for Neuroscience, helps to resolve questions about how working memory – a function that allows people to perform tasks as diverse as making toast to solving complex math problems – develops and changes from childhood to adulthood.
"This study gives us a good picture of how our ability to have voluntary control over our behavior using working memory changes and improves with maturity," said Beatriz Luna, Ph.D., associate professor of psychiatry at the University of Pittsburgh School of Medicine.
"Anyone with kids or teenagers knows that they can make irrational decisions when they are under stress," said Dr. Luna. "That is not just because they are trying to be difficult – kids simply are not yet able to access the brain regions that allow adults to react in a more controlled way. What this may mean is that adolescents may be able to act like adults under normal conditions, but under stress they may go back to a more instinctual, less thought-out response."
Working memory is where the brain stores information used to make immediate calculations, similar to the random access memory (RAM) in a computer. Like RAM, the information stored in working memory is dumped when it is no longer needed. Working memory allows the brain to take in information and create planned responses using abstract thought. Without it, human behavior would consist mostly of reflexive actions, and humans would not have been able to develop higher mental abilities.
In a group of 20 healthy 8- to 30-year-olds, Dr. Luna and her colleagues used a test called an oculomotor delayed response task to track memory-guided saccades (eye movements) while imaging their brains using functional magnetic resonance imaging (fMRI). Study participants briefly were shown a pinpoint of light and asked to remember where the light appeared. Ten seconds later, they were asked to look at the location where the light had been using just their memory. The 10-second time lapse was chosen because it would force the subjects to use their working memory – and not short- or long-term memory.
Results of the imaging study showed that pre-adolescent children relied most heavily on the prefrontal and parietal regions of the brain during the task; adolescents used those regions plus the anterior cingulate; and in adults, a third area of the brain, the medial temporal lobe, was brought in to support the functions of the other areas.
Adults did best with the saccade test probably because the medial temporal lobe helps refine encoding of information into working memory. In practical situations, introduction of the medial temporal lobe into the working memory process likely provides the kick needed to keep information around long enough and clearly enough for the brain to mull it over and make a rational, informed decision rather than an impulsive, reflexive action.
"Understanding working memory will inform us about how thinking occurs and how it is linked to other brain processes – and because working memory also is one of the major brain systems impaired in many psychiatric illnesses, understanding these links could inform the development of new treatments," said Dr. Luna.