The Brain’s Working-Memory Capacity Revealed

A new study provides a deeper look into why most people’s brains have a limited capacity to memorize information. The knowledge gained in the paper, which was published in last week’s issue of the Proceedings of the National Academy of Science, could help hone cognition-boosting games and visual displays for airplane pilots and automobile drivers.

One of the more basic limitations of our intelligence is the maximum number of information pieces the brain can memorize and retrieve on a short-term basis. This is known as the maximum capacity of the working memory.

                                                    

A team from the Massachusetts Institute of Technology (MIT) in Cambridge, Mass., tested the working-memory capacity of two macaque monkeys. The researchers were not surprised to find that four is the maximum number of objects the macaques could remember information about at any given time. That’s the same maximum capacity of most people’s working memory, according to earlier studies.

(Monkey's Can Recall Simple Shapes)

But the MIT team members did not expect their major finding, which was that the left and right visual fields—and hence the right and left hemispheres of the brain where information from each field, respectively, is processed—seem to be independent. Neural recordings uncovered the fact that the monkeys were limited to recalling two objects in their right and left visual fields.

“Before the study, we expected that information resources in your brain could be used in a very flexible way —that one hemisphere can lend a hand when the other hemisphere is only using part of its capacity,” explained lead researcher Timothy Buschman, PhD. “But it seems that’s not the case. There are limitations—although we don’t yet know whether these are physical or something else—to how information from the outside world can be represented internally in the brain and hence remembered, accessed and utilized.”

Dr. Buschman is a postdoctoral associate at the Picower Institute for Learning and Memory in the Department of Brain and Cognitive Sciences at MIT. He, along with his supervisor and institute associate director Earl Miller, Ph.D, and two other researchers simultaneously recorded the firing of neurons in the prefrontal and parietal cortices of the brains of the two macaques. The monkeys watched a computer screen that displayed very briefly, either two, three, four, or five coloured squares. A short time later the monkeys were shown the same display but with one square coloured differently. The macaques received a reward for glancing toward the single changed square.

Each monkey could only remember information regarding an average of four coloured squares. In addition, the neural recordings showed that the monkeys could only recall two objects on each side of their field of vision. The limitation occurred during memory encoding, not during memory retrieval.

“Why our working memory has a limited capacity has been the subject of an ongoing debate among researchers,” said Dr. Buschman. “One group believes it’s because there only a limited number of objects we can hold in our mind at one time. Other people think we have a pool of available resources that we can divvy up—and capacity limitations happen as we divide up those resources for use with particular memories, overextending ourselves too much. And our study shows a hybrid model is likely what is happening— resources are pooled, except there are actually two pools. And we can’t take resources from one pool and use them to help out the other pool.”

Dr. Buschman noted the separate pools of working-memory resources can be harnessed in several practical ways. He and Dr. Miller hope to build visual displays, such as heads-up displays (transparent displays of information that present information without requiring the viewer to look away, initially developed for aviation) that have similar amounts of information in the left and right sides. This would not overload viewers’ working-memory capacity and hence would allow more information on the displays to be retained and accessed.

“In addition, better brain-training games can be developed that isolate each visual hemisphere, targeting training to weaknesses in each hemisphere alone,” concluded Dr. Buschman.

Via:  Rosemary Frei, Freelance Journalist for “Betterbrainbetterlife.com”