Normally, it takes years or decades after a brand new discovery about the brain for any practical implications to emerge. But this study by MIT neuroscientists could be put to immediate use in designing more effective cognitive therapy, smarter brain games, better “heads up displays,” and much more. The study will appear on the website of the Proceedings of the National Academy of Sciences on Monday, June 20, 2011.
Researchers have known for over a hundred years that we can only hold about four things in our minds at once. This capacity limitation of our working memory (our mental sketchpad) varies somewhat among individuals, and the more you can hold in mind at once, the more complex your thoughts and the higher your IQ tends to be. But although this limitation is a fundamental feature of cognition and intelligence, researchers knew nothing about its neural basis.
Monkeys, amazingly, have the same working memory capacity as humans, so Earl Miller, the Picower Professor of Neuroscience in MIT’s Picower Institute for Learning and Memory, and Timothy Buschman, a post doctoral researcher in his lab, investigated the neural basis of this capacity limitation in two monkeys performing the same test used to explore working memory in humans. First the researchers displayed an array of two to five colored squares, then a blank screen, and then the same array in which one of the squares changed colored. The task was to detect this change and look at the changed square.
As the monkeys performed this task, Buschman recorded simultaneously from neurons in two brain areas related to encoding visual perceptions (the parietal cortex) and holding them in mind (the prefrontal cortex). As expected, the more squares in the array, the worse the performance.
“But surprisingly, we found that monkeys, and by extension humans, do not have a general capacity in the brain,” says Miller. “Rather, they have two independent, smaller capacities in the right and left halves of the visual space. It was as if two separate brains — the two cerebral hemispheres — were looking at different halves of visual space.”
In other words, monkeys, and by extension humans, do not have a capacity of four objects, but of two plus two. If the object to remember appears on the right side of the visual space, it does not matter how many objects are on the left side. The left may contain five objects, but as long as the right side contains only two, monkeys easily remember it. Conversely, if the right side contains three objects and the left side only one, their capacity for remembering the key object on the right is exceeded and so they may forget it.
This study resolves two long-standing debates in the field. Does our working memory function like slots, and after our four slots are filled with objects we cannot take in any more; or does it function like a pool that can accept more than four objects, but as the pool fills the information about each object gets thinner? And is the capacity limit a failure of perception, or of memory?
“Our study shows that both the slot and pool models are true,” says Miller. “The two hemispheres of the visual brain work like slots, but within each slot, it’s a pool. We also found that the bottleneck is not in the remembering, it is in the perceiving.” That is, when the capacity for each slot is exceeded, the information does not get encoded very well. The neural recordings showed information about the objects being lost even as the monkeys were viewing them, not later as they were remembering what they had seen.
This effect in visual working memory may not hold for other forms of memory, but visual perception is one of the primary ways that humans process the world, so its impact is both far reaching in terms of understanding the brain and human consciousness and in practical terms.
“The fact that we have different capacities in each hemisphere implies that we should present information in a way that does not overtax one hemisphere while under-taxing the other,” explains Buschman. “For example, heads-up displays (transparent projections of information that a driver or pilot would normally need to look down at the dashboard to see) show a lot of data. Our results suggest that you want to put that information evenly on both sides of the visual field to maximize the amount of information that gets into the brain.”
Likewise, cognitive therapies for improving working memory (and in brain games designed to keep it young and nimble) should present information in a way that trains each hemisphere separately. Biomedical monitors that currently have one column of information should balance it in right and left columns, and security personnel could take in more information if displays scrolled vertically rather than horizontally, which wastes the independent capacities on the right and left. The researchers are forming collaborations to develop many of these ideas.
Their next basic research project is to discover why this perceptual bottleneck occurs in the first place, Miller says. “That would give us a deep understanding of how the brain represents information and would give us the first real insights into consciousness.”
This research was funded by the National Institutes of Health and the National Institute of Mental Health.
Marta Buczek | EurekAlert!
Multi-institutional collaboration uncovers how molecular machines assemble
02.12.2016 | Salk Institute
Fertilized egg cells trigger and monitor loss of sperm’s epigenetic memory
02.12.2016 | IMBA - Institut für Molekulare Biotechnologie der Österreichischen Akademie der Wissenschaften GmbH
A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.
Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...
In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.
“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...
The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.
The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...
Broadband rotational spectroscopy unravels structural reshaping of isolated molecules in the gas phase to accommodate water
In two recent publications in the Journal of Chemical Physics and in the Journal of Physical Chemistry Letters, researchers around Melanie Schnell from the Max...
The efficiency of power electronic systems is not solely dependent on electrical efficiency but also on weight, for example, in mobile systems. When the weight of relevant components and devices in airplanes, for instance, is reduced, fuel savings can be achieved and correspondingly greenhouse gas emissions decreased. New materials and components based on gallium nitride (GaN) can help to reduce weight and increase the efficiency. With these new materials, power electronic switches can be operated at higher switching frequency, resulting in higher power density and lower material costs.
Researchers at the Fraunhofer Institute for Solar Energy Systems ISE together with partners have investigated how these materials can be used to make power...
16.11.2016 | Event News
01.11.2016 | Event News
14.10.2016 | Event News
02.12.2016 | Medical Engineering
02.12.2016 | Agricultural and Forestry Science
02.12.2016 | Physics and Astronomy