Marie Banich has spent her career trying to understand how the brain works with information. She has also noticed that some of her anxious relatives have a way of getting stuck on a thought and not being able to move on from it. “People have these thoughts they can’t get rid of,” Banich told me. “I wanted to know if there are mechanisms for getting rid of those thoughts that are going around and around on virtual repeat.”
Now a new study by Banich of University of Colorado Boulder, Jarrod Lewis-Peacock of the University of Texas Austin and their team takes an innovative approach to the problem. By combining brain imaging with machine learning, the team was able to look inside the mind and study what happens when we try to stop thinking about something. It turns out that to truly make room for new information, we have to suppress the old.
The issue is working memory. Working memory is what we use to store pieces of information we are currently working with. In order to work on a problem, we need to hold information in our working memory. But working memory is limited: we only have room for 3 to 4 pieces of information at a time. That means we also need to be able to dump information that is irrelevant or distracting from the issue at hand. Up until now, researchers have found it challenging to study the actual mechanisms we use to do this.
Banich, who is a professor of psychology and neuroscience, wanted to understand how we make room in our working memory. She and her colleagues combined functional MRI imaging of the brain and machine learning to track when people truly stop thinking about something.
The team began by showing study participants images and asking them to retain them. Then they were able to track a specific signature or trace of each image in the brain. Later, they were able to tell when someone had completely stopped thinking about that image because that trace went away on the MRI. “For the first time we have a way of verifying whether someone has stopped thinking about something,” she said.
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Ways to clear the mind
What her team showed was that there are three distinct ways to flush information out of our working memory. Each method works, but with couple of a key differences. The methods are replace, clear, and suppress.
“Replace works the most quickly,” said Banich. “When we asked someone to replace one image with a different image, they were able to do it fast.” When someone was told to clear their mind, the image also faded fairly quickly although not as fast as with replace.
The third method worked differently. “It’s counterintuitive,” says Banich, “when you ask someone to suppress an image, it takes longer to get rid of that information. I think it’s because they have to focus on that information in order to suppress it.” Given that suppressing an image takes the longest, it might not seem valuable. But in fact, suppress was actually unique among the methods when it came to what happens next.
“The question then becomes whether the information has been removed effectively enough so as to not interfere with NEW information that needs to be put into working memory,” Banich told me. “We found that if you really want a new idea to come into your mind, you need to deliberately force yourself to stop thinking about the old one.” Suppression allowed that new information to come into memory with no interference.
Similar information causes interference
Because the fMRI imaging allowed the researchers to trace a pattern for each piece of information, they were able to see the fidelity of encoding, or how faithfully the brain saved that information. The brain did a good job if two different pieces of information were not related, such as an image of an apple and an image of Barack Obama. In this case, each image was encoded with fidelity.
But when the study participants were asked to replace an image of Bill Clinton right after Barack Obama, they did not record the image of Bill Clinton with the same accuracy. Replacing and clearing did lead the trace of the original image in the brain to fade, but at least some pieces of information about the original item remained. And that old information interfered with the fidelity of encoding the new information.
“If you’ve just put something in, if you try to put in something similar there is interference,” Banich explained. “Obama and Clinton are both past presidents, and they share similar information. Because there are too many overlapping features the brain has a hard time distinguishing them.” And that may have some interesting implications for learning theory.
However, when the participants were told to suppress the image of Barack Obama, and then think of Bill Clinton the new image was recorded without interference. Replace and clear move information out of our working memory’s focus, but only suppress really “dumps” the item from working memory in its entirety. Only suppressing the old information makes room for the new to come in without interference.
“This distinction is kind of subtle but important,” Banich emphasizes. “It’s almost as if all three methods allow you to “look away” from information you just had in working memory (which is why the original pattern fades), but only suppress really “erases” the information.
Exploring working memory
It’s worth taking a moment to consider what this research tells us and what it does not. Banich was quick to warn that we can’t generalize this study to issues like how we manage our emotions. “We are not talking about suppressing your feelings,” she said. This study was purely looking at our working memory, the section of our brain processes information so we can solve problems. And she also emphasized that each method of decluttering our working memory has its time and place.
This study lays the groundwork for looking at how working memory works in a variety of situations. Because the researchers have pioneered a way to actually see what is going on in the mind, they can now look at how it all works in more complex situations. This study looks at relatively neutral information, but what happens when the images are emotionally charged?
The research team just applied to the NIH, hoping to study valenced images of either positive or negative information. They also want to know if people’s level of anxiety or depression impacts which of the three methods to remove information from working memory is best. Or if giving people realtime feedback changes things.
In the end, the study suggests that we are actually able to control what we focus on, and gives us three tools to use while studying or trying to generate innovative ideas.