Summary How do you suppress a thought or memory? This question has been puzzling since it is difficult to know how to detect the disappearance of a memory trace. However, research in cognitive and cognitive neuroscience is now shedding light on this topic. From that perspective, the goal of this symposium is to explore recent theoretical ideas and empirical findings that provide insights into how information is deleted or inhibited in memory. Evidence from behavioral approaches, functional neuroimaging and EEG will be used to address this important issue. Different methods are considered by which information can be removed, such as replacement versus deletion . These recent studies suggest an important contrast between the mechanisms invoked for the removal of information from working memory, which requires a diversion of attention from a thought and/or the probable inactivation of a representation, compared to long-term memory. , which can be achieved by closing access to or processing of the hippocampus and/or modality-relevant regions of the posterior cortex. Finally, the implications of these findings for psychopathological states, such as recurrent and intrusive (negative) thoughts, are considered. |
Removal of information from working memory through three different mechanisms
Marie Banich, University of Colorado Boulder
How can we, as scientists, determine when someone has stopped thinking about something? Put another way, how can we find an experimental signature of a thought that no longer exists? Our behavioral and neuroimaging research addresses this question to elucidate the cognitive control mechanisms that allow information in working memory to be actively deleted. Our approach, using a combination of functional neuroimaging and machine learning techniques (including multi-voxel pattern analysis), along with behavioral experiments, has been able to track a thought and then verify that it was indeed deleted. Furthermore, this research provides evidence for at least three different ways to remove information from working memory: replacing it with something else, specifically targeting it for suppression, and clearing the mind of all thoughts. In this talk, I will discuss a) the neural mechanisms that enable each of these three types of operations, b) provide evidence on the time course of each deletion operation, and c) elucidate the consequences of these deletion operations for the encoding of new information, which is critical for new learning. The implications of this work are several for psychological and psychiatric disorders, many of which are characterized by recurrent or intrusive thoughts that individuals cannot eliminate from the current focus of attention.
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Forgetting is not always easy. If you’ve ever tried to erase that annoying intrusive thought from your mind or stopped thinking about whether you locked the door after leaving the house, you know how disturbing it can be to think about something irrelevant to the task at hand. While much of the work in cognitive neuroscience focuses on how the human brain remembers and retains information, some cognitive neuroscientists have focused on forgetting , working to track exactly how we forget information and what it means for patients suffering from neurocognitive disorders. .
“It may sound surprising that people can control what and how they forget,” says Marie Banich of the University of Colorado, Boulder, who will chair a session on new research on forgetting at the annual meeting of the Cognitive Neuroscience Society (CNS). for its acronym in English) in San Francisco. “But control over working memory is essential for changing and reprioritizing tasks. “So, in many ways, it is not surprising that we have control over the ability to remove information from the focus of our thoughts.”
In new work presented by Banich and others, researchers identified different mechanisms by which people delete information from their working memory and also discovered that forgetting requires a lot of effort . “We found that intentionally forgetting information that is no longer relevant from the mind is beneficial , but it doesn’t happen automatically,” says Sara Festini of the University of Tampa, who will also present new work at the CNS conference. The hope is that the body of work can lead not only to a better understanding of attention and focus, but also to clinical goals to help patients suffering from disorders ranging from depression and schizophrenia to PTSD and ADHD. .
Tracking the loss of a thought
Banich became interested in understanding forgetting after losing someone to suicide. Her experience made her think about the dangers of intrusive thoughts for people suffering from depression and related disorders.
“The content that gets stuck in the mind varies with different disorders,” explains Banich. For example, people with schizophrenia may be consumed by paranoid thoughts, while those with obsessive-compulsive disorder may be worried about germs, and someone with anxiety may get stuck thinking about bad things that could happen in the future. “But it’s the same process,” she says. “Thoughts go around and around, becoming the focus of attention and difficult to eliminate.”
Complicating the treatment of these disorders is the fact that many rely on self-report of symptoms, and even if a patient reports improvement, they may still be ruminating negatively. That challenge led Banich, a trained cognitive neuroscientist, down a path to answer the question: How can we tell if someone has truly stopped thinking about something?
Step by step, Banich and his colleagues have been learning how to track what happens when someone tries to remove a thought from their mind. Their latest work builds on earlier peer-reviewed work that documented three neurologically distinct ways people remove information from their working memory:
- Replacing the thought with something else
- Suppressing that thought
- Clearing your mind of all thoughts.
This seemingly simple framework has required many years of work, aided by functional magnetic resonance imaging, machine learning, and other technological and experimental advances. It started, Banich said, with realizing in the middle of a night that “we can actually use neuroimaging to verify that someone stopped thinking about something.”
By asking participants to think about information in different categories (e.g., faces, places, fruits) while in the fMRI scanner, Banich and his team first trained a computer on the resulting neural patterns for the categories and examples of each. one. They then asked study participants to forget information in different categories, checking to see if it was deleted by tracking whether the brain pattern was still present. They also identified the neural pattern of brain activation associated with each of the three forgetting mechanisms, whether they replaced the thought of a face like Emma Watson with an object, like the Golden Gate Bridge, suppressed Emma Watson’s memory, or erased all the thoughts
Through this work, they have identified four brain networks that are clearly activated if memory is maintained or purged through one of three mechanisms:
- The somatomotor network
- The visual network
- Default mode network
- The frontoparietal control network
Their work suggests that when the brain suppresses a thought or deletes it entirely, the frontoparietal control network likely plays a prominent and distinct role.
By identifying these specific brain networks, the research offers a way forward to investigate potential differences between individuals. viduals on how they forget. “Can we get some metrics for people who might have difficulty controlling their thoughts?” Banich asks. “Maybe the frontoparietal network in people who have difficulty controlling their thoughts can’t differentiate between those mechanisms, or are they all confused?” In future work, Banich and her colleagues will also look at whether they can use biofeedback while participants are in the fMRI scanner to see if that can help people control the mechanism for removing unwanted information.
Making an effort to forget
An important part of this work has been analyzing "proactive interference" , which can occur when the brain is trying to learn something new that overlaps in category with something it already has in mind, such as trying to learn Emma Stone’s face in instead of Emma Watson’s.
The conclusion of Banich’s work has been that, partly due to proactive interference , suppressing a thought is more efficient than replacing it.
In fact, in work by Sara Festini and her colleagues presented in San Francisco, researchers found that one of the benefits of voluntarily forgetting information is that it reduces proactive interference, making it easier for someone to learn something new. “Proactive interference occurs, for example, when she accidentally walks to where she parked her car yesterday instead of where she parked her car today,” Festini says. "We have shown that by voluntarily removing information from working memory, the information becomes less susceptible to harmful forms of memory interference, such as false memories and proactive interference."
In Festini’s studies, researchers, following an established paradigm, direct their participants to forget through explicit instructions that include a "forgetting cue." These signals, she says, are not just a lab invention. In real life, a forgetting signal might appear implicitly when collecting self-service orders: If someone changes their order, they might say "Oh, never mind! I don’t want that anymore." Or in class, an instructor might tell her students to ignore a previous statement if it was inaccurate or no longer relevant.
Evidence from Festini’s lab suggests not only that these forgetting signals work, but that they promote the removal of information from goal-directed working memory in a process that is "different from and more beneficial than simply reducing information processing." ", she says. "We also have evidence that other tasks that require attention can alter the efficiency of directed forgetting within working memory." That makes the process of forgetting laborious and different from simply discontinuing information processing, echoing Banich’s work.
In other studies, Festini and colleagues found that directed forgetting in older adults is impaired compared to younger adults, but that explicit forgetting cues can still help mitigate interference in working memory for both younger adults. as adults. Although Festini’s team’s research has not specifically examined clinical applications, it suggests that voluntarily removing information from working memory may be more difficult for people with major depressive disorder or ADHD, for example.
Banich has also speculated about how the body of work might help contribute to the understanding and treatment of PTSD, noting that people with PTSD tend to overgeneralize memories (for example, when a flying vehicle can trigger a memory of an explosion). Because the forgetting process appears to require effort and is best when it is targeted, people with PTSD may have difficulty identifying and then suppressing the specific memory. “There’s a paradoxical effect that if you’re told to stop thinking about something, you actually have to identify it and think about it to repress it,” she says.
Festini is currently conducting a new study on how and when people delete information from working memory that is designated as less valuable or less important, without providing specific "forgetting" instructions. "I’m curious to understand what the tipping point is for motivating someone to engage in effortful removal of information from working memory," he says, "since there are clear benefits to removing less valuable information, but this process of elimination is attentional demanding.
