Forget About It: Investigating How We Purge Thoughts From Our Mind
Forgetting isn’t always easy, but cognitive neuroscientists are working to understand exactly how we do it and what it means for patients with neurocognitive disorders. While much research has focused on how the brain retains information, there is growing interest in the mechanisms behind removing irrelevant or unwanted information from our working memory. From getting rid of that annoying earworm to stopping intrusive thoughts, the study of forgetting is shedding light on how we can improve focus and attention.
Marie Banich, chairing a session about new research on forgetting at the Cognitive Neuroscience Society (CNS) annual meeting in San Francisco, highlights the surprising fact that “people can control what and how they forget.” Banich explains that control over working memory is essential for switching between and re-prioritizing tasks, so it is not entirely unexpected that we can remove information from “the focus of our thoughts.”
Researchers, including Banich and Festini, have discovered specific mechanisms that people use to remove information from their working memory. They have also found that forgetting is not automatic and requires significant effort.
Festini adds, “We’ve found that intentionally forgetting no-longer-relevant information from the mind is beneficial, but it doesn’t happen automatically.”
The researchers aim to not only improve our understanding of attention and focus but also identify potential clinical targets to aid patients with neurocognitive disorders such as depression, schizophrenia, PTSD, and ADHD.
Tracking forgetting
Banich developed an interest in studying forgetting after experiencing the loss of someone to suicide. This led her to contemplate the dangers of intrusive thoughts for individuals with depression and related disorders. Banich explains that the content that gets stuck in the mind can vary depending on the disorder. For instance, people with schizophrenia might be consumed with paranoid thoughts, while those with obsessive-compulsive disorder may be worried about germs, and those with anxiety may get stuck thinking about negative events that might happen in the future. However, despite the differences in the content, the process remains the same, with the thoughts becoming the focus of attention and difficult to remove.
“It’s the same process. The thoughts are going round and round, becoming the focus of attention and difficult to remove.”
The difficulty in treating neurocognitive disorders stems from patients relying on self-reporting their symptoms, making it challenging to determine whether they are truly improving or still negatively ruminating. To address this challenge, cognitive neuroscientist Marie Banich and her team have been working to track the process of purging a thought from the mind. Their research has identified three distinct neurological mechanisms by which people remove information from working memory: replacing the thought with something else, suppressing the thought, or clearing the mind entirely. This framework, which relies on fMRI imaging, machine learning, and other technological advancements, has taken years to develop and has the potential to revolutionize how neurocognitive disorders are diagnosed and treated.
During their research, Banich and her team instructed participants to think about different categories of information (such as faces, places, and fruit) while in the fMRI scanner. They trained a computer on the resulting neural patterns for each category and then asked participants to intentionally forget information in these categories, monitoring whether the brain pattern remained present. By doing so, they were able to identify the neural pattern of brain activation associated with each of the three mechanisms of forgetting: replacing the thought with something else, suppressing the memory, or clearing all thoughts.
Their findings have led them to identify four distinct brain networks that activate when a memory is maintained or purged through one of the three mechanisms: the somatomotor network, the visual network, the default mode network, and the frontoparietal control network. According to their research, the frontoparietal control network likely plays a significant and unique role in suppressing a thought or clearing thoughts entirely.
By identifying specific brain networks, the research provides an opportunity to investigate individual differences in forgetting. Banich suggests that this could lead to developing metrics for people who struggle with controlling their thoughts. She raises the possibility that the frontoparietal network in individuals who have difficulty controlling their thoughts might not be able to distinguish between the different forgetting mechanisms or that the mechanisms may be jumbled together. Future research will explore whether biofeedback can help participants control the process of removing unwanted information while they are in the fMRI scanner.
Effortful Forgetting: The Science of Purging Unwanted Thoughts
Proactive interference, or the struggle to learn something new that overlaps with existing knowledge, can complicate the process of forgetting. For instance, it can be challenging to learn Emma Stone’s face when you already know Emma Watson’s. According to Marie Banich’s research, to overcome this, suppressing a thought is more efficient than replacing it.
Researchers, including Sara Festini and her team, presented their work in San Francisco and found that voluntarily forgetting a piece of information can reduce proactive interference. This has a positive effect on an individual’s ability to learn new information more easily.
“Proactive interference occurs, for example, when you accidentally walk to where you parked your car yesterday instead of where you parked your car today,” Festini adds. “We’ve shown that by voluntarily removing information from working memory, it makes the information less susceptible to detrimental forms of memory interference, like false memories and proactive interference.”
According to Festini’s studies, participants were instructed to forget a piece of information through explicit instructions that included a “forget cue,” following an established paradigm. She notes that these cues are not solely a creation of the lab and that in daily life, implicit forget cues may occur when people change their orders in drive-thru restaurants or when instructors ask their students to disregard an earlier statement if it is no longer relevant or inaccurate.
According to Festini’s research, forget cues are effective in facilitating the goal-directed removal of information from working memory, and this process is distinct and more beneficial than just stopping the processing of information. However, other attention-demanding tasks can impede the efficiency of directed forgetting within working memory, indicating that forgetting is a deliberate and effortful process, consistent with Banich’s findings.
Festini and her colleagues have conducted studies on directed forgetting in both younger and older adults. The results of these studies suggest that explicit forget cues can help mitigate interference in working memory in both age groups, but directed forgetting in older adults is generally impaired compared to younger adults. While their research has not specifically examined clinical applications, it suggests that individuals with major depressive disorder or ADHD may find it more difficult to voluntarily remove information from their working memory.
Banich has suggested that this body of work may contribute to understanding and treating PTSD. People with PTSD have a tendency to overgeneralize memories, where a specific trigger can cause a cascade of memories. Since forgetting requires effort and is more effective when specifically targeted, individuals with PTSD may find it challenging to identify and suppress the specific memory.
“There is a paradoxical effect that if you’re told to stop thinking about something, you actually have to identify and think about it to suppress it,” she adds.
At present, Festini is conducting a new investigation on how and when individuals remove information from their working memory that is considered less significant or valuable, without the provision of explicit “forget” instructions.
“I’m curious to understand what the tipping point is to motivate someone to engage in effortful removal of information from working memory,” she adds, “since there are clear benefits to the removal of less valuable information, but this removal process is attentionally demanding.”
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