New research published in Nature Communications provides unique insights into the process of consciously purging information from the brain’s working memory system. The study suggests that there are distinct mechanisms by which people can remove thoughts from their mind, which have varying levels of effectiveness.
“I have been studying how the brain discards information for a number of years. I am fascinated by the powerful mental processes, which we so often take for granted, that allow us to juggle myriad thoughts and accomplish goals in our daily lives,” said study author Jarrod Lewis-Peacock, an associate professor at The University of Texas at Austin and head of the Lew Pea Lab.
“The control, or lack thereof, of thoughts plays a critical role in many mental health disorders as well. Along with my wonderful collaborator Dr. Marie Banich at the University of Colorado Boulder, who has special expertise in cognitive control and psychopathology, we decided to bring a cutting-edge neuroscientific approach to the age-old question of ‘How do we stop thinking a thought?’
In the study, the researchers used functional magnetic resonance imaging to record the brain activity of 60 volunteers as they viewed images and tried to remove thoughts from their working memory. The participants were shown pictures of faces, fruits and scenes and asked to maintain the thought of them for four seconds. By using machine learning approaches, the researchers were able to identify individualized brain signatures showing precisely what each person’s brain looked like when they maintained the thought of each picture.
Afterward, participants given instructions to either: replace the thought (“replace apple with mountain”); clear all thoughts (akin to mindfulness meditation); or suppress the thought (focus on it and then deliberately try to stop thinking about it). Replacing the thought and clearing all thoughts did appear to reduce the attentional focus on the unwanted item. In both cases, the brain signature associated with the image faded.
“We were thrilled,” said Banich in a news release. “This is the first study to move beyond just asking someone, ‘Did you stop thinking about that?’ Rather, you can actually look at a person’s brain activity, see the pattern of the thought and then watch it fade as they remove it.” But only deliberately suppressing the thought caused the brain signature to complete fade away, removing its representational shadow from the working memory system.
“Ignoring something doesn’t make it go away,” Lewis-Peacock told PsyPost. “You may be able to temporarily distract yourself from a thought by shifting attention to something else or by letting go and allowing your mind to wander. However, neither of these tactics actually remove that thought from your mind and you will continue to be influenced by it. Our study suggests that to discard a thought, one must engage with it first and only then can it be changed.”
Lewis-Peacock and his colleagues published another study last year in which they found that discarding information from the brain was associated with more mental effort than keeping it. Intentional forgetting was associated with stronger activation in sensory and perceptual areas of the brain.
The findings have important implications for understanding basic cognition, and could help in the treatment of psychiatric conditions such as post-traumatic stress disorder, which is characterized by intrusive, unwanted thoughts. But more research is needed to clarify the extent of the new findings.
“A major caveat of this ‘subtraction by addition’ method of thought suppression is that we don’t yet know whether this principle holds for personal and/or emotional information (for example, negative self-talk),” Lewis-Peacock noted. “The current study used pictures of emotionally neutral information (fruits, landscapes, celebrities). It is an open question whether emotionally valenced information can be manipulated in the same way, or whether such memories will be ‘stickier’ and thus require additional tactics to remove from mind.”
The findings also have some practical implications. “People often think, ‘If I think about this harder I am going to solve this problem.’ But work by clinicians suggests it can actually give you tunnel vision and keep you in a loop that is hard to get out of,” said Banich.
“While our thinking is influenced by many factors outside our conscious awareness, we do also have a great deal of control over what we think about,” Lewis-Peacock added. “It is important to consider not only what thoughts we entertain, but also how we entertain them. How we move from one thought to the next matters, and this is an important issue to consider in our busy lives that involve constant interruptions and our feeble attempts at multitasking.”
Read the full study: “Changes to information in working memory depend on distinct removal operations“, authored by Hyojeong Kim, Harry R. Smolker, Louisa L. Smith, Marie T. Banich, and Jarrod A. Lewis-Peacock.