Tracking exactly how a brain can forgot a piece of information, and what that means for patients living with neurocognitive disorders, has been revealed through new research.
The mechanisms by which people remove information from their working memory have been identified in a study, which it is hoped can help inspire better attention and focus, but also look at clinical targets for helping people living with conditions including depression, PTSD and ADHD.
“It may sound surprising that people can control what and how they forget,” says Marie Banich, of the University of Colorado, Boulder.
“But control over working memory is critical for switching between and re-prioritising 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.”
Banich became interested in understanding forgetting after losing someone to suicide. The experience got her thinking about the dangers of intrusive thoughts for people suffering from depression and related disorders.
“The content that gets stuck in mind varies across different disorders,” Banich explains.
For example, people with schizophrenia may be consumed with paranoid thoughts, while those who have obsessive compulsive disorder might be worried about germs, and someone with anxiety may get stuck thinking about bad things that might happen in the future.
“But it’s the same process,” she says. “The thoughts are going round and round, becoming the focus of attention and difficult to remove.”
Complicating the treatment of these disorders is the fact that so many rely on self-reporting of symptoms, and even if a patient reports improvement, they may still be negatively ruminating.
That challenge led Banich, a trained cognitive neuroscientist, down a path to answer the question: How can we know whether somebody has really stopped thinking about something?
Step by step, Banich and her colleagues have been learning how to track what happens when someone tries to purge a thought from their mind.
Their latest work builds upon their past 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, or clearing their mind of all thoughts.
This seemingly simple framework has taken many years of work, with the help of fMRI imaging, machine learning, and other technological and experimental advancements.
It started, Banich said, with the realisation in the middle of one night that “we can actually use neuroimaging to verify that somebody stopped thinking about something.”
Asking participants to think about information in different categories (e.g. faces, places, fruit) while in the fMRI scanner, Banich and her team first trained a computer on the resulting neural patterns for the categories and examples from each.
They then asked study participants to forget information in different categories, verifying whether it was removed by tracking whether the brain pattern was still present.
They also identified the neural pattern of brain activation associated with each of the three mechanisms of forgetting – whether they replaced the thought of a face like Emma Watson, with an object, like the Golden Gate Bridge, suppressed the memory of Emma Watson, or cleared all thoughts.
Through this work, they have identified four brain networks that distinctly activate whether the 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.
Their work suggests that when the brain suppresses a thought or clears thoughts entirely, the frontoparietal control network likely plays a prominent and distinct role.
“Can we get some metric of people who might have difficulty controlling their thoughts?” Banich asks.
“Maybe the frontoparietal network in people who are having difficulty controlling their thoughts can’t differentiate between those mechanisms, or in them they are all muddled together?”
In future work, Banich and her colleagues will also be looking at whether they can use biofeedback while participants are in the fMRI scanner to see if that can aid individuals in controlling the mechanism for removing unwanted information.
In identifying these specific brain networks, the research offers a path forward for investigating potential differences among individuals in how they forget.
An important part of this work has been looking at “proactive interference,” which can happen when the brain is trying to learn something new that overlaps in category with something already in mind – like trying to learn Emma Stone’s face instead of Emma Watson’s.
The takeaway from Banich’s work has been that, in part due to proactive interference, suppressing a thought is more efficient than replacing it.
