Humans have been trying to 'let it go' long before Queen Elsa began singing in her icy isolation. Now that many in the world are facing their longer quarantines, it's become much harder to stop ruminating on all our fresh concerns.

A new psychology study has come at just the right time. Brain imaging and behavioural research has now revealed the three best ways to rid a thought from your mind.

When people focus on 'replacing' a notion with another, or 'clearing' their minds through meditation, researchers found brain signatures of the thought faded faster, leaving only a remnant shadow in the background.

When people focus on 'suppressing' a new thought, however, its signature takes longer to disappear, although when it finally does, its departure is more complete.

"We were thrilled," says professor of psychology Marie Banich from the University of Colorado, Boulder, about the results.

"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."

Rumination, or overthinking, is a symptom of several psychiatric disorders, including depression, anxiety, post-traumatic stress disorder (PTSD), and obsessive-compulsive disorder, and it's thought to arise from some sort of deficit in a person's working memory. 

Working memory is the part of our brains concerned with the at-hand, and it can only hold so much information, usually about three or four concepts at a time. Getting rid of irrelevant thoughts on the regular and storing relevant ones for the future is therefore essential.

Unfortunately, negative thoughts are harder to banish, but when we consciously put our minds to it, we do have some control over how the information is processed in our brains. Some mental training has been shown to clear the mind faster, others slower, and there are techniques that do not work at all.

Still, many of these results are simply based on self-reports or indirect behavioural tests. Brain imaging gives us a more objective measurement.

Previous imaging research from 2015 showed that changing the contents of your working memory activates the parietal region of the brain, where we receive and process sensory information. Clearing the contents of your working memory, however, activates the prefrontal cortex, which is involved in complex cognitive processes like decision making.

Interestingly, volunteers in this study who had more trouble controlling their inner thoughts showed greater activity in the prefrontal cortex and Broca's area, which is associated with inner speech. 

The 2015 research was conducted by several of the same authors involved in this new study and focuses on three distinct strategies for removing thoughts from your mind.

Lying down inside a functional magnetic resonance imaging (fMRI) machine, 50 participants were randomly shown pictures of famous faces, fruits, and recognisable scenes, which they actively thought about for four seconds apiece.

Creating 'brain signatures' for each one of these objects, participants were then told to either clear the thought with meditation, suppress the thought by focusing on it and then actively forgetting it, or replace the thought with another object seen in the study.

Analysing the resulting data with machine learning, researchers discovered a hierarchy of brain regions involved to varying degrees in controlling our thoughts, including the parietal and frontopolar regions, as well as the dorsolateral prefrontal, which is linked to attention and working memory.

What areas were involved in each situation and to what extent depended on the mental approach used by participants, ultimately resulting in different outcomes.

By looking at the brain's activity patterns, the team was able to show when a thought was actually removed from a person's working memory – a first for the field. 

It's still not clear exactly what is happening to all this information in the brain, but it does suggest a thought can be rapidly and temporarily removed from our working memory with the right focus of attention. It can also be more permanently removed, making room for new thoughts, through proactive mental 'interference'.

"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," says Banich. 

"The bottom line is: If you want to get something out of your mind quickly use 'clear' or 'replace'. But if you want to get something out of your mind so you can put in new information, 'suppress' works best." 

If you're studying one subject, for instance, and you need to dive into another, you might want to try suppressing your working memory first.

When it comes to mental health, suppressing long-term memories is often considered a bad thing. In cases of PTSD, as the researchers point out, it can allow trauma to simmer under the surface, thereby increasing its impact. As a result of this thinking, exposure therapy is often used to actively address and restructure certain traumatic memories, so they bear less emotional and mental weight in the long run.

These new findings, however, suggest working memory may also be targeted for therapy, although this time through suppression.

Further research needs to explore how brain signatures and cognitive operations are impaired or disrupted in those with depression, anxiety, or PTSD. But once a memory has reached consciousness and entered a person's working memory, the authors think suppression might actually be a valuable initial tool for some, "as this process allows for the complete removal of the information from mind."

In comparison, replacing or clearing a thought from working memory only takes that item out of our conscious attention. While this deactivates the item's neural signature, it still leaves the information intact.

"It may be that training an individual to shift their attention by redirecting (i.e., replacing) thought or through mindfulness techniques (i.e., clearing thoughts) could be a fruitful first step followed by training to exert cognitive control to suppress the thought, and thereby reduce its potency," the authors conclude.

"Further work will need to explore these ideas, but our results, nonetheless, point the way to potentially fruitful translation to clinical practice."

The study was published in Nature Communication.