Brain Scans Show How Suppressed Thoughts Still Lurk Deep In The Brain


Tom Hale

Tom is a writer in London with a Master's degree in Journalism whose editorial work covers anything from health and the environment to technology and archaeology.

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If you’re given the command “don’t think of a pink elephant,” you’ll find it fiendishly difficult to not conjure up this image in your mind for a brief moment. But it turns out, even if you think you’ve managed to suppress this thought, it still exists in another part of your brain without you being aware of it.

This curious insight into the murky world of unconscious thought is the main finding of new research by psychologists at the University of New South Wales (UNSW) and Monash University in Australia. 


Published in the Journal of Cognitive Neuroscience, the new study used brain scans and an imaging algorithm to decode complex brain activity to understand how the human mind suppresses thoughts. For the study, 15 people were given a written prompt of an object, such as green broccoli or a red apple, and were challenged to not picture it in their mind. Meanwhile, their brain activity was being scanned by functional magnetic resonance imaging (fMRI) and an imaging algorithm.

After 12 seconds of mulling, they were asked whether or not they believed they had successfully suppressed the thought of the image. Although the majority of participants said they believed they had successfully suppressed the visual thought, their brain scans said otherwise. 

“The visual cortex – the part of the brain responsible for mental imagery – seemed to be producing thoughts without their awareness,” Professor Joel Pearson, senior author on the study and professor of cognitive neuroscience at UNSW Science, said in a statement.

The algorithm was able to specifically pinpoint the brain activity that was associated with thoughts of, for example, the red apple. Using this, the team showed that the left side of their brains was fired up when they were having visual thoughts of the object, while parts of the right side were sparked when attempting to suppress it. Even if the participants said they did not think about the object, it appears the thought still lurked in their brain activity. 


This finding fits nicely with another discovery made by the same team last year that looked at peoples’ ability to suppress a visual thought. The study from 2019 found that people who appear to be good at suppressing certain thoughts still harbor traces of the thought in their unconsciousness. Thanks to this new study, the researchers believe they have honed in on how this peculiar process might unfold. 

“We know that you can have conscious and unconscious perception in your visual cortex – for example, I can show someone an image of a spider, make the image invisible, but their brain will still process it,” added Professor Pearson. 

“But until now, we didn’t know this also worked with thoughts.”


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