A recent study led by UNSW psychologists has mapped what happens in the brain when a person tries to suppress a thought. The neuroscientists managed to decode the complex brain activity using functional brain imaging (fMRI) and an imaging algorithm. The findings suggest that even when a person succeeds in ignoring a thought, like the pink elephant, it can still exist in another part of the brain, without them being aware of it. This suggests that mental images can form even when we are trying to stop them. Participants were given a written prompt (either green broccoli or a red apple) and challenged not to think of it. To make this task even harder, they were asked to not replace the image with another thought. After 12 seconds, participants confirmed whether they were able to successfully suppress the image or if the thought suppression failed.
Eight people were confident they had successfully suppressed the images, but their brain scans told a different story. Brain neurons fired and then pulled oxygen into the blood each time a thought took place. This movement of oxygen, which was measured by the fMRI machine, created spatial patterns in the brain. The researchers decoded these spatial patterns using an algorithm called multivoxel pattern analysis (MVPA). The algorithm could distinguish brain patterns caused by the vegetable/fruit prompts. Eight study participants were confident they had successfully suppressed the images of the red apple or green broccoli, but their brain scans suggested otherwise. The scans showed that participants used the left side of their brains to come up with the thought, and the right side to try and suppress it.
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https://medicalxpress.com/news/2020-09-neuroscience-hidden-thoughts-visual-brain.html