Worse than a song stuck in your head, negative thoughts that you can’t push away can be highly detrimental to your wellbeing. Sometimes, try as we might to suppress them, some thoughts just keep coming back.
New research suggests this might be because those unwanted thoughts still exist in another part of the brain.
This finding suggests that trying to suppress repetitive thoughts as a way to give our brains a break (and protect our mental wellbeing) might not be the best strategy, supporting what classic studies had first suggested.
“These results provide new neural evidence of the pervasiveness of suppressed thoughts and unveil a network of brain areas to be targeted to treat intrusive thought disorders” such as post-traumatic stress disorder, the authors of the study said.
The study tested this with neutral thought content. The team mapped the brain activity of 15 people as they tried to suppress any thoughts or images of either a red apple or a green broccoli.
The challenge was to avoid thinking about the food item for a mere 12 seconds after the participants had been prompted to visualise it – and not replace it with another image – just to keep their mind clear.
After completing the series of tasks, eight people reported that they had successfully suppressed any thoughts or images of the fruit or veg, but their brain scans suggested otherwise.
A technique called functional magnetic resonance imaging, which detects changes in blood flow, had been measuring their brain activity. Then a computer algorithm tuned to detect the difference in patterns of brain activity corresponding to thoughts about either fruit or vegetables was used to analyse the data.
“Using this algorithm, we can see what people are imagining even when they’re not aware of it,” said cognitive neuroscientist Roger Koenig-Robert from Monash University in Australia.
The scans showed that voluntarily thinking about the two ingredients activated the left side of participants’ brains, and the right side fired up when they tried to suppress such thoughts.
“We were able to find visual representation of the thought – even when participants believed they successfully pushed the image out of their minds,” said Joel Pearson, a cognitive neuroscientist from the University of New South Wales, Sydney.
“The visual cortex – the part of the brain responsible for mental imagery – seemed to be producing thoughts without their awareness,” he added. “This suggests mental images can form even when we’re trying to stop them.”
Specifically, visual imagery-like representations of their foody thoughts persisted in the lateral occipital cortex, the part of the brain that recognises objects.
“These results suggest that the content of suppressed thoughts exists hidden from awareness, seemingly without an individual’s knowledge, providing a compelling reason why thought suppression is so ineffective,” the authors concluded in their paper.
But ‘thought suppression’ means avoiding thinking about one item, and not replacing it with another one or distracting yourself. In this case, the researchers couldn’t be absolutely sure that their 15 participants weren’t distracting themselves with other ideas to avoid thinking of apples and broccoli.
Future studies involving more people will be needed; likewise, other experiments testing what happens in the brain when people try substituting one thought with another, rather than trying to suppress a bothersome thought altogether.
Previous research from the same group, published in 2019, suggested that thought substitution is more effective than suppression for thought control.
And of course, lying in a brain scanner thinking about fruits and vegetables is a tad bit different to the worries of everyday life, or the thought patterns that emerge due to mental health issues.
But these findings are a step forward in better understanding our minds, and taking comfort in knowing just why controlling unwanted thoughts can be so difficult.
The study was published in the Journal of Cognitive Neuroscience.