Your brain may need a break from negative thinking.

If you have ever replayed an awkward conversation from three years ago while brushing your teeth, your brain may be doing more than simply being dramatic.

Researchers are increasingly interested in what is called repetitive negative thinking, or RNT, which includes repeatedly worrying about the future or ruminating about the past. A 2020 study led by researchers at University College London examined 292 adults aged 55 and older and found that higher levels of RNT were associated with greater cognitive decline over four years, including changes in memory. Among participants who underwent brain imaging, higher RNT was also associated with greater deposits of amyloid and tau, proteins associated with Alzheimer’s disease. 

That sounds alarming, but there is an important catch. The research shows an association, not proof that negative thinking directly causes Alzheimer’s or that every stressful week is secretly shrinking your brain. Dr Natalie Marchant, an Associate Professor at University College London and Principal Investigator of the Marchant Lab, has described RNT as a potentially modifiable risk factor and developed the Cognitive Debt hypothesis to investigate how persistent negative thought patterns might contribute to vulnerability to Alzheimer’s disease. The researchers themselves note that the relationship could potentially work in the other direction too, with early changes in the brain encouraging more worry. In other words, your brain is complicated and unfortunately does not come with a simple “stop worrying” button. 

The encouraging part is that your mental habits are not necessarily fixed in concrete. Research from UCL involving 1,281 people with meditation experience found that longer meditation experience was associated with lower levels of repetitive negative thinking, while greater self-compassion was also linked with less RNT. The findings do not prove that meditation prevents dementia, but they provide an interesting reason to give your mind a little breathing room. Marchant has also pointed to mindfulness and cognitive behavioural therapy as approaches worth investigating for reducing repetitive negative thinking. 

So, if you catch yourself spending an hour mentally arguing with someone who is not even in the room, try changing the channel rather than letting the thought loop run indefinitely. You can practise mindfulness, challenge unhelpful thoughts through cognitive behavioural techniques, stay physically active and maintain social connections, all of which are relevant to broader brain health.

The goal is not to force yourself to be relentlessly positive, because that would be exhausting too. It is simply to notice when your mind gets stuck in the same negative groove and learn how to step out of it. Your brain has enough work to do without making it attend the same argument every night.