Scientists have identified a key chemical within the ‘memory’ region of the brain that allows us to suppress unwanted thoughts, helping explain why people who suffer from disorders such as anxiety, post-traumatic stress disorder (PTSD), depression, and schizophrenia often experience persistent intrusive thoughts when these circuits go awry.
We are sometimes confronted with reminders of unwanted thoughts — thoughts about unpleasant memories, images or worries. When this happens, the thought may be retrieved, making us think about it again even though we prefer not to. While being reminded in this way may not be a problem when our thoughts are positive, if the topic was unpleasant or traumatic, our thoughts may be very negative, worrying or ruminating about what happened, taking us back to the event.
“Our ability to control our thoughts is fundamental to our wellbeing,” explains Professor Michael Anderson from the Medical Research Council Cognition and Brain Sciences Unit at the University of Cambridge. “When this capacity breaks down, it causes some of the most debilitating symptoms of psychiatric diseases: intrusive memories, images, hallucinations, ruminations, and pathological and persistent worries. These are all key symptoms of mental illnesses such as PTSD, schizophrenia, depression, and anxiety.”
Professor Anderson likens our ability to intervene and stop ourselves retrieving particular memories and thoughts to stopping a physical action. “We wouldn’t be able to survive without controlling our actions,” he says. “We have lots of quick reflexes that are often useful, but we sometimes need to control these actions and stop them from happening. There must be a similar mechanism for helping us stop unwanted thoughts from occurring.”
