Researchers at The Hospital for Sick Children, Toronto, have established that stress alters how our brain forms and recalls memories. Their study may offer hope in understanding post-traumatic stress disorder (PTSD) and serving as a potential pathway to healthy memory functions.
Stress can affect memories in different ways. For example, if someone makes a mistake in a presentation, they will feel nervous in future presentations as their brain links the stress to the next event. This form of stress connects to only one memory. On the other hand, traumatic events, such as violence or overall anxiety, may spread from an initial stressful event to others. It is scientifically identified as “stress-induced aversive memory generalization.” An innocuous event- a firework explosion or a car backfiring, for example- prompted unwanted, fearful memories. The response can disrupt daily life, worsening mental health in people with PTSD.
In a recent study in the journal Cell, Drs. Sheena Josselyn and Paul Frankland, along with their colleague Dr. Matthew Hill of the University of Calgary, discuss biologists of memory generalization and a possible cure to help people with PTSD.
Josselyn says a little stress is useful – it gets us up in the morning. Too much is bad for us. People with PTSD are frequently afraid when there’s no reason to be afraid. Their study shows how that fear might be confined to particular memories and prevented from generalizing.
Using a preclinical model, the researchers tested their hypothesis. They exposed subjects to mild stress before an event that would induce fear, a model that simulated symptoms of PTSD. In all, they studied the brain’s memory engrams- physical representations of memories. Normally small, these become larger with stress and can trigger fear in safe situations.
They discovered that stress triggered the endogenous brain chemicals called endocannabinoids, which caused interference in memory. The chemicals worked on neurons in the amygdala, or the brain’s emotional center, which otherwise helps to restrain the size and specificity of memories. However, the endocannabinoids released too many, causing engrams to grow more general and larger in memory.
The researchers blocked the spreading of fearful memories by stopping the endocannabinoid receptors from working on certain neurons. This may help in lessening some symptoms of PTSD.
As the research team continues with their study, they hope to understand more about the impact of stress on both negative and positive memories. They also want to use this knowledge to enhance the therapy for psychiatric disorders.
ANI
