A study published in Nature by researchers from the University of California has uncovered a novel way to treat conditions stemming from fearful memories. This can assist in preventing extreme fear reactions like anxiety, depression, and freezing in people with mental health conditions like post-traumatic stress disorder (PTSD).
PTSD arises from witnessing or experiencing a traumatic event. People with this condition often have nightmares or flashbacks, making it feel as though they are experiencing the event anew. This causes extreme anxiety and fear, which disrupts sleep and daily life.
Previous studies have found that the amygdala, hippocampus and prefrontal cortex are responsible for processing fear responses. However, the current study in mice shows that the prefrontal cortex plays a larger role in storing and processing these fear memories.
The findings suggest that fearful memories are stored in nerve connections of the prefrontal cortex. “We expect the results will contribute to developing a more effective intervention in PTSD and other fear-related disorders,” said Dr Jun-Hyeong Cho, associate professor of molecular, cell and systems biology, in a statement.
Dr Cho and his team initially exposed the mice to a fearful event (conditioned stimulus) in a modified environment (the ‘context’) to discover the role of the prefrontal cortex. The mice believed the environment caused the event. A month later, the mice froze in response to the same environment, indicating recollection of their prior experience. Researchers also noted the activation of nerve cells in the prefrontal cortex that formed strong connections with other memory nerves.
The team tested the hardwiring of these memories in the prefrontal cortex by placing the mice in a similar environment but with their nerve cells blocked. They noted that the mice could not recall their fear memory. One cause of fear-related conditions is the brain’s inability to store traumatic events as memories, thereby triggering fresh fearful responses each time similar events occur. The researchers conjectured that the understanding of this mechanism could be manipulated and used to reduce such fear reactions.
The researchers tested their hypothesis by making the mice forget the fearful event by repeatedly exposing them to the environment. This reduced the mice’s fear reaction over time, indicating that reinforcing the memory of the past fearful event as one that is finished can prevent extreme reactions like anxiety, fright and freeze. “Interestingly, the extinction of remote fear memory weakened the prefrontal memory circuits that were previously strengthened to store the remote fear memory,” said Dr Cho in the statement.
The team plans to weaken the fear memory pathway to determine if this affects the memory of the event. “Considering that people with PTSD suffer from fear memories formed in the distant past, our study provides an important insight into developing therapeutic strategies to suppress chronic fear in PTSD patients,” said Dr Cho.
