Researchers from RIKEN Center for Brain Science identified a pathway in the brain linked to fear extinction.
Human beings develop conditional responses when they experience strong negative emotions. It is observed that individuals experience less fear over time as the conditioned stimulus such as music is dissociated from the fearful experiences .This phenomenon is called fear extinction. Absence of fear extinction can lead to anxiety disorders such as post-traumatic stress or phobias.
The team of researchers from RIKEN performed a series of experiments on lab rats to understand brain regulations to both the normal and psychological situations. The study reported that to extinguish fear an animal needs to recognize when an expected fearful event does not happen. The team scanned the ventral tegmental area (VTA) of brain for dopamine neurons as they are known to be active when expected unpleasant events don’t happen. The lab rats were subjected to specific sound with an aversive experience. In this case it was a mild foot shock. The rats began behaving as if they were threatened as the sound started playing without the foot shocks. However, the rats could not unlearn the fear response when VTA dopamine neurons were silenced just after playing the sound. It proves that without VTA dopamine activity at that specific time, the mental link between the sound and the shock could not be removed. Some VTA dopamines are connected to brain regions known to store extinction memories while others are related to reward learning. Researchers blocked both these paths separately through Optogenetics to reveal that both paths affected fear extinction however, in opposite ways. Blocking the reward pathway prevented fear extinction, while blocking the other pathway enhanced it. Psychiatric conditions such as anxiety disorders can be cured by targeting the dopamine systems combined with exposure therapy. The research was published in the journal Nature Communications on June 27, 2018.