Unpleasant memories a thing of the past
Fear associated behaviours such as avoidance and aggression are useful in the mammal world to cope with various threats from the environment. Acquisition of fear must be followed by its extinction in humans to avoid development of anxiety disorders such as post-traumatic stress disorder (PTSD). Rodent studies demonstrated the importance of reciprocal connections between the medial-prefrontal cortex (mPFC) and the amygdala in relation to the acquisition and extinction of fear-associations. However, the amygdala-mPFC network is much more complex in primates than in rodents. The EU-funded AMY-MPFC-EXTINCTION project developed a primate model for emotional learning, using tone-odour conditioning where the subjects associate pleasant and unpleasant odours with different tonal sounds. The scientists recorded electrical stimulation from the amygdala and mPFC of awake, behaving monkeys and humans during rest. After temporary inactivation of one of the brain structures, they recorded the level of stimulation during acquisition, recall and extinction of the fear. Using this data, AMY-MPFC-EXTINCTION tracked the neural codes that underlie learning of positive and negative memories, extinction of negative memories and failure to eliminate them. Of great significance, the researchers showed they could directly manipulate the cortex-amygdala neural pathway to prevent recovery of unpleasant memories. Knowledge of mechanisms behind the pathways responsible for negative emotional learning and memory may provide the means to further manipulate neural information transfer. Prevention of return of aversive memories could lead to the development of therapy for anxiety disorders such as PTSD.
