From the biomedical science labs, Assistant Professor Jun-Hyeong Cho, M.D., Ph.D, and his postdoctoral researcher Woong Bin Kim are manipulating suppression of memory through the use of light to limit neuron communication. This is a method commonly known as optogenetics, the use of light to weaken the synapses of a neuron.
Through the use of mouse models, both scientists were able to reduce synapses between neurotransmitters by light exposure to eradicate the memory of certain high-pitched tones associated with fear, resembling traumatic fear, compared to low pitched tones, the control group.
Developing adaptive fear depends on strengthening the connection between two nerves through developing more receptors to receive the neurotransmitter chemicals, like epinephrine, released in a neuron synapse therefore forming a rather unpleasant memory. While this is a natural process in all humans, post-traumatic stress disorder (PTSD) is known for the arousal of those fears by associating them with certain cues like troubling sound and can cause detrimental quick reactions. Reducing the interaction may erase the association and reduce some symptoms of PTSD.
In their experiments, Cho and Kim exposed mice first to a first round of high-pitched tones and low-pitched tones and recorded no abnormal responses. In the second round, they foot-shocked (a small electric shock to the feet of lab animals) half the mice when they heard the high-pitched tone. The mice reacted by freezing upon receiving the footshock.
In the third round, however, when the previously shocked mice heard just the high-pitched tone without the actual footshock, they still responded by freezing. This is due to the strengthening of the neuron interaction in the memory-forming part of the brain.
Using light, scientists can selectively weaken the interactions by decreasing the number of neurotransmitter receptors in the synapse, erasing the bad memory. This research found that fear memory can be manipulated in such a way that some beneficial memories are retained while others, detrimental to our daily life, are suppressed.
Cho also pointed out that not all fear can be erased because the brain integrates both sounds together. In order for adaptive fear to develop, the brain needs to discern between different cues and only associate it with aversive events.
The researchers claim that this will further our understanding of how adaptive fear memory is encoded in the brain based on a certain stimulus that can be artificially targeted using these methods. This research is a stepping stone for intervention to suppress symptoms of PTSD and even transform the experiment to reward learning stimuli to treat human addiction.