Modification of Emotional Connections

    Post-traumatic Stress Disorder (PTSD) and similar conditions such as depression and anxiety have a significant impact on people’s daily lives around the world.  PTSD, specifically, often is correlated with strong emotional connections to an event.  This connection can be extremely strong, and people often report total submersion into the memory of the event during an episode.  The root cause for the distress and cause of dysfunction in daily life is the emotional response when triggered back to the event.  The ability to remove these memories, or alter the emotional attachment to them, would be a significant step forward in the treatment of psychiatric disorders.

    Researchers are working on such an ability with the development of optogenetics.  This invasive medical procedure allows for extremely targeted modifications in synaptic strength.  Previously, researchers have been able to implant false memories into mice by tagging neurons of memory-engram regions in the mice’s hippocampus that were activated during a fear context.  They then later activated these neurons in a different context and elicited a fear response from the mice.  Perhaps more interestingly, researchers were also able to deactivate and then later reactivate memories.  This was done through optogenetic stimulation in the lateral amygdala.  The memory was deactivated via long-term depression which had disturbed the associative memory created earlier.  Researchers were then able to recover the memory via long-term potentiation the following day.  Impressively, researchers have been able to do repeat these results with well-established memories in mice by inhibiting CA1 hippocampal neurons when exposing the mice to a cue established over four weeks prior.  Similarly to the research done prior, these effects were temporary and reversible via stimulating the neurons in the CA1 hippocampus.  There are more possibilities with optogenetics than simply turning memories on and off, they can be manipulated as well.  We are capable of making valence modifications to memory, such as turning a sad one to a happy one.  This does not alter the memory itself but alters our emotion connected with it.  When we recall a memory engram, which is encoded in the hippocampus by the dentate gyrus, the valence of an elicited response could be altered through reassociation with a new unconditioned stimulus of an opposite valence.

    Emotional responses to stimuli studied by Dr. Foci, in his work “Differentiating neural responses to emotional pictures: Evidence from temporal-spatial PCA”, may have a unique connection to the future of optogenetic studies.  We consistently have emotional responses to the stimuli around us, and this may become highly taxing on those in high-stress work environments such as doctors and soldiers.  By targeting and flagging specific neurons, we may someday be able to turn on and off the emotional component of our connection to the world around us.  This may be highly beneficial for those who suffer from PTSD and similar anxiety disorders who may suddenly become overrun with emotion due to a triggering event.  Optogenetics may play a helpful role in psychiatric treatment through memory modification and through valence modifications in order to preserve memories but reverse negative emotional aspects of them.

https://link.springer.com/article/10.1007/s11569-020-00377-1