Post-traumatic stress disorder is a form of mental illness that occurs when one suffers or witnesses a traumatic experience causing them to have nightmares, flashbacks, and can also lead to anxiety or depression. PTSD is common among veterans who have served in active duty, a study conducted in 2017 found 12.9% of veterans were diagnosed with PTSD almost doubling the 6.8% of the United States population diagnosed with the disorder1. PTSD symptoms vary from person to person creating difficulties for individuals to understand what they are going through. An interview between Dr. Call and the wife of a veteran (Shelly), whose husband suffers from PTSD shows the common struggles of receiving treatment and the disorders complexities2. Shelly expresses her husband’s frustration in seeking out treatment and guidance from a military mental health clinic but was denied any form of care. This occurred even during an instance where he experienced a panic attack and was told to return home and rest. After numerous visits to the clinic, he was diagnosed with PTSD and was able to receive treatment to improve his symptoms. This veterans experience is not unique, many others are denied any form of help due to the differences in the expression of PTSD. It is important for us as a society to further understand this disorder and its severity.
A study which expresses the neuronal mechanisms of emotion and stress was conducted by Stephanie Grella during her time at Boston University, “Artificially enhancing and suppressing hippocampus-mediated memories”3. Grella and her team’s research manipulate the ventral and dorsal hippocampus with optogenetics and chemogenetics to drive context-specific behaviors. The two regions of the hippocampus have different ways of driving emotion and cognition, the dorsal region processing spatial, temporal and other framework details while the ventral region is directly linked to emotion and stress. The initial procedure includes injecting a mix virus of AAV9-c-Fos-tTA and AAV9-TRE-eYFP into the dentate gyrus of adult mice to express the c-Fos gene to enhance response to stimuli. The mice were fear conditioned in a chamber where they would receive foot shocks and then returned into the same environment the following day without the fear stimulus. Changes were found within the dentate gyrus where dorsal and ventral regions were activated with the presence of the fear stimulus, but only the ventral region was activated when the mice was returned to the fear environment.
The following procedure includes the use of optogenetic stimulation of tagged cells along the longitudinal axis of the hippocampus to drive fear or appetitive behaviors. The mice were placed into a neutral, fear, or female exposure stimulus to compare. The manipulation of these memories within the fear stimulus have expressed fear related behaviors within the mice exhibiting location avoidances and preferences. Next, the mice were split into two fear stimulus groups receiving 1 foot-shock and stimulation of the ventral DG or 4 foot-shocks and stimulation to the dorsal DG. Mice receiving 4 shocks produced suppression in freezing while those receiving 1 shock produced and increase in freezing. Finally, the chemogenetic inhibition of the basolateral amygdala within both groups receiving stimulation to the ventral or dorsal DG. When BLA cells were inhibited, there was a disruption of stimulation-induced enhancement when the ventral DG received persistent stimulus. Only within the ventral DG group there was an overlap between BLA cells active during recall of the fear memory and during the encoding of the memory.
The ability to manipulate and observe how fear memories are encoded and recalled can provide the foundation of a greater understanding for stress-related psychological disorders such as PTSD. These findings provide the specific locations where fear memories are generated and how location can trigger these memories to resurface. This can allow the formulation of more effective medications and new organizations of psychotherapy mechanisms.
References
1. PTSD and Veterans. Hill & Ponton, P.A. April 16, 2025. Accessed April 28, 2025. https://www.hillandponton.com/resources/veterans-statistics-ptsd/#:~:text=In%20a%202017%20study%20involving,any%20point%20in%20their%20lives.
2. Call J. PTSD in the military: An interview with a military wife. Psychology Today. January 2009. Accessed April 28, 2025. https://www.psychologytoday.com/us/blog/crisis-center/200901/ptsd-in-the-military-interview-military-wife.
3. Chen BK, Murawski NJ, Cincotta C, et al. Artificially enhancing and suppressing hippocampus-mediated memories. Current Biology. 2019;29(11). doi:10.1016/j.cub.2019.04.065
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