Estimates of combat-related Post-Traumatic Stress Disorder (PTSD) in U.S. veterans since the Vietnam War ranges from approximately 2& to 17%. Additional studies of combat veterans of more recent wars places the range of Iraq War returnees who suffer from PTSD  between 4% and 17%. Currently, there is no one form of treatment that has been found effective in combating this disorder, but can the brain somehow be encouraged to calm itself down?

PTSD is classified as an anxiety disorder brought on as the result of witnessing a life-threatening event. The individual repeatedly re-experiences distressing memories of the event and this constant repetition eventually alters the composition of the neural networks which process traumatic memories. This memory repetition also initiates:

• Iterative learning – learning through repetition to fear the traumatic event
• Top-down activation – expecting to find a certain pattern, the brain focuses attention on finding evidence of that pattern and not processing what is actually there
• Pruning – eliminating tiny connections between neurons called synapses that don’t receive a lot of activity, further changing the structure of neural networks

Eventually, the PTSD patient is unable to distinguish between similar experiences. Minor threats to their personal safety are perceived as being on the same level as major ones which causes heightened anxiety responses.

Researchers from the Columbia University Medical Center have been experimenting with activating the dentate gyrus – a part of the hippocampus – to relieve stress in PTSD patients and those with similar anxiety disorders. The researchers inserted light-sensitive proteins called opsins into the dentate gyrus of mice models. They used light from a fiber optic strand to alternately activate and silence both portions of the dentate gyrus for three minute intervals while the mice took part in two anxiety tests.

The researchers found that stimulating the dorsal dentate gyrus – the area involved in learning – caused the mice to be more interested in investigating their surroundings, but it inhibited their ability to learn. However, when they stimulated the ventral portion – which is involved in anxiety – the animals’ anxiety levels were decreased without interfering with their ability to learn new things. The researchers also discovered that the effects could be reversed. When the they stopped activating the dentate gyrus, the mice returned to their previous states of anxiety.

From these results, the researchers concluded that there is potential for alleviating anxiety in individuals with anxiety disorders by targeting the ventral dentate gyrus with medication or deep-brain stimulation. The advantage to this kind of targeted therapy is that it makes an immediate impact on behavior and so it could work much faster than current courses of treatment.

References

Kheirbek MA, Drew LJ, Burghardt NS, Costantini DO, Tannenholz L, Ahmari SE, Zeng H, Fenton AA, & Hen R (2013). Differential Control of Learning and Anxiety along the Dorsoventral Axis of the Dentate Gyrus. Neuron, 77 (5), 955-68 PMID: 23473324

McFarlane AC, Yehuda R, & Clark CR (2002). Biologic models of traumatic memories and post-traumatic stress disorder. The role of neural networks. The Psychiatric clinics of North America, 25 (2) PMID: 12136500

Richardson LK, Frueh BC, & Acierno R (2010). Prevalence estimates of combat-related post-traumatic stress disorder: critical review. The Australian and New Zealand journal of psychiatry, 44 (1), 4-19 PMID: 20073563

Image via Oleg Zabielin / Shutterstock.