As a society we are constantly stressed. We stress about finances, our families, our jobs and the daily responsibilities we must tend to. Our brains are wired to handle stress and many times the stress response can be good for us. But when stress starts to control our daily lives or when a traumatic event happens, it can become a pathological disorder such as acute stress disorder or post-traumatic stress disorder.
How trauma affects the brain
PTSD has a lifetime prevalence of 8 to 10 percent and has a higher predilection for females than for males. Many might assume that PTSD only happens to war veterans after returning from combat, but PTSD can affect anyone who has experienced a very traumatic event such as rape, asylum, a catastrophic disaster or any type of life-threatening condition. PTSD is diagnosed by a one-month history of intrusive thoughts, dreams, images or flashbacks of the traumatic event that occurred.
Studies have shown that people who have PTSD become hypersensitive to stress even when the type of stress has no relationship to the traumatic events that the person experienced. Their stress response in their amygdala becomes rewired and, as a result, they are often continually stressed about issues that normally would not induce a stressful response. The amygdala is the fear-processing center in the brain, and hormones such as norepinephrine and cortisol have been shown to have a direct impact on the amygdala and the stress response.
The startle response and prepulse inhibition
Two mechanisms that are responsible for this hypersensitive stress response are known as the startle response and the prepulse inhibition denoted as PPI.
The startle response is a natural, involuntary brainstem response to a threatening stimulus. It is initiated by the sympathetic nervous system and can return to normal very quickly after the danger disappears. “The reflex starts with the head which jerks as the neck muscles contract and the eye muscles tighten and blink. Then the response moves down into the torso which flinches; the shoulders raise and arms stiffen, the abdominal muscles contract and the chest flattens, then the knees flex — all this in around one second. Alongside these external changes, breathing and blood pressure levels change and the heart rate accelerates …”
The prepulse inhibition is a neurological mechanism in which the prestimulus, known as the prepulse, acts to weaken the actual startle stimulus, known as the pulse. When the prepulse weakens the actual startle response, the overall response to stress is decreased.
An increase in the startle response and a decrease in the prepulse inhibition lead to a stronger and more sensitive response to stress. Both of these abnormalities are seen in patients with PTSD as well as schizophrenia and other psychiatric disorders. This may explain why people with PTSD react to stress much differently than those who have not been diagnosed with this disorder.
Corticotropin- releasing factor (CRF) is responsible for the production of cortisol, a common stress hormone in the body. CRF and norepinephrine both play a pivotal role by directly acting on the amygdala through their specific receptors in the brain. Studies have indicated that experimenting with new drugs that target these stress hormones and receptors may help alleviate the hyper stress response in people who have an increased startle response and a decreased prepulse inhibition as in the case with PTSD. This research could be pivotal in treating people with schizophrenia, PTSD and anxiety disorders.
Kristen Fuller, M.D., is a senior staff writer at the Sovereign Health Group and enjoys writing about evidence-based topics in the cutting-edge world of medicine. She is a physician and author, who also teaches, practices medicine in the urgent care setting and contributes to medicine board education. She is also an outdoor and dog enthusiast. For more information and other inquiries about this article, contact the author at email@example.com.