We all know that stress can be very bad for your health, with post-traumatic stress syndrome being one of the severest expressions. Stress causes the release of cortisol in our blood stream. Cortisol is a hormone involved in many important functions in the body such as the regulation of our metabolism, regulation of blood pressure, maintenance of blood sugar levels, and it has an important immune function. Cortisol is often dubbed the stress hormone because it serves an important role in 'fight and flight' responses to potentially threatening situations. Small increases in cortisol can have very positive effects in situations where split-second decisions have to be made in order to survive. It can give that extra bit of alertness to dodge a punch or prevent a car crash, it heightens your memory temporarily, it briefly increases immunity and it even makes you less sensitive to pain.
Unfortunately, when the cortisol levels in your blood are constantly high as a result of ongoing exposure to stress, they can lead to many physical problems such as blood sugar imbalance, a decrease in bone density and muscle tissue, high blood pressure, a lowered immune system, and even impairments in your cognitive abilities such as memory and perception.
Scientists from the university of Minho in Portugal showed that the plasticity of the brain of rats under constant pressure diminished significantly. Four weeks of stress made the rats less flexible in solving problems in order to get their rewards. They would persist with one possible option and not try to explore other ways of getting their rewards, unlike their unstressed controls who would try to get to their goal in any way possible.
They did find that there is some hope though. After four leisurely weeks the rats started behaving more like the controls again, and their brains seemed to rewire too. You can read more about this research and on the New York Times website in the Science section.