Stress . . .

That Squeezing Feeling!

Stress Hormones And How They Promote Negative Memories

Most of us have heard of the body's stress response, fight or flight, short for HPA Axis (hypothalamic-pituitary-adrenal axis) and the sympatho-medullary Adrenal system. But what happens when you can neither fight nor run?

When a person experiences a stressful or traumatic event, e.g. devastating loss or tragic event or natural or unnatural phenomena, why is it that every detail seems to be forever burned into memory; whereas, a host of positive experiences simply fade away? It turns out, it's actually quite a bit more complicated than scientists had originally thought. This is the view taken in a recent study that was published in the journal Neuroscience, by Arizona State University, researcher Sabrina Segal.
When people experience a traumatic event, the body releases a few major stress hormones: norepinephrine/noradrenaline, epinephrine/adrenaline and cortisol. Epinephrine boosts heart rate and blood pressure, while norepinephrine mobilises the brain and body for action during the fight-or-flight response. Cortisol plays a role in the mobilisation and efficient usage of glucose in the brain and body. Levels of these hormones are elevated when individuals feel threatened or experience highly emotional reactions. Of course, there is an awful lot more going on but these neurochemicals are the major players.

In the brain, norepinephrine functions as both a neurotransmitter, as well as a neuromodulator, chemical messengers that can also enhance memory. Memory, of course, is a major part of the stress system, as it helps the brain to make very important decisions/responses much more quickly. And this may just make all the difference you need in life or death decisions? Unfortunately, the dysfunction of these systems becomes a major contributor to anxiety disorders!

Research on cortisol has demonstrated that this hormone can also have a powerful effect on strengthening memories. However, studies in humans up until now have been inconclusive -- with cortisol sometimes enhancing memory while at other times having no effect.

Whether cortisol has an effect on strengthening certain memories, may rely on the activation of norepinephrine during learning, a finding previously reported in studies with rats.

Segal, an Institute for Interdisciplinary Salivary Bioscience Research at ASU assistant research professor and her University of California- Irvine, colleagues showed that human memory enhancement functions in similar ways.

Conducted in the laboratory of Larry Cahill at U.C. Irvine, Segal's study included 39 women who viewed 144 images from the International Affective Picture Set. This set is a standardized picture set used by researchers to elicit a range of responses, from neutral to strong emotional reactions, upon view.

Segal and her colleagues gave each of the study's subjects either a dose of hydrocortisone -- to simulate stress -- or a placebo just prior to viewing the picture set. Each woman rated feelings at the time of viewing the image and gave saliva samples before and after. One week later, a surprise recall test was administered.

Segal's team found that "negative experiences are more readily remembered, if traumatic events release cortisol after the event, and only if norepinephrine is released during or shortly after the event."

"This study provides a key component to better understanding how traumatic memories may be strengthened in women," Segal added. Because it suggests that lowering norepinephrine levels immediately following a traumatic event may help prevent this memory-enhancing mechanism occurring, regardless of how much cortisol release follows a traumatic event."

Further studies are needed to explore to what extent the relationship between these stress hormones differs, depending on whether you are male or female. Particularly because women are twice as likely to develop disorders from stress and trauma that affect memory, such as post-traumatic stress disorder (PTSD). In the meantime, the team's findings are the first step toward a better understanding of neurobiological mechanisms that underlie traumatic disorders, such as PTSD.




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