How stress hormones promote the brain's building of negative memories

too much stress

Fight or Flight

What happens when you can neither fight or run?

When a person experiences a devastating loss or tragic event, why does every detail seem burned into memory; whereas, a host of positive experiences simply fade away? It's actually a little more complicated than scientists originally thought, at least according to a recent study 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. It is chemically similar to the hormone. 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, which may just make all the difference 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.

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

In her study, Segal, an assistant research professor at the Institute for Interdisciplinary Salivary Bioscience Research (IISBR) at ASU, and her colleagues at the University of California- Irvine showed that human memory enhancement functions in a similar.

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 then rated her feelings at the time she was viewing the image, in addition to giving saliva samples before and after. One week later, a surprise recall test was administered.

What Segal's team found was that "negative experiences are more readily remembered when an event is traumatic enough to 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 if we can lower norepinephrine levels immediately following a traumatic event, we may be able to prevent this memory-enhancing mechanism from occurring, regardless of how much cortisol is released following a traumatic event."

Further studies are needed to explore to what extent the relationship between these two stress hormones differ 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 in 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.