ASU researcher shows how stress hormones promote brain's building of negative memories

July 23, 2014

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 a bit more complicated than scientists originally thought, according to a study recently published in the journal Neuroscience by ASU researcher Sabrina Segal. Cortisol 3D Download Full Image

When people experience a traumatic event, the body releases two major stress hormones: norepinephrine and cortisol. Norepinephrine boosts heart rate and controls the fight-or-flight response, commonly rising when individuals feel threatened or experience highly emotional reactions. It is chemically similar to the hormone epinephrine – better known as adrenaline.

In the brain, norepinephrine in turn functions as a powerful neurotransmitter or chemical messenger that can enhance memory.

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 at ASU, and her colleagues at the University of California-Irvine showed that human memory enhancement functions in a similar way.

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 Posttraumatic Stress Disorder (PTSD). In the meantime, the team’s findings are a first step toward a better understanding of neurobiological mechanisms that underlie traumatic disorders, such as PTSD.

Margaret Coulombe

Director, Executive Communications, Office of the University Provost


'Ecology Explorers' bring environmental education to low-income communities

July 24, 2014

It's 4 o’clock in the afternoon and about 10 three- to eight-year-olds are seated around a table listening to Ecology Explorers intern Alexis Roeckner present a lesson about sustainability. Roeckner holds up a picture and asks: ”What is this?” Opinions abound; voices ring out left and right, sometimes with funny interpretations of the photo. From the back of the group, one timid voice says, “It’s for wind.” All faces turn toward the speaker, one of the smallest boys in the room. It is the right answer. Roeckner confirms that the object in the photo is indeed a wind turbine and explains its function to the energetic little children.

For Roeckner it is just another teaching moment in the Homeward Bound after-school program. Yet this is not a typical school-based, after-school program. As an organization, Homeward Bound provides transitional housing, employment services and other forms of support to low-income families with children that are homeless, recently evicted or fleeing a domestic violence situation. The after-school program is located in a residential community run by Homeward Bound where children live with their mothers. The program is one of Homeward Bound’s efforts to provide educational enrichment to children in this community, which isn’t well-served by typical science, technology, engineering and mathematics (STEM) programs, in part because the community’s population is very mobile. Download Full Image

The Central Arizona-Phoenix Long Term Ecological Research's (CAPLTER) K-12 education program, Ecology Explorers, started working with Homeward Bound in fall 2013. Ecology Explorers interns, student workers and graduate fellows designed and delivered lessons to groups of 10-15 children four times a semester, overseen by Ecology Explorers staff member Gina Hupton.

During the fall, lessons focused on urban ecology and urban microclimates, while the spring lessons ranged from understanding the water cycle to considering the effect pollution has on the environment. Hupton explains that the lessons were meant to provide a foundation for future learning in academic classrooms, as well as to help the children understand and appreciate the environment around them.

Lauren Gault, an Arizona State University undergraduate student working with Ecology Explorers, agrees with Hupton. “Young children still find much of the scientific world to be magical and mysterious. Exposing them to science early and often is essential to making science more accessible, more influential on their thinking and less enigmatic,” she explains.

The benefits of the Homeward Bound program extend to the ASU students who have worked with the children over the past year. Roeckner, for example, is considering an education-oriented career, thanks to the experience that she had delivering environmental education to groups like Homeward Bound during her internship. Gault, who is majoring in conservation biology and ecology with concentrations in sustainability and public policy, would like to focus on research, policy and education. She recognizes the considerable power of science education and communication in shaping a sustainable future.

Ecology Explorers will continue providing environmental education lessons to children at the Homeward Bound after-school program during the next school year. However, it will likely be to a different group of children, as families typically leave the program after mothers secure employment and housing outside the Homeward Bound community. Nonetheless, it will be another chance for Ecology Explorers student interns to take a small step toward educating the next generation of environmentally-aware citizens.

The Central Arizona-Phoenix Long Term Ecological Research project, a part of ASU's Julie Ann Wrigley Global Institute of Sustainability, examines the effects of urbanization on a desert ecosystem and vice versa through interdisciplinary projects integrating natural sciences, social science and engineering.

CAPLTER project manager Marcia Nation authored the article for a recent edition of LTER Network News.

Director of Strategic Marketing and Communications, ASU Local