The Present Past

Memories of emotional events, especially aversive ones, tend to attach themselves to anything around them.

—Kerry Ressler, Assistant Professor of Psychiatry, Center for Behavioral Neuroscience

Vol. 7 No. 1
September 2004

The Present Past
The science and art of memory

Memories of emotional events, especially aversive ones, tend to attach themselves to anything around them.
Kerry Ressler Assistant Professor of Psychiatry, Center for Behavioral Neuroscience

Trauma in a weird way is about the future. . . . It's the sense that it's probably going to happen again.
Angelika Bammer, Associate Professor, Graduate Institute of the Liberal Arts

Upon My Return to the Chair
Identity and academic sacred space in Middle Eastern and South Asian studies
Gordon D. Newby, Professor and Chair, Middle Eastern and South Asian Studies

Neuroscience for Bird Brains
An unconventioal frontier for understanding social behavior
Donna Maney, Assistant Professor of Psychology

The Politics of Advice
Biased scientific information in government agencies
Mike Kuhar, Charles Howard Candler Professor of Neuropharmacology

Crossing Boundaries
How intellectual initiatives form and flourish
Paul Jean, Associate Director of New Research Initiatives, Emory College Office of Research, and Daniel Teodorescu, Director of Institutional Research, Office of the Provost


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Academic Exchange: Describe your research.

Kerry Ressler: The main question I’ve been interested in is how the environment shapes the brain. How can we use hard science to understand the actual mechanisms of learning and memory, as far as that shapes who we are? My lab focuses on using molecular biology in combination with behavioral neurobiology to try to understand the molecular and cellular mechanisms of fear learning. In animal models, fear learning is a process of classical conditioning [the kind of learning Pavlov and his dogs made famous] in which a previously neutral cue, such as a light, tone, or odor, becomes paired with an aversive cue, such as a mild foot shock. After this pairing, which creates a memory that lasts for months to years, the previously neutral cue now elicits a fear reaction. We can then measure the physiological and behavioral fear response in these animals. The basic tenet that brings the two together is that we can understand in a concrete way how new learning occurs behaviorally. By doing that in a simple way in animals, we can eventually understand the structural and molecular mechanisms of learning. Many mental disorders relate to learning and memory. At one level for example, Posttraumatic Stress Disorder (PTSD) is a disorder of negative memories that are either overlearned or difficult to diminish through extinction, or are a combination of both.

One day a week, I work at Grady Hospital, mostly with people from the inner city with ptsd, which is an under-recognized phenomenon. In our clinic, the Trauma Clinic at Fulton County Community Mental Health Center, the prevalence of ptsd is as high as it is among Vietnam veterans. Interpersonal violence, gun violence, and neglect lead to a level of trauma in the inner city that can be as high as it is for people in war. And that contributes to cycles of violence.

AE: When someone is frightened, does emotion distort the process of creating the memory of that moment?

KR: The term “distortion” has implications that I would not want to evoke. But human behavioral data and animal data show that emotionally charged events lead to much stronger memory retention and memory encoding than those without emotional contexts. There’s decades of data on that. And that’s probably for positive as well as negative emotions. What we know now is that the amygdala and the hippocampus are probably acting as the hubs of memory, and they are telling the rest of the brain what’s important and what’s not.

AE: Why are you hesitant to use the word “distorted” to describe the way emotionally laden memories are recorded?

KR: Because of the political ramifications of that word: “distortion” implies it’s stretched from truth. The animal data, if anything, would argue that in these models it’s not stretched from truth, but may instead represent a hyper-aware memory that is learned in a more vivid or enduring way. Such data also suggest that emotionally laden memories may be discriminated differently than non-emotional memories.

AE: Discriminated in what way?

KR: Discrimination versus generalization refers to the ability of an organism to discriminate between any two different cues. The level at which it can distinguish between the two shows discriminative learning. If it responds to both cues, even though only one was paired with the fear stimulus, then the learning is generalized.

Having something emotionally laden makes it encoded in a way that is more clearly discriminated. But memories also are constantly being reactivated. Simply remembering a memory is probably making it in some ways plastic again. And the memories of emotional events, especially aversive ones, tend to attach themselves to anything around them. Thus some memories tend to generalize a lot quicker if they contain negative emotional contexts. Think of someone with ptsd—say, someone who is raped in an evening somewhere in an alley. Initially, they may avoid that part of town, then going out at night, then perhaps all men, or even leaving the house. The negative event has become more and more broadly associated or generalized.

AE: What’s most interesting about what’s happening broadly in this field now?

KR: With the genome sequencing, we know that 50 percent of the genes in the body are more or less specific to the brain. And the primary function of the brain is probably to allow for adaptability to the environment. Almost everything that needs to happen for us to interact with the environment requires some level of memory.

Sophistication in behavioral research is converging with sophistication in molecular biology. We can manipulate genes in specific cells, pathways, and circuits into behavioral paradigms in ways that I think will allow us in the next decade to dissect out some complex processes. Understanding how a memory that occurs in a simple animal model, like a mouse, is the first step.