- Published: November 7, 2012
Stressful incidences have been proven to have a profound impact on the brain. They may distort one's perception or memories of an event, as Oyarzún and Packard describe in their article, “Stress-Induced Gist-Based Memory Processing: A Possible Explanation for Overgeneralization of Fear in Posttraumatic Stress Disorder” (July 2012). In their study on acute stress and memory formation, Oyarzun and Packard tested the effect of stress on the brain. More specifically, they asked if catecholaminergic hyperactivity —defined as the overproduction of catechol amines, or neurotransmitters like epinephrine and norepinephrine that are released as part of the stress response—changes neural processing so that phasic neural activity increases? To test this, the authors presented emotional scenes to induce acute stress in participants. They measured neural response using an fMRI, measured pupil response and endocrine response, and they tested the subjects’ memory after 24 hours. Their results showed that subjects under acute stress had less specific memory representations and that subjects overgeneralized what they saw. This type of response correlated with increased pupil dilation (shown to measure the activity in the locus ceruleus-centered norepinephrine system) and decreased subsequent memory effects (SMEs) in the hippocampus and midbrain—meaning that there was a neurological indicator that their memories were encoded less effectively.
Why do we care about the decline in memory in the field of neurolaw? One important example is that of police officer testimony after an OIS, or officer-related shooting, where an officer must shoot an armed person. One article that examines this phenomenon was released by the FBI in their law enforcement bulletin: “Working Toward the Truth in Officer-Involved Shootings: Memory Stress, and Time” (May 2012). Prior research shows that officers interviewed six years after an OIS reported perception changes surrounding the event, where they see the incident in slow motion or fast speed. Furthermore, 46% of them reported memory loss. In the authors’ study detailed in the article, officers in the Richland County Sheriff’s Department of South Carolina underwent a live-fire simulation of a school shooting or terrorist attack. Group A was asked to give a detailed debriefing of the incident immediately afterward, and they recounted the experience again three days later. Group B only wrote a report after three days. Accuracy of subjects’ memories was determined based on a scoring system that gave points for the number of variables remembered, and variables were divided into two categories: threat variables (e.g. weapon description and subject description) or environmental variables (e.g. location, team members, etc).
The results were as follows: Group A had higher averages scores than those in Group B (whose average score was a 6.4), and the average score of Group A improved from a 7.5 immediately after the event to a 7.8 three days later. Thus, their memories seemed sharper if asked to recount the incident right after. However, the subjects’ ability to remember varied depending on the type of variable. Threat variables had a score of 4.4 right after the event, but they declined to a score of 4.2 3 days after the event. In contrast, subjects’ ability to remember environmental variables increased .2 points after the three days.
This experiment has important implications for when one should interview an officer after an OIS. It seems advantageous to ask about threat-related information (such as descriptions about the shooter) as soon as possible. Also, officers are better able to identify threat-related information rather than environmental information in a high stress situation. This trend makes sense in the context of Oyarzún’s and Packard’s study, which states that the brain must focus on what is most important for survival at the time. The current policies about when one should ask an officer to give a report are conflicting, according to the researchers. Generally, eyewitnesses and suspects are interviewed immediately afterward, whereas officers are asked to wait a day in order to recover from the traumatic event. Perhaps the best strategy would be to interview everyone immediately afterward about threats during the event, and then a day or so afterward about details in the surrounding area. At any rate, members of the legal system should not take testimonies of anyone—whether they are bystanders, suspects, or law enforcement officials—as absolute truth. While the intentions of the witnesses may not be to deceive, the brain cannot help but alter one’s memories in a stressful situation. A more detailed neurological study would be interesting to follow-up the FBI’s report, which could use fMRI to measure neural activity in officers immediately after the live-fire stimulation, as well as several days later.
Oyarzun & Packard (2012). Stress-Induced Gist-Based Memory Processing: A Possible Explanation for Overgeneralization of Fear in Post-traumatic Stress Disorder. J. Neurosci, 32(29):9771–9772.
GP Alpert, J Rivera, L Lott (2012). Working Toward the Truth in Officer-Involved Shootings: Memory Stress, and Time. US Department of Justice: Federal Bureau of Investigation. FBI Law Enforcement Bulletin, 81(5): 1-7.