Fight, flight or flick—to what extent does the human body respond to threat?

Photo by Ketut Subiyanto via Pexels.

A perceived threat, a stressful situation, or a harmful event or attack can trigger a number of physiological reactions in the body.

These responses, such as raised blood pressure, rapid breathing rate, and increased sweating, are what prepare the body to fight or flee.

New UBC Psychology research proposes that, in some situations, how the body responds to threat could be limb or side specific and is not always global or homogenous across the body.

Dr. James Kryklywy, lead author of the study and researcher in UBC’s department of psychology, developed a study to test his theory of limb-specific responses to challenge the assumption that the autonomic nervous system (ANS), which regulates body processes, such as blood pressure and breathing rates, always works globally to prepare the whole body to fight or flee.

“The result is the cleanest most beautiful data I’ve been associated with in my entire research career.”
Associate Professor, UBC Psychology

“The result is the cleanest most beautiful data I’ve been associated with in my entire research career,” says Dr. Rebecca Todd, study co-author and associate professor in the department of psychology at UBC. “We suggest that, in stressful situations, autonomic outputs can prepare either the whole-body fight or flight response, or a simply a limb-localized flick, which can effectively neutralize the threat while minimizing global resource consumption.”

“Our study investigates how the ANS responds to small scale threats — things like annoying insects, or sharp sticks that may be dangerous but may not require a full body reaction.”
Researcher, UBC Psychology

The research, Lateralization of Autonomic Output in Response to Limb-Specific Threat, was recently published in eNeuro, the Society for Neuroscience’s open access journal.

In a Q&A, Dr. Kryklywy and Dr. Todd share their research, why they challenged previous fight or flight theories, and how the study worked (hint, shocks involved).

Can you tell us about this research?

JK: This research investigated how our autonomic nervous system regulates the body’s physiological processes – e.g., blood pressure, breathing rate, and sweat glands – preparing it to fight/flee or rest and digest. It is a big component of the arousal response you make to an emotionally arousing event, such as an email in your inbox telling you that you got the job or that you are being investigated for workplace misconduct.

There has been a lot of work on how activity in the autonomic nervous system can be an index of emotional arousal, in particular how it prepares the whole body to fight or run away in response to threat. And in research on emotions, an area of interest for both Dr. Todd and myself, we often measure autonomic arousal via electrodermal activity (EDA, or sweat on the palms) to see if we have elicited a high arousal emotional state from participants. In our field we tend to assume that arousal responses to emotionally relevant or threatening events, which we measure via the skin, are global—that the response extends from the central nervous system to the skin across the body equally. If true, then when you measure electrodermal activity, the patterns you observe will be the same regardless of where you measure it. Based on that assumption, in psychology research, we don’t worry too much about where on the body we measure it or even consider the possibility that in some situations the response may be specific to a body part rather than global. Our study takes a new and different track. It investigates how the ANS responds to small scale threats — things like annoying insects, or sharp sticks — that may be dangerous but may not require a full body reaction.

RT: James’s innovative hypothesis, based on evidence mostly from researchers in computer science, is that sometimes the electrodermal skin response can be localized: If a threat is to a specific limb then the EDA response should be localized to that limb or at least that side of the body. James refers to this as the “flick” response rather than the fight or flight response. Sometimes you don’t need to run away from the bear, you just need to flick the spider away with your hand. The evidence he presents here supports that hypothesis. And by challenging the assumption that the ANS response to threat is always global, James’ hypothesis and findings challenge some of the conventional assumptions held by a lot of research in psychology.

What prompted you to test this hypothesis?

JK/RT: An interest in the potential of body-part specific EDA responses was initially inspired by research in minimally conscious people. In this population, it was found that some people are capable of making binary responses to questions by manipulating their mental state (as assessed though MRI or EEG), and also that they often showed intact autonomic responding, as assessed by EDA. We thought it would be interesting to see if people could internally generate an EDA response to an imagined threat on one side of the body or another. But before that we realized we had to establish whether we could observe a response to threat that was specific to one side of the body in the first place. At the same time, we learned that in the field of computer science, large studies that were testing out wearable EDA monitors with the goal of predicting health outcomes was demonstrating that in fact EDA was NOT a homogenous signal across the body. Rather, it can fluctuate between biases to the right and left side over the course of a day in association with the nature and intensity of arousing events encountered.

This research was taking place almost entirely independently from psychology research involving emotional arousal responses and so was free of many of the assumptions guiding psychology research. Because computer scientists were coming at the research from a fresh angle, they were able to identify the existence of lateralized EDA signals in the first place. But while this research indicated that we can measure unbalanced EDA on different sides of the body, it didn’t answer any questions about what the functional reason for its development would be, given what we know about the role of the ANS, which is that it is key for metabolic conservation/mobilization. We set out to test whether lateralized bias in EDA occurred in response to limb-localized threat (which would be a consistent function to its canonical role), thereby providing a potential future avenue to exploit in future clinical applications.

How did the study work?

JK/RT: In this study, we administered mild electrical stimulation to either the right or left forearm, while recording EDA bilaterally. We then compared the strength of EDA signal between recording sites on any given trial to assess for ANS lateralization bias.

What does this research reveal about our fight, flight, or flick response?

JK/RT: We found that there is indeed an enhanced ANS response on the threatened side. This is interpreted as preparing the body for a response that may not require the whole body. Not all threats need us to fight or flee to be safe…sometimes we can flick. With the “flick” response, instead of recruiting resources to prepare the whole body for fight or flight, it recruits them maximally only in the side of the body or the limb that is threatened so that it can deal with the problem with a flick. This appears to be much more efficient mechanism to address threat, as it conserves metabolic resources in the parts of the body unnecessary for the response.

Dr. James Kryklywy performed this research as a post doctoral research fellow in Dr. Todd’s Motivated Cognition Lab. He joins Lakehead University as Assistant Professor in January 2023.