Fear And Anxiety Activate The Same Brain Circuits
Last updated: October 1, 2020
For decades, neuroscientists have theorized that fear and anxiety were distinct emotions that activated different parts of the brain.
It was thought that fear was a more basal response to an immediate threat controlled by the amygdala (considered the “fear center” of the brain). In contrast, anxiety occurred over time, was linked to the stria terminalis (BNST), and didn’t always need to be triggered by the perception of danger.
As well as many other mental health professionals, I believed fear and anxiety were the same, in that anxiety only occurs when we fear we could be in danger, and that it activates the same parts of the brain.
A study published September 21 in The Journal of Neuroscience validates our view and challenges the prevailing neuroscience theory.
The study’s researchers found that when people are exposed to a threat designed to evoke fear or an uncertain threat that produces anxiety, their brains reacted similarly, activating both the amygdala and BNST.
Alexander Shackman, a neuroscientist at the University of Maryland and senior author of the study, said they discovered this similarity when they designed an fMRI experiment he called the “low budget version of an immersive experience you might have with a good haunted house or a horror film.”
For this experiment, researchers had 99 men and women participants lie in an MRI, where they were exposed to physical, visual, and auditory stimuli designed to elicit feelings of fear or anxiety.
According to Amanda Heidt, writing for TheScientist:
“In some trials, the timing was certain, meant to emulate fear—at the end of a sequential countdown, each person received a strong electric shock, saw a disturbing image, such as a mutilated body, and heard a loud noise like a gunshot or scream. In others designed to prompt ongoing anxiety, the series of numbers was random, and there was no telling when the negative stimuli would be delivered. As controls, the researchers also had trials of both certain and uncertain timing of safety, using benign stimuli such as a picture of a chair.”
Researchers created a paradigm in which participants in an MRI machine were subjected to threats meant to stimulate either fear (certain threat) or anxiety (uncertain threat). Following a series of numbers on a screen, those in the threat trials received a strong electric shock, were shown a distressing image, and heard a loud sound. In the fear scenario, the numbers counted down sequentially and the viewer knew when to expect the stimuli. In the anxiety scenario, the numbers were presented randomly and the viewer didn't know when the stimuli would occur.
HUR ET AL., J NEUROSCI, DOI:10.1523/JNEUROSCI.0704-20.2020, 2020
“During their time in the MRI machine, participants rated their fear or anxiety on a scale of one to four at the end of each trial, and everyone experienced each of the four scenarios at least once. Throughout the experiment, participants had their skin conductance monitored and their brain activity mapped.”
Researchers discovered that both fear and anxiety produced identical brain responses. Both stimulated the amygdala and the BNST.
“Using a statistical test, Shackman and his colleagues were unable to distinguish the responses between the two regions.”
The study’s abstract states:
Results revealed that the neural systems recruited by uncertain and certain threat anticipation are anatomically co-localized in fronto-cortical regions, extended amygdala, and periaqueductal gray.
Comparison of the threat conditions demonstrated that this circuitry can be fractionated, with fronto-cortical regions showing relatively stronger engagement during the anticipation of uncertain threat, and the extended amygdala showing the reverse pattern.
Although there is widespread agreement that the bed nucleus of the stria terminalis and dorsal amygdala—the two major subdivisions of the extended amygdala—play a critical role in orchestrating adaptive responses to potential danger, their precise contributions to human anxiety have remained contentious.
Follow-up analyses demonstrated that these regions show statistically indistinguishable responses to temporally uncertain and certain threat anticipation.
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Furthermore, researchers discovered that among other regions of the brain, the cortex was more involved in processing anxiety. Shackman suggested this might stem from the brain attempting to use its cognitive power to address sustained uncertainty in the face of an unpredictable threat.
“Rather than treating fear and anxiety as two different systems, Shackman says, “there’s a reasonable chance that one kind of intervention would actually hit both and help with both.” He, along with Pomrenze and LeDoux, say they would like to see RDoC updated to reflect the growing body of evidence that shows fear and anxiety reflect similar responses in the brain rather than falling back on conclusions from animal studies carried out decades before.”
As mentioned, it’s been our contention that anxiety and fear are synonymous. We also believe one can’t exist without the other.
For instance, you can’t be anxious if you aren’t afraid (fear) that something harmful might happen. And, you can’t be afraid unless you believe (fear) something harmful might happen.
Both fear and anxiety are based on the same “threat” that something harmful might occur.
We break this down in more detail in the “What Is Fear” section in chapter 6 in the Recovery Support area.
Because anxiety and fear are synonymous, we can reduce and eliminate both by addressing the conditions that create fear (which we explain in the “What Is Fear” section).
The study’s abstract makes the following conclusions:
These observations provide a framework for conceptualizing anxiety and fear, for understanding the functional neuroanatomy of threat anticipation in humans, and for accelerating the development of more effective intervention strategies for pathological anxiety.
Here we demonstrate that its major subdivisions show statistically indistinguishable responses to temporally uncertain and certain threat. Collectively, these observations indicate the need to revise how we think about the neurobiology of anxiety and fear.
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1. Shackman, Alexander, et al. "Anxiety and the neurobiology of temporally uncertain threat anticipation." JNeurosci, 21 Sept 2020.
2. Heidt, Amanda. "Brain Circuitry for Fear and Anxiety Is the Same on fMRI." TheScientist, 21 Sept 2020.
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