Does the brain control the heart or is it the other way around? Does chronic fight or flight cause people to make bad decisions? This is a critical topic for patients with chronic pain. Let’s dig into some new research that upset what we thought we knew about how the brain works.
Tachycardia means rapid heart rate. In a specific type of neck injury called Cranial Cervical Instability, tachycardia is common. It’s believed to happen when the vagus nerve, which acts as the brakes for the heart, gets irritated by unstable C1 and C2 upper neck bones.
Fight or Flight
There are primitive lower brain functions hardwired into all of us. One of those is called the “fight or flight” reflex. This happens when we’re presented with a situation where we have two immediate choices – fight off an attacker or flee. This is associated with rapid heart rate, pupil dilation, cold hands, and feet and is also called sympathetic activation or heightened arousal. This reflex is only ever meant to be activated for short bursts. However, in some patients, especially those in chronic pain, this reflex gets chronically activated (2).
Does the Brain Control Everything or Does It “Go with the Flow”?
We’ve all been taught that the brain controls every aspect of your body and reality. However, we also know that some things in the body just happen automatically. For example, we know that walking is controlled by circuitry in the spinal cord. We also know that the heart will still beat without a brain. So things can happen automatically, but even here, the brain can pull the puppet strings to make you walk faster, stutter step, or speed or slow the heart.
Despite these facts, there’s a new concept out there that the brain may also be a servant to what’s happening in the body. For example, we know that depression can be caused by an imbalance of bacteria in the gut. Prior to this discovery, the brain was thought to be the only seat of the roots of depression.
Good Decisions in Real Fight or Flight and Bad Ones in Chronic Arousal
Researchers at Mount Sinai looked at how tachycardia impacted performance and decision-making. The researchers tested the ability of rhesus monkeys to decide between receiving two rewards: either a healthy amount of tasty juice or a little. As expected, the monkeys consistently chose to have more juice, and on average they made this decision faster when their hearts were beating faster, supporting the idea that when the monkeys were in an arousal state, they made better decisions.
On the flip side, when the researchers surgically damaged the amygdala, the brain’s emotional control center, heart rate went up chronically and consistently by 15 beats, indicating that the monkeys were in a chronic fight or flight mode. In this situation, the faster the animal’s heart rate, the worse decisions they made. More interestingly, a faster heart rate was associated with fewer neurons making decisions. Brain scans also showed that the neural signals for decision-making were being high-jacked by the chronic fight or flight reflex. Meaning the body’s ability to make good decisions was impaired.
How Does This Impact Patients in Chronic Fight or Flight?
As discussed above, specific patient injuries can put them into this chronic fight or flight mode. In addition, just having severe chronic pain can do the same thing. Some insight can be gained here by studies of the brains of people in chronic pain.
One of the luminaries in this field of how the brain is changed by chronic pain is a researcher named Vania Apkarian at Northwestern University. I’ve blogged about him before as his research has consistently shown structural changes in the brains of chronic pain patients. For example, he found that the right amygdala was smaller in patients with chronic back pain. Also that patients in chronic pain have a shrunken amygdala compared to controls without pain, just like our monkeys who had their amygdala damaged for this experiment (3).
What is the amygdala? This is the primitive brain center for processing fearful or threatening stimuli. Basically, your fight or flight filter. It also helps to regulate emotions and encode memories.
I’ve often observed that patients in chronic pain have impaired decision-making. Could that be driven by this same mechanism? Their atrophied amygdala, damaged by years of chronic pain, is not able to adequately determine what’s really a threat versus just normal life, leaving them in a chronic fight for flight state? If so, that could cause fewer neurons to be involved in making decisions.
The upshot? Making good or bad decisions is a key part of adulthood. However, could chronic pain destroy the brain circuitry involved in decision-making? Only time and additional research will tell, but this study fits with what I see every day in the clinic.
(1) Atsushi Fujimoto, Elisabeth A. Murray, Peter H. Rudebeck. Interaction between decision-making and interoceptive representations of bodily arousal in frontal cortex. Proceedings of the National Academy of Sciences, 2021; 118 (35): e2014781118 DOI: 10.1073/pnas.2014781118
(2) Abdallah CG, Geha P. Chronic Pain and Chronic Stress: Two Sides of the Same Coin? Chronic Stress (Thousand Oaks). 2017 Feb;1:2470547017704763. doi: 10.1177/2470547017704763. Epub 2017 Jun 8. PMID: 28795169; PMCID: PMC5546756.
(3) Vachon-Presseau E, Tétreault P, Petre B, Huang L, Berger SE, Torbey S, Baria AT, Mansour AR, Hashmi JA, Griffith JW, Comasco E, Schnitzer TJ, Baliki MN, Apkarian AV. Corticolimbic anatomical characteristics predetermine risk for chronic pain. Brain. 2016 Jul;139(Pt 7):1958-70. doi: 10.1093/brain/aww100. Epub 2016 May 5. PMID: 27190016; PMCID: PMC4939699.
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