How Stress Harms Cognition
Cognition is just a fancy word for a thought. It’s the way you think about what’s happening.
~David D. Burns, MD[i]
Long-term exposure to large doses of cortisol will kill you … but slowly.
~ Robert H. Lustig[ii]
Any level of stress inhibits performance.
~Judson Brewer, MD, PhD[iii]
The Summary
Stress is toxic to the brain. The rat-fumbling researcher, Hans Seyle, noticed that the discomfort his lab rats suffered made them sick. He used the term stress to describe the general unpleasantness his rats experienced when he routinely dropped, chased, and recaptured them during his experiments. The culture of his lab was making his rats sick.
Unrelenting stress is part of our culture. According to Jon Kabat-Zinn, overwhelm is the experience “that our lives are somehow unfolding faster than the human nervous system and psyche are able to manage well.”[iv] The fight-or-flight stress response is initiated by the nervous system. Designed to promote the short-term action necessary to flee from or fight predators, our stress system is now routinely activated by modern stressors in our environment. Long-term activation of our stress response makes us physically and emotionally sick, and it damages our brain.
The Science
Wisdom of the Body
We use both the thinking and emotional brains to process emotion. An emotion is an automatic and unconscious response to an emotional stimulus that results in physical and cognitive changes. Examples of the body responding spontaneously to an emotion include blushing, sweaty palms, and increased heart rate and blood pressure. The six primary emotions are: sadness, fear, anger, disgust, surprise, and joy. Emotions are experienced as feelings, which are the conscious perceptions of the involuntary responses of the body to emotion.[v]
Information travels through the brain along two parallel processing routes. First, stimuli, also known as memory traces, enter the thinking brain via the senses, then they move to the emotional brain. The quick and dirty route starts in the emotional brain’s panic button, the amygdala. The amygdala is alert to threat and opportunity, and it launches the body’s fight-or-flight system in response to danger. On the slower route, information is processed by the hippocampus in the emotional brain, and in the absence of threat, the fight-or-flight stress response is overruled.[vi]
Walter B. Cannon was a physician, professor of physiology at Harvard, and a stress and trauma researcher who coined the term homeostasis in 1926. His research on how emotional states impact bodily functions also led him to coin the phrases fight-or-flight and rest-and-digest to describe the two parts of the autonomic nervous system. He theorized that these systems helped the body maintain the stability that he called homeostasis. Cannon characterized this homeostatic operation, working to balance the right amount of alertness with relaxation, and anxiety with calm, as the wisdom of the body.[vii]
The brain works with the body to maintain homeostasis via the autonomic nervous system. Homeostasis can be compared to a heating, ventilation, and air conditioning (HVAC) system. We use our HVAC system to maintain a comfortable temperature in our home. The autonomic nervous system has a heating half, the sympathetic nervous system, and a cooling half, the parasympathetic nervous system. These systems were described by Cannon as the fight-or-flight (sympathetic nervous) system and the rest-and-digest (parasympathetic nervous) system. The fight-or-flight arousal system is the body’s accelerator and the rest-and-digest calming system is its brake.[viii]
The fight-or-flight system evolved to produce rapid response when escape from predators was a priority. It is ignited by the threat sensor amygdala, which directs the thalamus to focus attention and the hypothalamus to inform the pituitary, which instructs the adrenal glands to release the stress hormones adrenalin, also known as epinephrine, and glucocorticoids, mainly cortisol. This is the HPA Axis: hypothalamus to pituitary to adrenal glands. The amygdala signals the HPA Axis to respond to threat and launch the cascade of stress hormones. Stress hormones increase heart rate, raise blood pressure, and elevate blood sugar to provide an energy boost intended to help the body deal with the threat. At the same time, systems designed to support long-term health, such as digestion and the immune system, are suppressed.[ix]
Fight-or-flight activation is meant to help solve short-term problems, like the evasive action necessary to escape harm. The wisdom of the body uses the rest-and-digest system to return to homeostasis after the threat has been neutralized. However, there are two kinds of stress: acute stress, which is short-lived and for which the fight-or-flight system evolved; and chronic stress, which is long-term and caused by serious life challenges such as job loss, financial difficulties, intimate relationship struggles, and health issues.
Acute Stress
The short-term stress response was devised to help us with performance and survival. It improves vigilance and directs blood flow to fuel the brain, heart, and muscles. It was designed to be experienced in small doses.
The fight-or-flight acute stress response can focus a person and enhance performance in a difficult or a demanding situation. It also empowers the body to participate in a weekend 5k run. Once the important task is resolved, the body and brain should be able to return to homeostasis via the rest-and-digest system.
The problem with society today is that acute stressors have been greatly reduced, but chronic psychological stressors have increased significantly. And chronic stress can damage your brain, and ultimately kill you.[x]
Chronic Stress
When stress persists for days or weeks, fight-or-flight activation can cause stress-related mental disorders such as irritability, anxiety, panic attacks, or depression. The physical effects of chronic stress can include breathlessness, dizziness, heart palpitations, chest pain, sweating, chills, abdominal discomfort, muscle tension, and elevated blood pressure. These symptoms indicate an unrestrained fight-or-flight response.
Chronic stress promotes long-term elevation of stress hormones, causing increased risk for the following serious health problems: a compromised immune system; increased appetite and body fat; decreased muscle mass and bone density; diminished libido; and increased anxiety and depression. It can lead to metabolic syndrome, a group of symptoms including increased blood pressure, blood sugar, cholesterol, and triglyceride levels, and body fat around the waist, which together with metabolic syndrome raise the risk of diabetes, stroke, and heart disease. Chronic stress has serious consequences for the brain as well.[xi]
How Chronic Stress Causes Brain Damage in the Emotional Brain
The emotional brain structures reside deep in the brain, and they are surrounded by the thinking brain, which is the wrinkled top layer that resembles a walnut. Key structures in the emotional brain are the panic button amygdala and the memory-processing hippocampus.
Overactivation of the stress system can have grave consequences for the health of the brain. Stressed out people can spend months or years in fight-or-flight overdrive, many believing their work is enhanced by the adrenaline-cortisol rush. The performance upgrade stimulated by the short-term activation of the fight-or-flight system is only effective if the rest-and-digest system regularly returns the brain and body to equilibrium. Under chronic stress, the brain never gets a chance to recover, and it is susceptible to damage caused by extended exposure to stress hormones.
Sensing threat, the amygdala sounds the alarm by stimulating the release of stress hormones to the body and brain via the HPA Axis. During chronic stress, continuous fight-or-flight activation causes iterative damage to the brain. Stress hormones arouse the amygdala, which responds by instigating the production of additional glucocorticoids. The memory-processing hippocampus is highly susceptible to stress because it has abundant glucocorticoid receptors. Glucocorticoids damage and kill neurons in the hippocampus and weaken synaptic connections between brain cells.
The hippocampus, normally responsible for calming the amygdala, is suppressed. Under chronic stress, the amygdala is over sensitized, and the hippocampus is compromised. The memory-processing hippocampus is the brain structure most vulnerable to cell death, causing hippocampal shrinkage, memory loss, and depression.[xii]
Because the job of the panic button amygdala is to react to trouble, the brain is vulnerable to negativity bias, where the mind can trigger a stress response by simply imaging a threatening situation. Fear of a threat can launch the stress response, and it can keep it going. This can happen when a person worries about a short-term task, or has anxiety about a long-term goal.
Executive control within the thinking brain is diminished, so it becomes difficult for the anxious person to calm the apprehension of a potential public blunder or career failure when the thinking brain is exposed to chronic stress.
To recap, chronic stress can be caused by real physical threats, or by psychological threats, such as worrying about the pressures of work or relationships. This is an automated process. People cannot control the brain’s involuntary response to chronic stress. The emotional brain is inundated by a constant stream of stress hormones. The memory-processing hippocampus is susceptible to brain cell damage and death, and this can result in memory problems and depression.
Stress-infused cultures are likely to cause cognitive dysfunction due to the harm stress hormones cause in the emotional brain.
How Chronic Stress Causes Brain Damage in the Thinking Brain
Fight-or-flight is the body’s protective system designed to deal with acute stress which could be physical, adversarial, medical, or psychological. When cortisol is released, we get a burst of blood glucose to prevent fainting, increased blood pressure to prevent shock, and suppressed immune function to prevent inflammation. Vigilance and memory are heightened, and blood flow increases to support the action of the muscles, heart, and brain. The fight-or-flight system is designed for brief engagement, in small doses, to successfully handle short-term challenges.
In the thinking brain, stress causes the amygdala and HPA Axis to release cortisol and dopamine into the prefrontal cortex (PFC). This impairs rational decision-making, causes impulsivity, and harms the ability to distinguish between immediate or delayed gratification. Dopamine is the transmitter designed to inspire repeat behavior. Dopamine receptors in the thinking brain are fewer than in the emotional brain and they down-regulate (shrink in number) with overexposure, attempting to limit the impact.
Stress and cortisol decrease the cognitive control of the thinking brain PFC, making comfort food and drugs of abuse more difficult to resist. Self-medication becomes a health risk for the stressed-out individual, even if she is trying to break bad habits. The PFC has significant difficulty managing the drive for short-term relief that stress instigates, which can also lead to substance misuse and addiction.
Chronic stress can also kill brain cells in the front part of the frontal lobe, the prefrontal cortex (PFC), known as thinning of the PFC. A compromised PFC is a predictor of risk of relapse to self-medicating with food or drugs. When stress hormones damage or kill thinking brain PFC neurons, the result is poorer decision-making capacity and the risk of turning to bad habits to provide a respite from stress.[xiii]
Cognitive Capacity, Learning, and Memory Under Chronic Stress
The memory processing hippocampus is highly vulnerable to injury from overexposure to stress hormones. It has plentiful glucocorticoid receptors and stress hormones can damage or destroy the neurons in the hippocampus, along with weakening the synaptic connections between neurons. As with other body functions devoted to long-term well-being that are inhibited during chronic stress, such as digestion and immune response, the birth of new brain cells in the hippocampus is also suppressed.
A number of other conditions can harm the hippocampus, including radiation and starvation. “One of the serial killers that attacks the neurons in the hippocampus is cortisol. The longer your cortisol stays elevated, the smaller and more vulnerable your hippocampus gets, which puts you at risk for depression. This is likely why chronic stress is associated with memory loss.”[xiv]
One study revealed that adults in midlife with increased levels of stress hormones had reduced brain structure and cognitive function. Data from 2,018 Framingham Heart Study participants, of an average age of 48, showed that participants with an elevated cortisol level performed worse on memory and other cognitive tasks than participants with average cortisol levels. The participants with higher cortisol also had smaller brain volumes.[xv]
It should come as no surprise that a compromised hippocampus is not as functional as a healthy one. The impact of stress on cognition includes deterioration in concentration, memory, problem-solving, math performance, and language processing. Motivation is dampened, curiosity is diminished, and creativity is inhibited. Brain scans show that the hippocampi shrink in people who experience major depression and post-traumatic stress disorder (PTSD). This shrinkage is likely due to hippocampus neurodegeneration caused by overexposure to stress hormones.[xvi]
Empowering Recovery
Short term stress, chronic stress, and trauma all activate the fight-or-flight stress response system. Chronic stress and trauma can harm both the emotional and thinking brains when the stress response system is overactivated or incessantly triggered.
Many people spend their lives in fight-or-flight overdrive. This predicament may be fueled by caffeine, comfort food, alcohol, and other substances. Some highly intelligent s are individuals are likely to be more susceptible to stress and trauma, and some are likely more vulnerable to toxically stressful environments. Neuroscientists have proven that cognitive performance is diminished during extended fight-or-flight response, but thanks to neuroplasticity, the brain can be healed. It is possible to become an “amygdala whisperer” and recover cognitive function.[xvii]
A healthy rest-and-digest system can blunt the stress response and improve the capacity to return to homeostasis. We can empower our rest-and-digest system as part of a plan to reduce the impacts of stress. While the fight-or-flight system stimulates arousal, defense, and escape, the rest-and-digest system supports nourishment, procreation, and restored balance after a stress response. The rest-and-digest system slows the heart rate, lowers blood pressure, promotes digestion and nutrient absorption, and curbs the release of stress hormones. It conserves energy, promotes relaxation, and produces feelings of contentment.
The rest-and-digestsystem’s ability to reduce stress hormone levels can help heal both the emotionaland thinking brains. We can cultivate the neurobiology of calm and foster resilience in the face of stress with a series of restorative practices such as mindfulness, meditation, gratitude, time spent in nature, pet therapy, and creative play.[xviii]
[i] David D. Burns, MD, Feeling Great: The Revolutionary New Treatment for Depression and Anxiety, at 15 (2020).
[ii] Robert H. Lustig, The Hacking of the American Mind: The Science Behind the Corporate Takeover of our Bodies and Brains, at 61 (2017)
[iii] Judson Brewer, Unwinding Anxiety: New Science Shows How to Break the Cycles of Worry and Fear to Heal your Mind, at 82 (2021).
[iv] Katie B. Smith, Medium, quoting John Kabat-Zinn, Apr 9, 2022, Stress Got the Best of You?. Stress includes any invasive influence… | by Katie B. Smith, Executive & Career Coach, PCC | Apr, 2022 | Medium.
[v] Ralph Adolphs & David J. Anderson, The Neuroscience of Emotion: A New Synthesis, at 6 (2018).
[vi] Rita Carter, Mapping the Mind, at 83 (2010).
[vii] Gayatri Devi, A Calm Brain: How to Relax into a Stress-Free, High-Powered Life, at 37 (2013); Robert M. Sapolsky, Why Zebras Don’t Get Ulcers, at 12-13 (2004).
[viii] Melanie Greenberg, Ph. D., The Stress-Proof Brain: Master your Emotional Response to Stress using Mindfulness and Neuroplasticity 20 (2017).
[ix] John Medina, Brain Rules: 12 Principles for Surviving and Thriving at Work, Home, and School, at 62-67 (2009).
[x] Lustig, supra note 2, at 60-61.
[xi] Greenberg, supra note 8, at 23-26; Medina, supra note 9, at 63-67; Lustig, supra note 2, at 61-66; Carter, The Human Brain Book, at 232 (2019); Shawn Talbott, The Cortisol Connection: Why Stress Makes you Fat and Ruins your Health-and What you Can Do About It, at 30-33 (2007).
[xii] Medina, supra note 9, at 65-67; Greenberg, supra note 8, at 2-24.
[xiii] Rick Hanson, Buddha’s Brain: The Practical Neuroscience of Happiness, Love, and Wisdom, at 52-60 (2005); Lustig, supra note 2, at 64-66.
[xiv] Lustig, supra note 2, at 63.
[xv] Muzaffer Kaser, Barbara Jacquelyn Sahakian and Christelle Langley, How Chronic Stress Changes the Brain, and What you can do to Reverse the Damage, Neuroscience News, Mar. 14, 2020, https://neurosciencenews.com/chronic-stress-reversal-15918/.
[xvi] Medina, supra note 9, at 178; Sapolsky, supra 7, at 221.
[xvii] Hanson, supra note 13, at 52-60.
[xviii] Taylor Clark, Nerve: Poise Under Pressure, Serenity Under Stress, and the Brave New Science of Fear and Cool 81 (2011).