Published on: April 29, 2017
by Anu Kumar for UT Daily Beacon:
While stress is commonly viewed negatively, there is a silver lining. Two classes of stress exist – acute and chronic – and the difference between improving learning/memory performance and implementing your own cognitive decline.
Acute stress, which is defined by short periods of stressful stimuli exposure, is beneficial for you. The hormones that induce “stress” in the brain are active during the moment of the stimuli, but not stay active in the cortex once the stimuli have passed. Chronic stress, which is defined by the prolongation of cortisol-related hormones in the brain, can promote long-term disadvantages, such as changing the ratio of white matter to gray matter in the brain, developing anxiety or PTSD-like symptoms and killing your brain cells.
According to “New Evidence That Chronic Stress Predisposes Brain to Mental Illness,” chronic stress can affect the amount of stem cells in the brain that differentiate into specific types of cells, like neurons, commonly referred to as “brain cells,” or astrocytes, which help regulate neurons. Daniela Kaufer, an associate professor of integrative biology at UC Berkley, has found that part of the reason people experience less-than-ideal cognitive abilities while under chronic stress is because of this abnormal differentiation. She found that after studying neural cells in adult rats, that there was an increase in oligodendrocytes in the rats that were put under chronic stress conditions for prolonged periods of time.
Instead of stem cells differentiating into their “regular” cells, chronic stress prompts them to differentiate into cells called oligodendrocytes. Oligodendrocytes are responsible for producing the insulation, or myelin, around the axons in our nerve cells so that electrical signals can travel quickly and efficiently for our cognitive processes to work properly.
Myelin is classified as white matter; recall that white matter is matter in the brain solely responsible for transferred signals to other parts of the brain. White matter hands the signals off to gray matter, which is responsible for “giving” and “taking” electrical signals.
Therefore, more chronic stress equals more myelin, and less new brain cells being produced. Sometimes, specific connections have higher white matter concentrations, such as the connection between the hippocampus, the main memory hub, and the amygdala, the structure that controls primal responses such as fear. According to the University of Maryland Medical Center’s In-Depth Patient Report of Stress, “Stressful events activate the hypothalamic pituitary-adrenal system, which releases catecholamines .. these chemicals activate the amygdala and suppress concentration, short-term memory, rational thought, and inhibition.” Many scientists believe that this is an adaptation that our ancestors acquired through an evolutionary period.
Christopher Bergland, author of “Chronic Stress Can Damage Brain Structures and Connectivity: Chronic stress and high levels of cortisol create long-lasting brain changes,” postulates that this is related to the fight-or-flight mechanism. While this connection may have worked for our ancestors, whose prime motivation was survival and procreation, it doesn’t work that well for us in modern times. “In a modern world,” Bergland notes, “chronic stress can hijack a fight-or-flight system and backfire in a daily life in which you are in no physical danger.”
This gives us a closer look to how many anxiety disorders are expressed in people, and can explain why some trauma survivors can have frequent flashbacks that closely resemble symptoms of PTSD.
Constant exposure to chronic stress can leave you susceptible to nerve damage because of the changes in your brain chemistry. The blood-brain-barrier, which acts as a filter to keep certain chemicals out of your brain, can be damaged as noted by the British Medical Journal’s article, “Stress may disturb the blood-brain barrier.” That itself is a different facet of risk that I encourage you to look at separately.
Despite all these terrible things that can happen, there is a bright side! Depending on the degree of changes that chronic stress has affected on a brain, the wonders of neuroplasticity can help reverse some, if not all, of the negative changes.
In 2012, Alex Schlegal of Dartmouth College published a study regarding the way a student’s brain can change when they learn a new language. 27 students were enrolled in a 9-month Chinese course, and their white matter makeup was recorded before and after the study using Diffusion Tensor Imaging (or DTI). Instead of a typical MRI scan, DTI measures the diffusion of water in the axons. This allows us to see how frequently regions of the brain are communicating before and after the experiment. Less communication in an area meant that more white matter, or myelin sheaths, were present. The results found that communication in the brain improved for each of the students, even though the degree of improvement was varied.
As previously stated, acute stress is much more beneficial for the brain rather than chronic stress. Kaufer and Elizabeth Kirby, a post-doc in Kaufer’s lab, discovered a chemical sequence that occurs when mice are under acute stress versus chronic stress. Stress hormones, such as corticosterone, stimulates the astrocytes in the brain, which then releases the protein FGF2, fibroblast growth factor 2. According to Sanders’ article, “FGF2 deficiency is … linked to depression in humans.” However, even Kaufer notes that acute stress that is extremely intense can also promote negative results in terms of cognitive performance.
The relationship between the brain’s health and stress is a very finicky one, and there isn’t any recent research that points to the universal preferred amount of stress because everyone’s brain is different. However, knowing that continuously putting yourself in positions of high stress can be damaging is half the battle. Sometimes we are blind to the amount of unnecessary stress we put ourselves through, in which case, talking to a counselor or taking a self-assessment from a trusted source can put you on the right track to a more balanced and happy brain.
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