Can you recall feeling restless, having trouble sleeping, being irritated and moody? There was probably something exciting (good or bad) going on in your life that you were stressed about. Stress is literally a reaction of your body to a challenge – any challenge or demand at all. In daily life, people use the word stress to state that they feel overwhelmed and/or not in control. It is usually related to an unhealthy and undesirable state of mind. Whether this is true depends on the duration of the stress response.
Evolutionarily speaking, experiencing stress in the short-term (acute stress) was used to keep us alive. It causes a quick activation of the ‘flight-or-fight’ response which is very helpful in dangerous situations or when you need to accomplish something challenging. Good examples of this are when you need to lift a car off your child or when you need to fight a bear. In both cases, many people experience what they feel to be superhuman strength. In reality, they are utilizing stress through the flight or flight reaction. But when you experience stress for too long it becomes chronic (long-term and reoccurring), and that causes numerous negative effects for you brain and body.
The journey of the stress hormones
Some people refer to stress as an emotion (for example ‘I am feeling stressed’) that occurs when they are under a time pressure. For example: when they do not have the time to perform a task within the desired or given period of time. The stress itself is merely a physical phenomenon in your body that does not depend on an objective event such as time pressure. But the cause of that phenomenon is indeed related to the feeling of being overwhelmed. In general, the feeling that one person is not in control over the situation leads to a neurological stress response in the body (Lupien et al., 2007). This feeling of not being in control can be triggered by a number of causes such as: being in or witnessing an accident, being exposed to extreme heat or cold, confronting a dangerous animal or giving a public speech.
It begins with Hypothalamus Pituitary Adrenal Axis (HPA Axis). This is the process of stress hormones being made (see the picture below). When a situation is interpreted as being stressful, the hormones CRH and ACTH are released from the Hypothalamus and Pituitary gland respectively. They travel to your adrenal glands and eventually cause the production of the stress hormones (Lupien et al., 2007).
The three stress hormones that are released are: Cortisol, Adrenaline, and Noradrenaline. These hormones travel through your bloodstream and come in contact with each cell in your body. Adrenaline and Noradrenaline prepare the body for a flight-or-fight response, which you can feel by an increase in heart rate and blood pressure. It disappears from your body when the situation is over. Cortisol flows through your body all day and causes a variety of effects. To summarize: During a stressful situation, your body increases the available energy and prepares for changes in your environment like an attack or use of strength/speed (Lupien et al., 2007). The activation of the HPA axis is a basic mechanism in response to change but a continuous activation presents some serious health risks to your body. First of all, because long-term high blood pressure will increase the risk of developing diabetes, hypertension, and diseases. Secondly, the activation of the HPA axis suppresses the immune functions, tissue repair, the growth of new cells and digestive functions. Therefore, long-term exposure to stress can be damaging to your body.
And the journey continues inside your brain…
Did you know that having chronic stress (and therefore having chronic exposure to these stress hormones) also has an impact on the size, structure and functioning of your brain? The brain contains a lot of stem cells that evolve into specific types of cells when they mature. Studies have shown that chronic stress has the ability to flip a switch in these stem cells turning them into a type of cell that is different from their original destination (Lupien et al., 2009). This causes your brain to change in a way that is not according to how your DNA intended.
The overproduction of the stress hormones has three important consequences (Chetty et al., 2014; Davidson & McEwen, 2012).
- It increases the activity in the Amygdala – the fear center of your brain. High levels of cortisol create a hard-wired pathway between the Amygdala and Hippocampus, which creates a brain that is in a constant state of ‘flight-or-fight’. MRI scans show that the Amygdala increases in size in cases of chronic stress.
- It lowers the activity in the Hippocampus. The Hippocampus is the center for learning, memorizing, handling emotions and stress control since it regulates the HPA axis activity. Stress lowers the development of new brain cells and MRI scans also show that some areas actually shrink.
- It decreases the activity in the Prefrontal Cortex. This is the center of decision-making, concentration, judgment and social interaction. Some areas in the Prefrontal Cortex also shrink a little under continuous high levels of stress.
Grey and white are all that matter
Maybe the shrinking and growing of areas in the brain sound a bit odd. Although it can be argued that the brain is like a muscle, your head won’t increase or decrease in size depending on the amount of exercise. Within the brain, it is all about activity. Let’s dive a little deeper into how this works.
When people refer to the brain, they often talk about the ‘grey matter’. This grey matter consists of densely packed nerve cell bodies (neurons) that do the thinking, computing, and decision-making. But all these cell bodies are connected with each other through axons (or network cables) that cover almost half of the brain volume. This communication network of axons has a distinctive light color and is therefore called ‘white matter’. A consequence of continual exposure to stress hormones results in a decrease in the number of cell bodies. Some of the existing ones die or show almost no activity and fewer new ones are made. The overall activity of the grey matters lowers and the same goes for the white matter. The axons die or become inactive, and fewer new axons are being developed. The decrease in cell bodies and axons within the Prefrontal Cortex and Hippocampus will result in problems with learning, memorizing, stress control and decision-making amongst other things.
How about the reverse button?
Many studies claim that the structure of the brain is largely determined during childhood. This means that young people who have been exposed to high levels of stress (for example because of too many radical changes, dangerous situations or a lack of nurturing) may develop life-long anxiety issues, mood disorders and/or learning difficulties (Hanson et al., 2015). Although most researchers agree with this statement, there is a growing amount of research about the activity in the grey and white matter that shows that the adult brain is actually able to change for the better if you work on reducing stress (Schlegel et al., 2012; Davidson & McEwen, 2012).
Getting your brain back on track
The brain is a dynamic organ that evolves during your lifetime. Therefore, changes in the Amygdala, Hippocampus, and Prefrontal Cortex are reversible although it gets more difficult to do so as you age. Although stress itself is a physical phenomenon with neurological implications, it all starts with the individual’s perception of feeling out of control. This is the key to reversing its effects. It may sound simple but a lot of research has shown that meditation is a great way to reduce the production of stress hormones. Mindfulness, cognitive training, and physical exercise are proven to be the best ways to get back in control of your life.
You might also be interested in the following individual reading comprehension articles:
Health:
• The Common Cold
• The Flu
• Exercise and its Importance for Health
• Stem Cell Therapy: The Future of Medicine?
• Concussions
• Poliomyelitis – Polio
• Smallpox
• The Measles
• Genetics and Gene Therapy
• Heart Diseases
• Cancer
• The Effects of Caffeine
• Down syndrome
• HIV/AIDS – – Informing the Public and Dispelling the Misconceptions
Energy:
• Fossil Fuels
• Nuclear Energy: Fission and Fusion
Chemistry:
• The Chemistry of Explosions
• Plastics: A Marvel Of Innovation
• The Chemistry of Paint
Physics:
• Magnets and Electromagnets
• The Limitations of Space Travel
Natural Disasters:
• Volcanoes: The Benefits and Devastation
• Earthquakes
• Tsunamis
Ecology:
• Invasive Species
• Pesticides
• The Importance of Bees
• Coral Reef Ecosystems and their Future
References
Chetty, S., Friedman, A.R., Taravosh-Lahn, K., Kirby, E.D., et al. (2014). Stress and
glucocorticoids promote oligodendrogenesis in the adult hippocampus. Molecular
Psychiatry, 19, p. 1275-1283
Davidson, R.J. & McEwen, B.S. (2012). Social influences on neuroplasticity: stress and
interventions to promote well-being. Nature Neuroscience, 15, p.689-695.
Hanson, J.L., Albert, D., Iselin, A., Carré, J.M., Dodge, K.A. & Hariri, A.R. (2015). Cumulative
stress in childhood is associated with blunted reward-related brain activity in
adulthood. Social Cognitive Affective Neuroscience, 5.
Lupien, S.J., Maheu, F., Tu, M., Fiocco, A. & Schramek, T.E. (2007). The effects of stress
hormones on human cognition: Implications for the field of brain and cognition. Brain
and Cognition, 65,p. 209-237
Lupien, S.J., McEwen, B.S., Gunnar, M.R. & Heim, C. (2009). Effects of stress throughout the
the lifespan of the brain, behaviour, and cognition. Nature Reviews Neuroscience, 10,
p. 434-445.
Schlegel, A. A., Rudelson, J.J. & Tse, P.U. (2012). White matter structure changes as adults
learn a second language. Journal of Cognitive Neuroscience, 24(8), p. 1664-1670.