Applying to a new job, starting a business or relocating to a new country are all examples of stressful situations.
Stress has become ingrained in our daily lives and it has come to a point where it would be unreasonable for us to expect not to have to deal with it.
Let us take a minute to understand what stress actually is.
Stress is more than a feeling. It is a biological response that our body produces because of stress factors or stressors. Anyone preparing for a test, or an important meeting with higher management, having an argument with someone or trying to win a sports match knows what stress is.
When we are stressed, our body releases the stress hormone (cortisol) which gives us the energy to deal with the situation. When the event is over the level of cortisol in our body falls back to normal.
Take an example of a sports match. We naturally play to win and while the match is on, we automatically get stressed. Our cortisol levels go up, keeping us alert and active.
In this case, stress is beneficial. It was a reaction to a temporary event that gave us the energy to control and modify our response based on the situation we found ourselves in.
But when the feeling of being stressed recurs and becomes constant, it is harmful and can have a negative impact on our health.
Chronic stress leads to mood swings, a feeling of irritability and causes us to lose focus. If not treated and managed early on, it can lead to more severe physical complications like gastrointestinal issues, hypertension and heart disease.
The Biology behind Stress
When we encounter a stressful situation, the hypothalamus, located at the base of the brain begins the stress response by sending a message to the pituitary gland. The pituitary gland in turn sends a message to the adrenal glands located on the top of the kidneys. The adrenal glands release the stress hormone, cortisol.
With the help of cortisol, the liver produces glucose and releases it into the bloodstream. The increase in blood sugar level gives us the energy for the fight or flight response. Once the situation in under control, blood sugar levels return to normal.
The series of interactions between the hypothalamus, pituitary gland and the adrenal glands is called the Hypothalamus Pituitary Adrenal axis or the HPA axis.
Although normal levels of cortisol are healthy, increasing levels can wreak havoc with our brain.
Here are a few ways in which stress can affect our brain.
Chronic stress weakens the hippocampus
Rising cortisol levels lead to an increase in the activity level and number of neurons in the amygdala; the part of the brain that controls our emotions. The amygdala is a collection of cells at the base of the brain. At the same time, the electrical signals in the hippocampus decrease. The hippocampus is embedded deep in the temporal lobe and controls our memory, learning and stress controlling ability. It is involved in the regulation of our stress response and exerts negative feedback on the HPA axis, thereby controlling the release of cortisol. But as the electrical signals in the hippocampus decrease, it weakens and reduces our ability to control stress.
High levels of cortisol can cause our brain to shrink in size
High levels of cortisol cause a breakdown of the synaptic connections between neurons and also shrinks the size of the prefrontal cortex. The prefrontal cortex is responsible for cognitive behavior, personality, decision-making and social interaction.
In a study conducted on 103 healthy participants at Yale University, researchers found that those who had experienced traumatic stress and adverse life events, even very recent ones, showed lower gray matter in the prefrontal cortex.
Cortisol makes the brain more receptive to stress
While stress shrinks the size of the prefrontal cortex, it can increase the size of the amygdala which can make the brain more receptive to stress.
Stress kills brain cells and decreases memory and learning ability
High cortisol levels kill newly created neurons in the hippocampus which ultimately decreases our memory and learning ability and can lead to more severe mental illnesses like Alzheimer’s disease.
In a lab experiment conducted on rats, researchers found that a single stressful event could kill new neurons created in the hippocampus.
The researchers placed young rats in a cage with two older rats for around twenty minutes. The young rats were then subjected to aggressive behavior by the older rats. Examination of the young rats found that they had cortisol levels up to six times higher than those of rats who had not experienced a stressful situation. Further examination showed that while the rats subjected to stress had generated the same number of new neurons as those generated by the rats not under stress, there was a distinct reduction in neurons a week later.
High stress causes loss of memory and spatial orientation
The hippocampus has always been associated with storing long term memory and is thought to be responsible for our spatial processing and navigational ability.
The hippocampus is composed of several sub-regions, one of which is the dentate gyrus. The dentate gyrus is composed of densely packed neurons and houses neural stem cells that mature into neurons throughout our adult lives.
Stress causes the hippocampus to lose its ability to produce new neurons in the dentate gyrus thereby weakening our memory and spatial orientation.
Spatial orientation is our innate sense of direction that helps us navigate our environment and get from one point to another. It helps us read maps, find our way to new places by following directions and generally helps us orient ourselves in unfamiliar environments. Without spatial orientation we would be lost and would not know how to get to where we want to go.
Chronic stress diminishes the ability of the hippocampus to generate new neurons, which negatively affects our spatial orientation.
Chronic Stress causes mental illness
Researchers at the University of California, Berkeley have shown that chronic stress causes long term changes in the brain which is why people with chronic stress are prone to mental illnesses like anxiety and mood disorders later in life.
People with stress-related illnesses like PTSD have more white matter than gray matter in their brain. Gray matter mostly consists of neurons and support cells called glia while white matter is composed of axons. Axons create a network of fibers that interconnect neurons. Myelin, a white fatty sheet surrounds the axons and speeds the flow of electrical signals from cell to cell.
A series of studies published in the journal ‘Molecular Psychiatry’ found that chronic stress generates more myelin producing cells and fewer neurons. This results in an excess of myelin or white matter in several areas of the brain which upsets timing and communication within the brain.
Chronic Stress causes Alzheimer’s disease
There are two key toxic proteins responsible for causing Alzheimer’s disease.
The first is beta-amyloid which forms plaques in the brain. Animal models subjected to stress have shown an increase in levels of beta-amyloid.
Tau is the second toxic protein responsible for Alzheimer’s. It forms tangles and is the primary trigger for the death of neurons in people suffering from Alzheimer’s disease.
Studies have shown evidence of hyper-phosphorylation of tau in animal models subjected to stress.
Stress affects brain connectivity
Researchers have also found differences in brain connectivity in people suffering from PTSD. There was stronger connectivity between the hippocampus and amygdala while the connectivity between the hippocampus and prefrontal cortex was weakened. This meant that fear responses in people with PTSD would be quicker while their ability to control fear or to inhibit their response to fear would be lessened.
People suffering from PTSD always have their fear response mechanism activated and are always in fight or flight mode which makes it logical that the connectivity between their amygdala and hippocampus becomes stronger over time.
How to reclaim brain health
Although the effect that stress can have on the brain, looks scary, we needn’t be afraid. Many of the changes that occur in our brain pathways as a result of high cortisol levels, can be reversed.
Positive changes in lifestyle have a direct impact in reducing stress levels and improving brain health
- Exercise regularly for 30 mins a day, four to five days a week
- Get quality sleep of 6 to 8 hours
- Eat a healthy, well balanced diet
- Limit alcohol intake
- Practice Yoga and Meditation