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How stress affects the brain

How stress affects the brain

What is stress ?

And yet, its popular use is quite recent: the word was introduced into medicine in 1936 by Doctor Hans Selye, an endocrinologist at the Institute of Experimental Medicine and Surgery (University of Montreal Canada). Its definition is linked to physiology and psychology: “  Aggression of the organism by a physical, psychic, emotional agent leading to an imbalance which must be compensated by a work of adaptation; an agent who assaults; nervous tension, the stress of the body in the face of a shock (sudden event, trauma, strong sensation, noise, overwork); state of a person subjected to this tension ”[1].

The word “stress” therefore designates several concepts. It can qualify:

·         the agent causing the reaction ;

·         the reaction itself ;

·         the state resulting from the reaction

Either way, stress is often seen as negative. In health, stress – a reaction allowing adaptation to different external or internal conditions – is nevertheless the body’s protective factor. It participates in the various systems intended to preserve our vital functions and by extension, our vital organs and therefore our brain.

Stress, a protective mechanism

For our body and our safeguard, stress is therefore above all, a set of reactions of our organism to a threatening or new situation: the “stressor” agent, the stimulus. The perceived psychological stress then triggers backup reactions and allowed our ancestors to survive by escaping dangers, adapting to new environments, changes, and evolution.

Today’s stressors are different. In our society, no wild beast to stimulate our reaction, but social situations are more or less felt as stressful agents: a verbal threat, an exam, a competition, financial problems, family, an accident, noise, etc. Threats or stimuli have changed, but our basic reactions remain the same.

How does stress affect our brain?

Faced with stimuli, our body must react and many brain structures help mobilize organic functions to induce behavior conducive to safeguarding. The stimuli mainly reach the brain areas involved in emotions and coordination.

The representations of the stimuli first reach the amygdala, then the hippocampus  and the prefrontal cortex:

  • The amygdala , part of our brain close to the hippocampus, is essential to our ability to feel and perceive emotions . The amygdala is a complex brain structure made up of small regions including the lateral nucleus, the entryway for information, and the central nucleus from which the commands for reactions originate. These cores represent the heart of our alarm system. The amygdala therefore plays a role in activating the reaction . It also plays an important role in the recognition of our emotions.
  • The hippocampus participates in the regulation of mood , the acquisition of knowledge and more generally in the adaptation to the environment .
  • The prefrontal cortex , a brain structure located behind the forehead, is the center of decision-making , the keystone of our composure.

Of course, all of these areas respond to stimuli at the biological level by releasing neurotransmitters and hormones.

Neurotransmitters and hormones involved in stress

The neurotransmitters are chemical compounds released by neurons in the synaptic cleft. They are comparable to a key (the shape must correspond to the lock, that is to say the receptor) and will make it possible to trigger excitatory or inhibitory effects on the receptor neurons.

The neurotransmitter GABA (gamma-aminobutyric acid) regulates anxiety by reducing the activity of the neurons on which it attaches. It is the main inhibitory neurotransmitter in the nervous system. It is also on GABA receptors that modulating drugs such as benzodiazepines, barbiturates, and also a psychoactive substance: alcohol act.

Other neurotransmitters also act on the alarm system  :

  • the serotonin which regulates temperature, sleep, mood, appetite and pain;
  • the glutamate , a stimulant associated with the memory;
  • the noradrenaline active in attention, emotions, dreams, sleep and learning;
  • the acetylcholine , implicated in arousal, attention, anger, aggression, sexuality and thirst. It triggers muscle contraction and stimulates the secretion of hormones;
  • the dopamine , involved in the control of movement and posture, as regulating mood.

Some of these chemical molecules (neurotransmitters) are also considered hormones. The physical manifestations of stress are strongly related to hormonal action. At least five hormones are involved:

  • the norepinephrine precursor of adrenaline , is released by the adrenal glands into the blood stream. It promotes the contraction of blood vessels and therefore helps to increase blood pressure and heart rate;
  • the cortisol , secreted by the adrenal gland regulates blood pressure, heart function and immunity, and provides the brain with sufficient energy to prepare cope with stress;
  • the adrenocorticotropin ( ACTH ) is secreted by the pituitary gland itself active under the influence of a hormone released by the hypothalamus.  the oxytocin , the hormone of the social bond and attachment, control anxiety, is mainly produced by the hypothalamus (she also plays the role of neurotransmitter) and enters the bloodstream to the pituitary gland to be distributed to organs;
  • the vasopressin hormone antidiuretic, increases water permeability and thus reduces the volume of urine, regulates blood pressure as a vasoconstrictor, plays a role in anxiety.

The adaptation reaction to a stressful situation

The role of these neurotransmitters and hormones is to allow the body to release the necessary forces and energies in the face of the perceived threat. This complex biological reaction follows two steps that will allow the body to respond to the stressful situation  :

  1. The shock stage  : emotions stimulated, senses mobilized

Perception of the situation, the mind becomes confused, muscle tone weakens, the level of sugar in the blood plummets, and physical manifestations appear: pallor of the face, feeling of “tight” throat, knotted stomach, sweating, tremors, malaise, etc.

  1. The reaction stage  : the brain reflects and / or the body prepares to flee, to defend itself

The hypothalamus is activated and first mobilizes the so-called “sympathetic” branch which controls the body’s autonomous activities (breathing, heartbeat, smooth muscle contractions) and produces stress hormones via the adrenal glands, then calls on it. hypothalamus-pituitary-adrenal cortex axis to produce cortisol.

The body goes into a “state of alert”, and triggers a real hormonal storm: the adrenaline released promotes the mobilization of both physical and mental forces, with increased heart rate and blood flow, redistribution of fluids to the brain and muscles, muscle tension, activation of the production of cortisol to release glucose from the liver and provide energy for the brain and muscles.

Acute or Chronic Stress – Good Stress and Bad Stress?

The psychological impact of stress depends on the duration of the stress:

  • Acute stress is mobilizing  : attention is focused on the stressor, the senses are on alert, hormones are produced and the situation is more or less quickly managed.
  • Chronic stress is debilitating  : it results from prolonged and repeated exposure to the stressor and therefore an “alert” mode activated continuously. Hormones are continuously secreted without resting the body and therefore can lead to exhaustion of the body.

Prolonged or repeated exposure to the stressor depletes the body’s energy capacity, the blood glucose level is at its lowest, the cells are no longer nourished: the state of exhaustion is reached. The state of exhaustion becomes a fertile ground for the development of diseases. The cells are weakened and the neuro-hormonal system is out of order, blood cholesterol is no longer regulated.

Chronic stress strongly impacts the good health of the organism. Exhaustion leads to heart disease, constantly high blood pressure, increased cholesterol levels, diabetes, stomach ulcers, reduced immune defenses, etc. The state of chronic stress also affects the emotional state, behavioral and cognition: depression, constant aggressiveness, emotional fatigue, nervousness. Psychological disorders can arise and disrupt decision-making: difficulty concentrating (thoughts mobilized on the stressor), memory problems, heightened anxiety, emotionality, restlessness, disturbed sleep.

How to fight stress?

The ability to adapt to a stressful situation is intimately linked to the person, his experience, his memory, his state of health, his perception of the situation. Stress management must therefore be individualized. The common line to counter the harmful effects of stress lies in action. The activity will help to deflect aggression and frustration. The activity can be physical or mental.

Four steps will allow everyone to learn to manage their stress  :

  • Knowing how to listen to your body and psyche to detect the first signs of the harmful effects of stress;
  • Learn to recognize the stressors that surround us (individual perception);
  • Understand our reactions to stressors;
  • Find a “stress channeling” activity corresponding to each stressor.

Scientific studies agree to provide guidance on useful practices in stress management  :

  • Mental relaxation  : meditate, relax, listen to music, paint, write, talk with friends.

Holidays reduce stress-related processes, but the biological impact of meditation is even more significant. Meditation reduces symptoms of depression and stresses more lastingly than a vacation.

Focus on a trivial task (informal mindful mediation) focusing on details such as smell, touch, temperature, etc. the stress level is reduced and the feeling of mental well-being is increased.

Listening to music has a similar effect to meditation and is beneficial against stress.

  • Physical relaxation : physical  activity, walking, running, cycling, swimming, cleaning, gardening.

People who exercise regularly have less stress at work than those who do not participate in physical activity.

Yoga and Tai Chi are practices that combine movements, mastery of the gesture, and concentration.

Deep breathing provides oxygenation and stimulates the parasympathetic system which reduces the heart rate and promotes calm.

Stressors cause a physiological reaction in the body that allows the body and mind to mobilize to initiate safeguarding. This reaction is beneficial in the case where the duration and the repetitiveness remain limited. When the body is exhausted to respond to chronic stress, physical and mental condition can deteriorate very quickly. It is therefore important to know how to listen to your body to anticipate the harmful effects of stress. Understanding the mechanisms to act better, on the mind and on our body, adopting an attitude of mental relaxation and practicing physical relaxation every day are preventive actions to adopt to suffer less from chronic stress.


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