THE STRESS RESPONSE evolved as a survival mechanism and is a set of biological processes which react to a stimuli that is perceived as threatening or frightening. The response triggers the release of a cascade of hormones that produce a number physiological changes in the body and prepares it to fight, flight or freeze. This evolutionary response increased the likelihood of survival in dangerous situations.
It is known that repeated activation of the stress response has serious long term adverse effects. Chronic stress increases blood pressure and causes changes in the brain that can contribute to anxiety, depression and addiction.
How an incoming threat triggers the response
Incoming sensory information is processed by the thalamus and, if perceived to be a threat, passed to the amygdala which is often referred to as the centre of the emotional or primitive brain. The amygdala has influence over two other areas in the primitive brain, the hippocampus and the hypothalamus. The hippocampus plays an important role in the consolidation of information from short-term and long-term memories. It contains a library of behavioural patterns that has built up over time on responses to certain stimuli or events, some of which are inappropriate.
The hippocampus is packed with cortisol receptors and chronic stress can flood the hippocampus with this hormone. Over the long-term this can cause brain cell necrosis (cell death) in this region. The amygdala requests context from the hippocampus about the threat, “have we seen this before or something like it and if so, what did we do?”
The amygdala also sends a distress signal to the hypothalamus which is responsible for chemical regulation within the body and brain. The hypothalamus communicates with the rest of the body though the autonomic nervous system (ANS). The ANS is made up of the sympathetic nervous system, responsible for preparing the body for the fight or flight response and the parasympathetic nervous system whose role is to ensure bodily functions operate normally. The parasympathetic nervous system also promotes rest and digest and decreases arousals to return the body to homeostasis or equilibrium.
The hypothalamus activates the sympathetic nervous system by sending signals to the adrenal glands telling them to produce the hormone adrenaline which is then released into the bloodstream. Adrenaline has a physiological effect on a number of organs in the body when it is detected. Heart rate is increased in an attempt to pump more blood to the muscles in readiness for action. Blood is pumped away from the stomach to other organs and blood pressure is increased.
“The stress response can be activated through negative thinking”
At the same bronchi in the lungs begin to increase in an effort to take in more oxygen which is used in the brain to increase alertness. Other senses become heightened such as hearing and sight, pupils dilate to take in more light. Adrenaline causes fats and sugars to be released which the bloodstream then carries throughout the body.
This initial response happens so quickly that the conscious part of the brain is unable to process this. It does explain however, how people seemingly automatically react to a threat.
The HPA Axis
The hypothalamus continues with the response by invoking the HPA axis or the Hypothalamus-Pituitary-Adrenal axis – a complex feedback systems between these three structures. Corticotrophin Releasing Hormone (CRH) is released by the hypothalamus and received at the receptors of the pituitary gland. When CRH is received it triggers the pituitary gland to release the hormone called adrenocorticotropic hormone (ACTH) which then travels to the adrenal gland and stimulates the release of adrenaline and cortisol.
Cortisol instructs the body to release glucose from its stores of glycogen in the liver and muscles. This provides the energy the body requires to deal with the threat. Cortisol is a more sustained response than adrenaline and used for when threats do not pass quickly.
Once the threat has passed cortisol levels drop and the hypothalamus will stop releasing CRH. The parasympathetic nervous system begins to return the body back into an equilibrium state.
How our thoughts can trigger the stress response
Although the stress response is invoked when there is a real external threat it can also be activated through negative thinking. Anxiety is created from negative thinking around events or situations. It’s not the events themselves that drive negative thinking but how they are perceived. The same event may have no anxiety for one person yet someone else may see this as a crisis.
Negative thinking increases anxiety and adds to overall stress levels. In Solution Focused Hypnotherapy (SFH) a metaphor called the ‘stress bucket’ is used to explain this. The bucket eventually fills with all the stress generated from negative thinking and reaches a tipping point where control is lost, to a greater or lesser extent, from the intellectual mind and passed over to the primate emotional mind. Once control has been lost, the primitive mind is now under the belief that a threat to survivability now exists and so the stress response is triggered.
The primitive mind only operates with anger, anxiety and depression as solutions. These primitive opt out clauses ensured human survival way back when but they have been adapted to modern times and are now invoked where no existential threat actually exists. The primitive mind will use one of these methods or a combination of all three as possible remedies to threats. Unfortunately, it cannot innovate and refers to previous patterns of behaviour in the hippocampus for guidance.
For instance, in the case of a depressed person, if the hippocampus suggests that survival was achieved by not interacting with the world and remaining in bed for most of the day, then this behaviour is encouraged.
In SFH clients are provided with an explanation of the stress response, usually accompanied with a suitable metaphor. Clients are also provided with information on how brain chemistry is affected and what can be done about this to return control back to the intellectual mind.
It’s important for clients to understand the stress response as often they can see parallels in their own activity which can be attributed to this. Knowing why we act a certain way is enormously beneficial when trying to change unhelpful behaviour.