The brainstem serves as a relay station, passing messages back and forth between various body parts and the cerebral cortex. Many simple or primitive functions that are essential for survival are located here.
The Cerebellum fine tunes motor activity or movement, e.g. the fine movements of fingers as they perform surgery or paint a picture. It helps one maintain posture, sense of balance or equilibrium by controlling the tone of muscles and the position of limbs. The Cerebellum is critical in performing rapid and repetitive actions such as playing a video game.
The Cerebrum is the largest part of the brain. The Cerebrum initiates and coordinates movement and regulates temperature. Other areas of the Cerebrum enable speech, judgment, thinking and reasoning, problem-solving, emotions and learning. Other functions are related to vision, hearing, touch and other senses.
On the other hand, our brain is designed to function as a cohesive whole, with each region processing information. Although these regions have overlapping circuitry, we can differentiate them by their respective functions.
1) The thinking brain, evolutionarily the newest region, is the neocortex. The thinking brain engages in top-down processing – our mostly voluntary and conscious cognitive responses to our experiences (ethical choices, reasoning, abstraction, and analytical capabilities). The thinking brain has an explicit learning and memory system to support these functions.
2) The survival brain comprises the evolutionary older limbic system, brain stem, and Cerebellum. These brain regions engage in bottom-up processing – our involuntary emotional and physiological responses, including emotions, relationships, stress arousal, habits, physical sensations, vocalisations. An essential function is neuroception, an unconscious process of rapidly scanning the internal and external environment for opportunities/safety/pleasure and threats/danger/pain. To support the neuroception, the survival brain has an implicit learning and memory system – fast, automatic, and unconscious, bypassing the thinking brain.
Together, the thinking brain and survival brain comprise what many people call ‘the mind.’
Important: Awareness does not belong to the thinking brain or the survival brain. That’s why we can pay attention to thoughts, emotions, physical sensations, and the body’s position, temperature, pressure, pain.
Tai Chi training helps us learn how to direct and sustain our attention – so that we become aware of all these different body-mind experiences.
It is essential to know that the ANS is responsible for stress arousal and recovery and plays a significant role in our patterns of engagement and interaction with others.
In 1908, psychologists Robert M. Yerkes and John D. Dodson were the first to posit the Inverted U-shaped relationship between perceived stress levels and performance. Performance on a task improves as someone approaches moderate stress arousal but steadily decreases past this point until it drops off completely.
Thus optimal performance, conscious learning, and effective decision-making are most likely to occur at moderate stress levels. With this in mind, our neurobiological window of tolerance to stress arousal is how we can adjust our stress levels upwards or downwards to remain within the optimal performance zone of moderate arousal.
The optimum window lies between the Baseline and Threshold, as depicted below.
Not everybody has the same threshold, and the level will also vary for each person daily.
Depending on the situation, each person will reach their limit at a certain point.
Three pathways narrow our window. The first pathway to narrowing our window is chronic stress and developmental trauma during childhood. The second pathway is shock trauma when we experience too much stress activation or comes up too fast. And the third pathway is a challenge that goes on too long or comes up too often – leading to chronic stress. I will focus on the latter.
From
To
HPA axis activation proceeds from the hypothalamus to the pituitary gland to the adrenal glands. The hypothalamic-pituitary-adrenal axis, or HPA axis as it is commonly called, describes the interaction between the hypothalamus, pituitary gland, and adrenal glands. The hypothalamus and pituitary gland are located just above the brainstem, while the adrenal glands are found on top of the kidneys.
First, once the survival brain perceives a threat, it directs the endocrine system to release adrenaline. Within seconds, adrenaline increases our heart rate to quickly pump blood to the organs and big muscles in our limbs so that we can move fast. In the lungs, adrenaline dilates our bronchial tubes to increase our breathing rate so we can take more oxygen. Adrenaline also mobilises the body to release glucose, so we’ll have a ready source of energy.
At the same time, blood flow shifts away from the digestive system, which we may experience as nausea or butterflies in the stomach. Adrenaline also constricts the blood vessels supplying our skin. That’s why our skin may feel cold and clammy, and our palms may get sweaty.
Everything about stress activation is initially aimed at transporting oxygen and glucose since we need energy and brain focus right now.
After the first wave, the survival brain and HPA axis controlling stress hormones work together to adjust our stress level to correspond with the particular stressor. Now the HPA axis provides a finetuning second wave of stress activation. The HPA axis will amplify stress activation if we still perceive a threat. Thus, whether we perceive ourselves as having agency in the situation plays a critical role in our second wave of stress activation.
The most crucial energy-mobilisation hormone is cortisol. Cortisol has two jobs during the second wave. First, it replenishes energy stores that got depleted during the first wave’s adrenaline rush. Second, cortisol boosts immune functioning.
The HPA axis also activates other hormones that prioritise immediate needs:
- Endorphins that blunt our perception of pain,
- Vasopressin regulates the cardiovascular system,
Conversely, the HPA axis inhibits hormones related to long-term needs, like
- Growth hormone
- Sex hormones (estrogen, progesterone, testosterone)
- Insulin to inhibit energy storage
Later, after the stressor has passed, it activates hormones to facilitate recovery. During both the second wave and recovery, the HPA axis works with the immune system and the autonomic nervous system (ANS)
Simplifying the Polyvagal chart and changing the time axis back to the performance axis as in the Flipped Yerkes-Dodson curve gives me the following picture:
However, this is only half of the complete story. Whenever the survival brain neurocepts safety, we’re inside our window of tolerance. Inside the window, we can access all the nervous system branches in ‘well-being mode’. This gives the following graphical view:
When viewing the same info but with split up between the three different ANS branches, it leads to the following overview:
Without adequate recovery after chronic stress, the mind-body system remains activated and doesn’t return to its regulated equilibrium. When the allostatic load accumulates, we can experience a range of physical, emotional, cognitive, spiritual, or behavioural symptoms.
Allostasis happens through communication between (1) the brain; (2) the autonomic nervous system; (3) the immune system; and (4) the endocrine system, especially the HPA axis, which controls the stress hormones. Thus, the allostatic load can manifest as imbalances or malfunctioning in any of these four systems.
In other words, dysregulation can affect all aspects of our mind-body system – and thus manifest as a range of cognitive, emotional, physiological, spiritual, and behavioural symptoms.
So it is time to see what solutions we can offer you. Read more in my next blog