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Biology of the Stress Response
Posted on January 15, 2015
To continue the series on the Biopsychosocial Paradigm of Trauma Informed Care, this post will examine the stress response. We will start with a review of the brain areas to be discussed, then move to how these areas work in collaboration to interpret and process perceived threats. Next week we’ll look at the impact of trauma on the stress response. If you are familiar with the brain, you might want to skip down to the next section.
Brain Basics
The brain is incredibly complex, and breaking it down into parts with distinct and mutually exclusive functions can be difficult, if not futile. This is due to the interactive and interconnected nature of the brain. Every part mentioned below is connected to most every other part of the brain by billions of synapses (the connections between brain cells). We’ll look at parts to understand the process, but keep in mind that each part needs to be seen as an integral component of an emergent and complex system.
In many of my past posts, we have discussed the importance of energy and information and their role in brain and mind functioning. As a reminder
- Energy: The biological activation of systems designed for a responsive action
- Information: A signal or symbol that provides context (cognitive or emotional) for something bring processed internally or in the environment
Next let’s examine how different parts of the brain handle the energy and information from stimulus in the environment (numbers correspond to the diagram below).
- Olfactory and tactile stimulus: Interestingly, touch and smells go straight to the amygdala (the emotional core of the brain). This accounts for why reactions to touch (a hot stovetop) or a smell (something rotten) seem to elicit a stronger and more immediate response than those that happen through auditory and visual stimuli.
- Auditory and visual stimulus: Sights and sounds first enter the thalamus, which decides which system (Short or High, as described below) the stimulus will be processed.
- Thalamus: Sitting in the center of the brain, the thalamus serves as the control center for visual and auditory stimulus. As the control center, the thalamus facilitates an interactive process among the cognitive, emotional, and sensorimotor centers of the brain to decide which system will handle the stimulus.
- Cortex (and Prefrontal Cortex): The cortex provides meaning to stimulus by processing it through the lens of past experiences and related memories. While the cortex serves as the outer layer of the brain, we’ll primarily discuss the prefrontal cortex. The prefrontal cortex is one of the most complex and amazing creations in the universe and is primarily responsible for making humans so successful as a species. For our purposes, we’ll simply state that the prefrontal cortex is central to our executive functioning, meaning it plays a major role in managing the processes of the brain, including reasoning, flexible problem solving, planning, memory, and aspects of emotional regulation.
- Amygdala: The amygdala manages the emotional and behavioral responses needed for survival in the face of perceived or real threats. Centrally positioned and highly connected to other brain areas, the amygdala is quick and decisive when activated.
- Bed of Nucleus of the Stria Terminalis (BNST): The main function of the BNST is to amplify the alarm response of the amygdala to the rest of the brain and body.
- Locus ceruleus: The Locus ceruleus, located between the amygdala and brain stem, actives the physical stress-based responses associated with high levels of stress and trauma, including increased heart rate, blood pressure, and sweat production.
Other key brain areas:
- Hippocampus: The hippocampus is critical in two key areas: creating memories and constructing cognitive maps of the environment. The hippocampus provides emotional meaning and data to the amygdala’s processing of stimulus. Cognitive maps play a critical role in creating a fight or flight strategy once a stimulus is deemed a threat.
- Brain Stem/Spinal Cord: The brain stem sends messages from and brings messages to the brain from throughout the body via the spinal cord and nervous system. Often thought of as primitive (or the “lizard brain”) due to its early appearance in animal evolution, the brain stem is starting to draw renewed interest for its possible role in emotions, cognitive mapping, and memories. It is impossible to examine the mind/body or brain/body connection without taking into account the critical role of the brain stem.
A. The Short Road
Adapted from Time Magazine Article by Joe Letola and Alice Park
If the thalamus interprets a stimulus as a threat or dangerous, the short road is activated (labeled A in the above diagram). Energy from the thalamus actives the amygdala, which immediately goes to work preparing the body for a physical and emotional response. The amygdala reaction includes the following:
- The hypothalamus and pituitary glands signal the adrenal glands (this relationship is often termed the HPA Axis) to release the stress hormone cortisol. If the energy is great enough, the stress hormone norepinephrine can also be released, increasing the intensity of the stress reaction even further.
- Cortisol and norepinephrine kick the sympathetic nervous system into action. Key indications of this include:
- Increased heart rate
- Increased blood pressure
- Shortness and quickening of break
- Sweat and goosebumps on the skin
- Energy and information shifts from functions, such as digestion, sex, and executive functioning, into the muscles association with the fight or flight response, primarily the arms and legs. Note: Typically, one will try to put distance between oneself and the stimulus first (flight response). If that fails, one will direct energy towards the stimulus in order to protect oneself (fight response). A third response, freeze, is activated by the parasympathetic nervous system and the dorsal branch of the vagus nerve, which shuts bodily systems down (think of the possum.) The freeze response is usually a final survival strategy, though with some survivors of abuse, especially physical and sexual abuse during childhood, this can become the default response.
In normal situations, this amygdala response will continue until the threat has passed, and can lead to amazing levels of strength and stamina. What’s important to remember when clients experience the Short Road reaction is that it is not logical, as systems such as the pre-frontal cortex are taken off line in order to maximize the energy sent to the muscles and senses. Rationalizing, negotiation, and logical thought should not be expected. Instead, focus should be put on ensuring safety for everyone in proximity and allowing the client to remove themselves from the situation whenever possible (flight response), before energy shifts towards the stress (fight response), which can often be us as helpers or other clients.
- The High Road
The long road can either create a threat response or calm one down (both represented by the B path in the diagram above). First, let’s examine how the High Road (named after the path it takes through the higher part of the brain) overrides the Short Road response.
After the fear response is activated the conscious mind eventually starts coming back online. This usually happens after the most intense part of the event has passed, but can also be activated from simple coping skills like deep breathing. Either way, a small amount of information is sent to the thalamus to interpret. If not immediately threatening, this information gets sent to the cortex (and pre-frontal cortex) for evaluation based on past experiences and memories. If the pre-frontal cortex and other executive areas believe the threat has passed, energy will start to shift from the sympathetic nervous system to the parasympathetic nervous system, which brings heart rate, blood pressure, breathing, and sweating back to normal. While the High Road can bring a return to normal, it can also intensify or start the fear response, which we’ll examine next.
If the stimulus is initially seen as benign or neutral the thalamus will, like above, send it to the cortex for evaluation based on past experience and memories. If the memory centers in the cortex connect the stimulus to a harmful event or trauma in the past, it will immediately send energy to the amygdala, and the Short Road is again activated, as outlined by the A system in the diagram. The Short Road and High Road system has served us well throughout our evolution, as it allows us to react almost immediately to sudden threats (a car swerving into our lane of traffic) and identify hidden threats that might reveal themselves over time (a stranger that seems nice but then starts to give off a creepy vibe).
This understanding of the Short and High Road sets up next week’s post on how trauma impacts these systems. In preparation for next week I wonder, with your knowledge and experience with trauma, how do you think trauma impacts the stress reaction? More science to come!
Biology of the Stress Response
Posted on January 15, 2015
To continue the series on the Biopsychosocial Paradigm of Trauma Informed Care, this post will examine the stress response. We will start with a review of the brain areas to be discussed, then move to how these areas work in collaboration to interpret and process perceived threats. Next week we’ll look at the impact of trauma on the stress response. If you are familiar with the brain, you might want to skip down to the next section.
Brain Basics
The brain is incredibly complex, and breaking it down into parts with distinct and mutually exclusive functions can be difficult, if not futile. This is due to the interactive and interconnected nature of the brain. Every part mentioned below is connected to most every other part of the brain by billions of synapses (the connections between brain cells). We’ll look at parts to understand the process, but keep in mind that each part needs to be seen as an integral component of an emergent and complex system.
In many of my past posts, we have discussed the importance of energy and information and their role in brain and mind functioning. As a reminder
- Energy: The biological activation of systems designed for a responsive action
- Information: A signal or symbol that provides context (cognitive or emotional) for something bring processed internally or in the environment
Next let’s examine how different parts of the brain handle the energy and information from stimulus in the environment (numbers correspond to the diagram below).
- Olfactory and tactile stimulus: Interestingly, touch and smells go straight to the amygdala (the emotional core of the brain). This accounts for why reactions to touch (a hot stovetop) or a smell (something rotten) seem to elicit a stronger and more immediate response than those that happen through auditory and visual stimuli.
- Auditory and visual stimulus: Sights and sounds first enter the thalamus, which decides which system (Short or High, as described below) the stimulus will be processed.
- Thalamus: Sitting in the center of the brain, the thalamus serves as the control center for visual and auditory stimulus. As the control center, the thalamus facilitates an interactive process among the cognitive, emotional, and sensorimotor centers of the brain to decide which system will handle the stimulus.
- Cortex (and Prefrontal Cortex): The cortex provides meaning to stimulus by processing it through the lens of past experiences and related memories. While the cortex serves as the outer layer of the brain, we’ll primarily discuss the prefrontal cortex. The prefrontal cortex is one of the most complex and amazing creations in the universe and is primarily responsible for making humans so successful as a species. For our purposes, we’ll simply state that the prefrontal cortex is central to our executive functioning, meaning it plays a major role in managing the processes of the brain, including reasoning, flexible problem solving, planning, memory, and aspects of emotional regulation.
- Amygdala: The amygdala manages the emotional and behavioral responses needed for survival in the face of perceived or real threats. Centrally positioned and highly connected to other brain areas, the amygdala is quick and decisive when activated.
- Bed of Nucleus of the Stria Terminalis (BNST): The main function of the BNST is to amplify the alarm response of the amygdala to the rest of the brain and body.
- Locus ceruleus: The Locus ceruleus, located between the amygdala and brain stem, actives the physical stress-based responses associated with high levels of stress and trauma, including increased heart rate, blood pressure, and sweat production.
Other key brain areas:
- Hippocampus: The hippocampus is critical in two key areas: creating memories and constructing cognitive maps of the environment. The hippocampus provides emotional meaning and data to the amygdala’s processing of stimulus. Cognitive maps play a critical role in creating a fight or flight strategy once a stimulus is deemed a threat.
- Brain Stem/Spinal Cord: The brain stem sends messages from and brings messages to the brain from throughout the body via the spinal cord and nervous system. Often thought of as primitive (or the “lizard brain”) due to its early appearance in animal evolution, the brain stem is starting to draw renewed interest for its possible role in emotions, cognitive mapping, and memories. It is impossible to examine the mind/body or brain/body connection without taking into account the critical role of the brain stem.
A. The Short Road
Adapted from Time Magazine Article by Joe Letola and Alice Park
If the thalamus interprets a stimulus as a threat or dangerous, the short road is activated (labeled A in the above diagram). Energy from the thalamus actives the amygdala, which immediately goes to work preparing the body for a physical and emotional response. The amygdala reaction includes the following:
- The hypothalamus and pituitary glands signal the adrenal glands (this relationship is often termed the HPA Axis) to release the stress hormone cortisol. If the energy is great enough, the stress hormone norepinephrine can also be released, increasing the intensity of the stress reaction even further.
- Cortisol and norepinephrine kick the sympathetic nervous system into action. Key indications of this include:
- Increased heart rate
- Increased blood pressure
- Shortness and quickening of break
- Sweat and goosebumps on the skin
- Energy and information shifts from functions, such as digestion, sex, and executive functioning, into the muscles association with the fight or flight response, primarily the arms and legs. Note: Typically, one will try to put distance between oneself and the stimulus first (flight response). If that fails, one will direct energy towards the stimulus in order to protect oneself (fight response). A third response, freeze, is activated by the parasympathetic nervous system and the dorsal branch of the vagus nerve, which shuts bodily systems down (think of the possum.) The freeze response is usually a final survival strategy, though with some survivors of abuse, especially physical and sexual abuse during childhood, this can become the default response.
In normal situations, this amygdala response will continue until the threat has passed, and can lead to amazing levels of strength and stamina. What’s important to remember when clients experience the Short Road reaction is that it is not logical, as systems such as the pre-frontal cortex are taken off line in order to maximize the energy sent to the muscles and senses. Rationalizing, negotiation, and logical thought should not be expected. Instead, focus should be put on ensuring safety for everyone in proximity and allowing the client to remove themselves from the situation whenever possible (flight response), before energy shifts towards the stress (fight response), which can often be us as helpers or other clients.
- The High Road
The long road can either create a threat response or calm one down (both represented by the B path in the diagram above). First, let’s examine how the High Road (named after the path it takes through the higher part of the brain) overrides the Short Road response.
After the fear response is activated the conscious mind eventually starts coming back online. This usually happens after the most intense part of the event has passed, but can also be activated from simple coping skills like deep breathing. Either way, a small amount of information is sent to the thalamus to interpret. If not immediately threatening, this information gets sent to the cortex (and pre-frontal cortex) for evaluation based on past experiences and memories. If the pre-frontal cortex and other executive areas believe the threat has passed, energy will start to shift from the sympathetic nervous system to the parasympathetic nervous system, which brings heart rate, blood pressure, breathing, and sweating back to normal. While the High Road can bring a return to normal, it can also intensify or start the fear response, which we’ll examine next.
If the stimulus is initially seen as benign or neutral the thalamus will, like above, send it to the cortex for evaluation based on past experience and memories. If the memory centers in the cortex connect the stimulus to a harmful event or trauma in the past, it will immediately send energy to the amygdala, and the Short Road is again activated, as outlined by the A system in the diagram. The Short Road and High Road system has served us well throughout our evolution, as it allows us to react almost immediately to sudden threats (a car swerving into our lane of traffic) and identify hidden threats that might reveal themselves over time (a stranger that seems nice but then starts to give off a creepy vibe).
This understanding of the Short and High Road sets up next week’s post on how trauma impacts these systems. In preparation for next week I wonder, with your knowledge and experience with trauma, how do you think trauma impacts the stress reaction? More science to come!
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