Science of Trauma 2: The Limbic System
This is Part 2 of my series on understanding the science of trauma. Here I will be explaining a little more about the mammalian area of the brain also known as the limbic system and how it responds to trauma.
The limbic system is the emotional centre of the brain and plays a very important part in memory. Jaak Panksepp in his book Affective Neuroscience details his research in mapping emotions in the brain. He noted that there are 7 emotional circuits that can be activated; SEEKING, PLAY, CARE, LUST, FEAR, GRIEF/PANIC and RAGE within the limbic system. Like a muscle, the more we use the circuits the stronger they get. When the FEAR, GRIEF/PANIC and RAGE circuits are activated they release chemicals such as cortisol into our bloodstreams. Whilst a small amount of stress is good e.g. nervous about learning to swim, having really high levels for long periods of time can cause issues.
The Limbic System Under Threat
When understanding how our bodies respond to trauma we’ve got to understand the limbic system a little more. The diagram above shows some of the different parts. What I’m explaining below is the chain if reactions that kick start the ‘Fight or Flight’ response. The ‘fight or flight’ response is when the body has physical responses to deal with threat. The difficulty is that our bodies don’t know the difference between physical threat and psychological stress. There is also a ‘freeze’ response that uses a different pathway. I’ll talk about Flight, Fight, Freeze more in a different post.
Hippocampus: The hippocampus is really important for forming, organising and storing memories. It’s also linked to emotions as it creates links between emotions and sensory information-be it sights, sounds and smells. The hippocampus can be significantly impacted by trauma. Sights, sounds, smells will be linked to the traumatic memories. However, when we experience trauma we have a lot of cortisol and noradrenaline in our systems, these hormones stop the hippocampus from filing memories correctly. Usually memories have a date stamp- you know when they’ve happened (or can give a rough idea). But when trauma happens the memories are filed without a date stamp. So when the memories are recalled they feel like its in the present, happening all over again. These are called flashbacks. You feel all the same terror and fear you felt at the time of the memory and the body responds in the same way- alerting the amygdala and releasing all the hormones (see below).
Amygdala: The amygdala works out the emotional meaning of everything that happens to a person. It’s key part of the RAGE and FEAR emotions. It acts like a smoke detector- once it senses threat it sets off the alarm bells. Unfortunately it often doesn’t know the difference between psychological threat and physical threat. When it sets of the alarm signal it’s important for the cortex to turn off the amygdala if it knows its a false alarm. After trauma the amygdala can become oversensitive and acts without thinking (involving the cortex) so sends messages straight to the hypothalamus instead, starting a chain of reactions.
Hypothalamus: The hypothalamus is a very busy part of the brain. With the information it is given it acts like a thermostat trying to get the body to it’s set point. It controls areas of the autonomic nervous system as well as the pituitary glands. When the amygdala tells it there is a threat it releases a hormone called ‘CRH’ (corticotrophin-releasing hormone) which stimulates the pituitary gland.
Pituitary Gland: The pituitary gland is small but mighty. It has the power to release a range of hormones, from itself to different parts of the body to tell them to do stuff (or release yet more hormones). You can imagine these chain reactions of hormones like dominoes cascading. When the hypothalamus sends the CRH hormone its way, the pituitary gland sends a message to the adrenal glands (just above the kidneys) to start releasing cortisol. The cortisol washes all over the body which starts a whole load of reactions in the body. The adrenal glands also produce adrenaline and noradrenaline.
The Impact of Releasing Cortisol
Cortisol is usually released early in the morning- it has a peak about 30 minutes after we wake up then gradually falls again, there is another peak in the afternoon before getting low again in the evening. It’s at it’s lowest in the early hours of the morning when we’re sleeping. When we are constantly under a lot of stress or experience traumatic flashbacks that kick our ‘flight or fight’ response into gear, our bodies start to produce cortisol a lot more than usual and this curve (known as the HPA axis) is flattened as there is more cortisol in the body throughout the day. This can lead to difficulties sleeping, issues with our immune systems as well as mood issues such as depression- not just for those experiencing traumatic stress, but other constant stress too.