Queen Amygdala
The limbic systems is the part of the brain that operates the autonomic nervous system (ANS). In evolutionary terms, it is the oldest structure in the brain, and one that we have in common with our mammalian ancestors. The limbic system acts as a trauma control centre; in this role, it regulates fear conditioning and memory storage - the two processes central to our reactions to trauma. The specific parts of the limbic centre that operate these processes are the amygdala and the hippocampus.
The amygdala is the brain's gatekeeper for incoming emotional information. Located at the top of the brainstem, it controls a variety of brain functions - most notably emotional memory, fear and anxiety. In particular, it assesses incoming information for its emotional significance. People whose amygdala is damaged lack the ability to judge the emotional significance of events. They remain as impassive when confronted with threatening events as when they are facing pleasant situations.
Harry "Breaker" Morant
In everyday circumstances, information is passed from the amygdala to the frontal cortex, where higher-order thinking takes place. But under threatening circumstances in which speedy reaction time is essential for survival, the amygdala takes a 'short cut' and alerts the hypothalamus directly. In response, the hypothalamus releases a chemical called corticotropin-releasing factor, which, in turn, stimulates the release of adrenocorticotropin hormone from the pituitary gland. This hormone then stimulates the adrenal glands release of cortisol, which activates the SNS (sympathetic nervous system) and gets the body ready for fight or flight. Conversely, in situations where neither flight nor fight is possible, the limbic system actives the PNS (parasympathetic nervous system) and the body goes into the submission state known as tonic immobility.
Gin & tonic immobility
The amygdala is like a smoke detector for the brain. In an emergency it runs the show, making decisions before they are filtered through conscious awareness, compelling us to respond before we have time to think. Responses triggered by the amygdala are automatic and reflexive: soldiers who fall to the ground immediately upon hearing a car backfire are being led by their amygdala. Their training and battlefield experience has kicked in, beyond any conscious control.
If the amygdala is to take centre stage, however, it must 'inform' other parts of the brain to shut down - specifically, brain structures such as the hippocampus (the part of the brain that stores memories of time and space, orders memories along our life's timeline and makes connections between memories) and Broca's area (the part concerned with translating emotional experiences into language). These mechanisms are too time-consuming at a time when immediate reactions to the current situation are necessitated.
Under normal circumstances the hippocampus plays an important role in processing and storing memories. It is believed to act like a USB cable that transfers information from the right side of the brain (where information is held as it actively awaits processing) to the left side (where it is stored in memory). In contrast to the amygdala, the hippocampus is associated with a conscious, explicit, verbal route to learning and the storage of memories. When someone is rehearsing a talk or planning a travel route, it is the hippocampus that is responsible for transferring memories into long-term storage.
During trauma, however, the activity of the hippocampus is suppressed. Many scientists believe that this outcome is related to excessive stress, which kills neurons in the hippocampal pathway. It is as if a fuse has blown in the brain, shutting down the usual transfer of information. In these circumstances, memories lack detail.
In normal circumstances, memories are filed away as representations of past events. But following trauma, they remain in an active state, and thus seem to float in the present. At the same time, they are difficult to talk about coherently: an overload of information is associated with the traumatic experience, information that the individual is unable to manage. In many cases, traumatic memories are filed away over time. When this does not happen, the re-experiencing symptoms of PTSD are the result.
German officials examine the pile of abandoned luggage left on the platform after the departure of a deportation train on its way to the Belzec death camp
In short, PTSD is a disorder of information processing. The PTSD sufferers' traumatic memories remain active because the brain structures concerned with memory storage and language have shut down, leaving the individual 'on alert' until these parts of the brain are reactivated. It usually takes around a month for the brain to repair the 'blown fuse' in the hippocampal pathway, so that the usual memory-processing mechanisms can come back on line. For some people, however, it takes longer. This difference could be due to a number of factors, including natural variations in the capability of the hippocampal pathway, the occurrence of other traumatic events that subsequently slow the repair process or continued activation of the amygdala, even though the danger has passed.
An intriguing possibility suggested by research is that vulnerability to PTSD has its roots in the early years of childhood. During a period when the brain is still forming, a lack of parental care or other stressors can alter the neural systems responsible for cognitive-emotional processing of traumatic information, leading to a reduced hippocampal volume. One implication of this finding is that some people are more susceptible to PTSD than others because they file their memories away less efficiently. Another is that they have traumatic memories from early childhood that are reactivated by a later trauma, in which case the memories would be old ones that were laid down before language was formed. This would explain why some PTSD sufferers experience disorganised and distressing mental states that they are unable to meaningfully 'pin-down' to actual events in their lives, leading, in turn to difficulty processing their current situation.
A butterfly made perfect by a dart through it
Sabian Symbol
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Text source: What Doesn't Kill Us: the new psychology of post-traumatic growth, Professor Stephen Joseph, p.55-57.
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