damn, PTSD is a complex disorder. really. i’ve been pursuing some personal interest reading on the subject (light, because i don’t exactly have a lot of free time lately but i am curious), and found myself surprised at just how much physiological disturbance can be behind the symptoms that i and others cope with.

as someone whose research touches on learning and memory, i thought this would be a good exercise for myself and for my future thesis. i’m taking a dive into what makes old memories continue to throw down on your attempt at normal life well after you’ve coped with the immediate trauma and possibly changed your entire life circumstances and moved across the country to try to start fresh.

to get started, let’s talk about what PTSD is and why it’s a problem we need to know more about. the DSM-IV defines PTSD as such:

Diagnostic criteria for 309.81 Posttraumatic Stress Disorder

A. The person has been exposed to a traumatic event in which both of the following were present:

(1) the person experienced, witnessed, or was confronted with an event or events that involved actual or threatened death or serious injury, or a threat to the physical integrity of self or others
(2) the person’s response involved intense fear, helplessness, or horror. Note: In children, this may be expressed instead by disorganized or agitated behavior

B. The traumatic event is persistently reexperienced in one (or more) of the following ways:

(1) recurrent and intrusive distressing recollections of the event, including images, thoughts, or perceptions. Note: In young children, repetitive play may occur in which themes or aspects of the trauma are expressed.
(2) recurrent distressing dreams of the event. Note: In children, there may be frightening dreams without recognizable content.
(3) acting or feeling as if the traumatic event were recurring (includes a sense of reliving the experience, illusions, hallucinations, and dissociative flashback episodes, including those that occur on awakening or when intoxicated). Note: In young children, trauma-specific reenactment may occur.
(4) intense psychological distress at exposure to internal or external cues that symbolize or resemble an aspect of the traumatic event
(5) physiological reactivity on exposure to internal or external cues that symbolize or resemble an aspect of the traumatic event

C. Persistent avoidance of stimuli associated with the trauma and numbing of general responsiveness (not present before the trauma), as indicated by three (or more) of the following:

(1) efforts to avoid thoughts, feelings, or conversations associated with the trauma
(2) efforts to avoid activities, places, or people that arouse recollections of the trauma
(3) inability to recall an important aspect of the trauma
(4) markedly diminished interest or participation in significant activities
(5) feeling of detachment or estrangement from others
(6) restricted range of affect (e.g., unable to have loving feelings)
(7) sense of a foreshortened future (e.g., does not expect to have a career, marriage, children, or a normal life span)

D. Persistent symptoms of increased arousal (not present before the trauma), as indicated by two (or more) of the following:

(1) difficulty falling or staying asleep
(2) irritability or outbursts of anger
(3) difficulty concentrating
(4) hypervigilance
(5) exaggerated startle response

E. Duration of the disturbance (symptoms in Criteria B, C, and D) is more than 1 month.

F. The disturbance causes clinically significant distress or impairment in social, occupational, or other important areas of functioning.

it’s bad news when unwanted memories take over your entire life. this is stuff that should be put away, feelings of fear that should be extinguished. things that remind me of the negatives of my past are banished from my life, but when they show up things get very ugly inside my head. one particularly devastating event caused me to dissociate for days. i find anything related to the subject of the incident almost violently upsetting. sleep is no escape when i’ve reached that point- i either do not sleep or i have deeply disturbing dreams. this is no cakewalk, when things get like this, i become only marginally useful. i nearly flunked out of high school, because i had very little sense of the future. logically, i knew the days would continue. my brain refused to believe it. the college acceptance letter and a long heart-to-heart with a friend who convinced me to start fresh somewhere new, those are among the reasons i continued to where i am today.

personal sharing aside (i just wanted to convey the real life side rather than the clinician’s list), let’s get down to the science of this beast. a big player in the learning and memory arena is the hippocampus. this seahorse-shaped part of your brain is generally involved in a few different areas of memory detailed below:

semantic memory- meanings of words, in general declarative facts. example: there are 50 stars on the flag of the USA.

episodic memory- experiences and events. example: i voted in the last election.

also spatial memory- spatial orientation. example: to get to work every day, i use spatial memory to navigate my vehicle to the correct location.

the hippocampus is also active during several types of associative tasks- for example, when associating a name and a face when you meet somebody new. it is finally a major processing center, integrating many types of information into logical chunks as the information flows through the major pathways. we can conclude that the hippocampus is extensively involved in processes that could respond to a traumatic memory.

there are two other big players that the PTSD field are investigating: the amygdala and medial prefrontal cortex. the amygdala is required for fear conditioning- one could see this as a player in PTSD from that alone. the mPFC regulates the amygdala, and is involved in emotional and working memory. i’m not covering all the bases on these regions, but we can see where the roles they play would be very interesting in the context, right?

i discovered an excellent review here of a potential model for PTSD. i think that what they propose makes a lot of sense and as such i will summarize here.

first, the PFC’s role. as it is affected by stress, and the hormone noradrenaline, it may not properly regulate (read: inhibit) the function of the amygdala. the amygdala enhances fear conditioning during a stress response- i would venture to guess this conditioning would be harder to extinguish than one derived from a non-life-threatening situation. and that brings us to the hippocampus. the hippocampus is exquisitely sensitive to cortisol- another stress hormone. since we know the myriad of vital information processing functions this structure handles, a disruption in proper functioning can cause all kinds of chaos.

here you have a recipe for a trigger causing an associated memory and the conditioned fear response. you have the defects in processing that could cause fragmented memory or amnesia- or maybe even the somewhat loose associations that make a lot of things in real life into memory/flashback triggers. it’s an interesting look at how these processes work together- but it is far from a complete explanation. this review article from 2002 is the most recent i could find with such a well-fleshed-out proposed model- though both of the authors have been quite active since then. they both do some very cool work and i hope they continue to break down the barriers to understanding this problem.

final note, since the hot topic on a couple of scienceblogs has been sex differences… females are more prone to developing PTSD after a traumatic event than males are.