In addition to the role of associative fear structures in the development of PTSD symptoms after having suffered a trauma, the associative fear structure perspective
1 Additionally, avoidance or flight behavior can be part of the fear structure, too.
provides some assumptions about the chronification process of PTSD. These determinants will be outlined in the following paragraphs.
The vicious circle of triggering – reactivating – enlarging of associative fear structures The described process of enlarged fear structures can occur in “every day life” but is enhanced during traumatic experiences or experiences with a strong emotional component. While the number of (hot) elements in the fear structure increases, the probability of co-activation (and therefore inclusion) of autobiographical (cold) memory decreases: Elbert et al. (2006, p.8) state that typically “only one context in which the fear network was previously activated” can be retrieved at the time. This is true because we know that we cannot be at two places simultaneously or build up a single memory from two different episodes. Consequently, the more different experiences are included in one large (fear) network, the lower the probability that a respective cold memory trace (about when and were) is co-activated and connected with the network. Within this logic, the “end-product” is a large structure of hot memory elements with very strong interconnections. The whole structure is easily triggered by every kind of cue (intern and extern) and without explicit connections to a single episode with clear information about the cold facts. This “free-floating” memory system is able to reactivate within very short time windows a very realistic feeling of life threat and whatever else was included in the traumatic experiences.
The model of the enlarging fear structure due to subsequent traumatic experiences and recollections is encouraged by the evidence of the building block as described by Neuner and colleagues (2004) and Schauer et al. (2003). Neuner et al. (2004) claim that any individual could develop PTSD regardless of other risk factors as long as he/she encounters enough traumatic experiences. This strong statement is based on PTSD prevalence findings in a huge sample of several populations (West Nile regions, refugees from the civil war in southern Sudan, Sudanese nationals and Ugandan residents, Neuner, 2003). Very high individual numbers of traumatic events were reported in this sample. A significant correlation was found for the number of different event types of traumatic experiences and the number of PTSD symptoms. The analysis of different event types considers the fact that it is often too difficult to reliably name the exact number of distinguishable traumatic experiences within war survivors.
Can fear structures of single traumata enlarge, too?
The fear structure perspective also accounts for single traumatic events: As shown in fear conditioning studies, a single traumatic event might lead to a fear network, but it will be relatively connected to contextual information. Only with later reactivation without activation of the context or future traumatic experiences, the network will be more and more separated from the autobiographical information and thus resemble more and more an associative network with the common element of fear, threat and cognitive as well as physiological responses.
In summary, the vicious circle of pathologically encoded traumatic experiences inhibits helpful inclusion and maintenance of context information of the original situation and strengthens the pathological structure. This pathological spiral explains why the easily reactivated associative (fear) structure and the inherent here-and-now-quality easily lead to a PTSD chronification.
As the missing connection between fear structure elements and the autobiographical memory seem to also play a role in the chronification process of PTSD, some explanations for this phenomenon should be given in addition to the hippocampal theory outlined above.
The role of retrieval strategies in the chronification process
Ehlers and Clark (2000) argue that the missing connections to the autobiographic memory and the bad elaboration of the autobiographic memory might be due to retrieval strategies. Two ways of retrieving stored autobiographic episodes are possible: higher-order strategies based on the impact of the episode (e.g. memories of the first day in school) and retrieval on the basis of triggers associated with a special event.
Some authors (e.g. Conway & Pleydell-Pearce, 2000; Ehlers & Clark, 2000) argue that the majority of “normal” processing of autobiographic episodes aims to reduce the unwanted retrieval in order to facilitate every day activities without “intrusions” from past events. The authors suggest that autobiographical events are normally embedded in a memory system which is organized on different levels of specifity: lifetime periods, general events and event-specific knowledge (Conway & Pleydell-Pearce, 2000).
“Lifetime periods” refer to general knowledge of the special period in one’s life, for example of significant others involved, activities, plans or goals, summing up in thematic and temporal knowledge about common features of that period (e.g. “When I was in primary school”). Compared to that, “general events” refer to a more specific
activity, but not necessarily to a single one. The term may either apply for special events like “my driving test” or repeating events like “concerts with my orchestra” as a set of associated events. “Event specific knowledge” stands for the specifying information about a situation or episode on the level of autobiographic memory. Conway and Pleydell-Pearce (2000) point out that the above mentioned information about traumatic experiences comprised in a fear structure are an extreme example of event specific knowledge. This knowledge may or may not (see below) be related later with more abstract general event and lifetime period knowledge.
The organization of the autobiographic memory as proposed by Conway and Pleydell-Pearce (2000) is assumed to facilitate arbitrary retrieval including specific information of a single event as well as general information with respect to living conditions and time period in which the event occurred. On the other hand, this way of organizing the autobiographic memories inhibits involuntary intrusions triggered by a cue associated with past events. Thus, in „normal“ processing of past events, the first retrieval strategy (on the basis of higher-order categories) is fostered and the second (triggered by associated cues) is inhibited.
In case of PTSD, the memory of a traumatic experience is assumed to be badly organized and not sufficiently integrated in temporal and spatial context as well as previous and subsequent events as described above. Thus, the arbitrary retrieval on the basis of higher order categories becomes difficult. Instead, involuntary intrusions without clear temporal or other structuring information but with “here-and-now-quality”
are enhanced due to the large fear network. This re-experiencing of the same event in a variety of contexts leads to a retrospective inclusion of contextual information into the representation of the original event.
Additional remarks from learning theory
Ehlers and Clark (2000) add two aspects with respect to stimulus-stimulus (s-s)-and stimulus-response (s-r)-association learning which explain the frequent persistence of PTSD.
The building of s-s- and s-r-associations (which are all included in the fear structure) is known to enable predictions about what happens next in a specific situation. Furthermore, this mechanism is particularly prominent for stimuli, which already had a high predictive value for the life threatening situation (Foa & Kozak, 1986). Consequently, even stimuli which were present in advance to the life threatening
situation become associated with the life threat and are interpreted as such a predictor in PTSD patients.
As the retrieval of a memory due to s-s- or s-r-associations is not arbitrary or intentional, PTSD sufferer often do not realize that emotional reactions in an everyday situation are part of the traumatic memory. Especially in cases, when the fear structure is partly reactivated including the emotional responses, the sufferers have difficulties in realizing that they are not longer in a dangerous situation. This phenomenon is called
“affect without recollection” (Ehlers & Clark, 2000, p. 324), a common problem in maintaining the pathological associative memory structures.
Additionally, Ehlers and Clark (2000) suggest a very strong perceptual priming for stimuli temporally associated with the trauma, that is a lower perceptual threshold for these associated stimuli. In consequence, trauma-associated stimuli are more easily recognized by PTSD patients. But the representation of the associated stimulus is often very inexact as these implicit retrieval strategies are not well elaborated. Hence, even a small similarity to the associated stimulus is sufficient to appraise the present stimulus as trauma-associated, too. That is, the low perceptual threshold for trauma-associated stimuli is unfortunately endorsed by a low stimulus discrimination (Ehlers & Clark, 2000).
This section pointed out a number of mechanisms within the fear structure perspective that explain the high number of PTSD chronification. The next section will shortly draft conclusions that can be derived for PTSD treatment to prevent a fatalistic view of PTSD. As this is not of central interest for the current dissertation, ideas will be mentioned very briefly.