Applying Memory Concepts
The memory recalled by PTSD survivors (PTSD memory) shares many features with implicit memory. Like implicit memory, it is characterized by limited accessibility due to declared memory gaps and is characterized by deficits in intentional recalling of important peripheral sensory and self-meaningful details about the trauma (Herlihy, Scragg, & Turner, 2002; Tuval-Mashiach, Freedman, Bargai, Boker, Hadar, & Shalev, 2004). PTSD memory reports are often distinguished from the memory of asymptomatic trauma survivors by their confusion about the traumatic event’s temporal order and incoherence (Foa, Molnar & Cashman, 1995; Hembree & Foa, 2000). They are also characterized by having perceptually driven flashbulb or hotspot qualities, as intrusive trauma perceptions are often reexperienced involuntarily and unintentionally with a good deal of arousal and distress in isolation of their traumatic context (Ehlers, Hackmann, & Michael, 2004; Berntsen & Rubin, 2006). Abreactions as such according to neuroimaging findings are enhanced by hippocampal activations suggesting its role during intermediate consolidation processes (Osuch, Benson, Geraci, Podell, Herscovitch, McCann et al., 2001). PTSD traumatic memory is behaviorally inferred in its reported symptoms of avoidance, arousal, dissociation, and in its “unintended” reliving of sensory emotional fragments of the trauma (van der Kolk & Fisler, 1995). This also suggests a supportive role for the hippocampus, for as noted in the triple dissociation studies earlier, lesioning the striatum allows expression of hippocampal tendencies for the unintentional retrieving of previously learned behavioral sequences (DeCoteau & Kessner, 2000; Packard & McGaugh, 1996). Traumatic manifestations are also behaviorally inferred. Unbeknownst to the PTSD survivor traumatic memory can be represented in harmful aggressive behaviors to self and others, in the cyclical revictimizing of oneself or others (Marx, Heidt, & Gold, 2005; van der Kolk, 1989) and in producing persistent victim identification with aspects of the trauma, e.g. compulsion for dressing and identifying with one’s prior military experience two decades later (McNally, Lasko, Macklin & Pitman, 1995; Berntsen & Rubin, 2006). PTSD memory is also modality specific and data driven. A fragment of a single perceptual experience such as a trigger can elicit a portion of the traumatic memory, much in the way that priming-induced fragments can elicit perceptual recognition for pattern completion (Michael, Ehlers, & Halligan, 2005) or presentation of the CS can elicit an association with an aversive US.
In contrast to fear conditioning, implicit responses to traumatic stress are fast learning; a single session of traumatic stress can overwhelm and reverberate thought processes despite attempts at traumatic thought avoidance. As noted above this is probably due to fast-learning hippocampal mediated intermediate consolidation involvement. Like fear conditioning PTSD perceptual memory is also multi-modal
PTSD symptom expression is often slowly acquired, necessitating as much as three months for assuring chronic symptom establishment and memory impairment (American Psychiatric Association (APA), 1994; Bryant & Harvey, 2002). Furthermore thought suppression and traumatic forgetting processes supporting avoidance symptom expression, are probably implicit processes as well, as memory and intentionality of their intial use is not recallable and consciously accessible. Their use however is behaviorally inferred and evidenced in later peripheral and contextual memory deficits with regards to the trauma. Previous discussion can be summarized below.
Characteristics of PTSD Memory
| Implicit | Explicit |
|---|---|
| 1. PTSD memory has limited accessibility, necessitating perceptual triggers reminiscent of the trauma. When present the traumatic trigger can elicit a representative portion of the traumatic memory facilitating perceptual recognition and traumatic pattern completion. | 1. In contrast to fear conditioning traumatic and PTSD memories are fast learning. A single traumatic session overwhelms the brain and central nervous system and probably interferes in consolidation processes. |
| 2. PTSD memory is characterized by deficits in intentional recollection, trauma narrative coherence, and temporal order. | 2. In contrast to fear conditioning paradigms, which employ healthy subjects, research studies monitoring PTSD reactions use healthy controls, asymptomatic and PTSD symptomatic subjects. |
| 3. Trauma memories are reexperienced as perceptions having sensory flashbulb or hotspot qualities. | 3. The involuntary reliving and retrieval of trauma-related sensory memory is likely mediated by a functionally intact hippocampus (in accordance with the findings from triple dissociation studies noted earlier). The process of reliving is an explicit process; however in PTSD this reliving is often involuntary (i.e. during abreactions or during nightmares reminiscent of the trauma) and therefore reflective of implicit processes. |
| 4. PTSD symptoms are behaviorally inferred in symptoms of avoidance, arousal, dissociation, and unintended reliving of sensory emotional traumatic fragments. | |
| 5. Survivors with PTSD symptoms can unknowingly and unintentionally reexperience implicit behavioral perceptual-motor-emotional aspects of the trauma by inadvertently victimizing others or seeking out masochistic relationships that victimize the self. | |
| 6. PTSD symptom expression is often slowly acquired, necessitating at least three months for assuring chronic symptom establishment. | |
| 7. Thought suppression mediating traumatic avoidance behaviors are likely implicit processes, as their initial cognitive-behavioral strategy, selection, and use are not easily recallable. |
According to this analysis one can conclude that PTSD traumatic memory and symptom expression shares many features with implicit memory. Its fast learning quality is probably mediated by hippocampal processes, which as noted earlier enhance implicit learning processes, and are likely reflective of mid-consolidation process effects.
According to the multiple memory systems model, the striatal behavioral and amygdaloid motivational stimulus-response systems and cortical perceptual system (singly and in interaction) are probably biased expression in PTSD. Hippocampal mediated reactivations in these regions can account for PTSD memory’s implicit features of involuntary perceptual reexperiencing of traumatic sensory fragments and traumatic emotion like fear as well as behavioral reliving and identifying with traumatic material. Impairments or disruptions in traumatic memory’s ability for intentional and declarative recall and retrieval of a cohesive trauma narrative suggest contextual deficits in hippocampal functional integrity.
References
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