PTSD (RDRM (Brewin (2010) revised DRM - object and spatial representations…
Brewin (2010) revised DRM - object and spatial representations are stored in 2 forms:
- 1) Sensation based representations (S-reps) = egocentric, viewpoint-dependent. These store unprocessed sensations and are automatically registered-->these are what are reactivated as flashbacks
- 2) Contextual based representations (C-reps) = retrieved
allocentric, viewpoint-independent. These store abstract properties so that they can interact with existing data. They require conscious attention to be registered and can then be retrieved deliberately or automatically
- Translation processes normally integrate the two representations, which may give rise to field versus observer images
- Pathological encoding from stronger S-reps (dorsal stream), which function extremely well and efficiently, whilst dys-regulating C-reps (ventral stream), with much less connection between the structures.
- Normal visual recall is driven top-down by C-reps, with the generation of egocentric visual imagery allowing reactivation of matching information contained in S-reps.
- Pathological retrieval from automatic recall of very strong S-reps (driven bottom-up based on situational cue), without any strong associated C-reps that provide temporal context (why experience as happening in the here and now
- C-reps supported by the classical MTL system for declarative memory (Squire & Zola-Morgan, 1991), including the hippocampal provision of the spatio-temporal contextual information associated with an episodic memory for an event.
- Have association with semantic memory = can be used to generate meaningful interpretations of an event, abstracted or “gist” representations, and novel images that combine object and conceptual information in flexible ways, e.g. as images from nonexperienced viewpoints.
- include the spatial layout of the scene comprising the event (i.e., its spatial context), encoded as allocentric representations in the hippocampal and parahippocampal regions.
- Required process of translating scene info between egocentric and allocentric reference frames is assumed to be supported by the retrosplenial and posterior parietal cortices, with imagery supported in the precuneus.
- In healthy p's, the S-rep for an extreme event is associated, via higher level representations in the precuneus, to a corresponding C-rep in the MTLs. The association to the corresponding C-rep has two consequences:
(a) allowing the event to be correctly integrated with its semantic and autobiographical context --> preventing it from being reexperienced in the present
(b) allowing for increased top-down control via connections from the prefrontal cortex to the MTL, such as the provision of specific retrieval cues, verification of the products of retrieval, strategies for disambiguating events with similar contexts, and deliberate suppression of retrieval if required (Anderson et al., 2004).
Genration of intrusive image:
- Long-lasting S-reps (formed by emotionally salient experiences) retrieved by corresponding emotional states/sensory cues in the environment. This sensory reliving component is given a context and modulated by activation of the corresponding C-reps. Images in the precuneus formed from C-reps may involuntarily activate associated S-reps that contribute additional sensory and emotional aspects to retrieval.
e.g. a depressed person might have a negative thought about being rejected that was associated with a C-rep of a time when he or she was jilted by a lover. Activation of the C-rep could then trigger the reactivation of an associated S-rep that would contribute sensory details of the rejection event, along with associated feelings of anger and despair.
- Consistent = visual memories of upsetting episodes have been observed to intrude into the verbal ruminations of depressed individuals (Pearson et al., 2008)
- As part of the process of deliberately simulating possible future outcomes, some individuals will construct images (e.g., of worst possible scenarios) based on information in C-memory and generate images in the precuneus. These images may be influenced by related information held in C-memory or in addition the images may be altered by the involuntary retrieval of related material from S-memory.
- High levels of stress have deleterious effects on hippocampal functioning while simultaneously potentiating amygdala functioning (Payne et al., 2006) --> this should produce strong S-reps but weaker or impoverished C-reps (supported by hippocampus).
= flashbacks in PTSD result from the creation of an S-rep without the usual association to a corresponding C-rep.
Bisby et al. (2010)
- Looked at effect of alcohol on intrusive memories, whether there is a selective effect for allocentric (C-reps) whilst leaving egocentric memory intact (S-reps)
- Double-blind study, 48 p's received low or high does of alcohol or placebo drink prior to watching a trauma films. Virtual environment was used to present objects and test recognition memory from the same viewpoint as presentation (tapping egocentric memory) or a shifted viewpoint (tapping allocentric memory).
Intrusions over the next week assessed with diary.
- More intrusions in low dose compared high and control
- Low dose of alcohol affects switch-view (allocentric) but not same-view (egocentric) memory --> suggests the increase of trauma video intrusions seen in the low dose condition results from impairment in allocentric memory
- Worse allocentric memory performance on the VR task (controlling for egocentric memory performance) predicts more subsequent intrusions of the trauma video
= suggests allocentric (S-reps) involved in intrusive memories
- BUT, ecological validity? to what extent does the trauma video paradigm reflect a real life trauma --> is it different for different types of trauma i.e. it fills DSM criteria in that p's witnessed a death or injury BUT what if the traumatic event in real life is physical not viewed?
- p's used were healthy, not PTSD --> baseline responses to flashbacks may be different in PTSD and healthy controls
Normal recovery process:
So what goes wrong in PTSD?
- Traumatic info laid down as C-reps (limited) and S-reps --> over next few days flashbacks lead to copying of extra info stored as S-reps, contextualising it within C-reps and linking it to corresponding S-reps
- Limited capacity system means little info transferred at one time.
- C-reps locate context and time of the event, and cues trigger both S-reps and C-reps. S-reps and C-reps compete for retrieval and - if good match to S-reps – C-reps begin to inhibit fear system
- Consolidation of contextualised memories in neocortex leads to long-term inhibition
- C-reps do not make a good copy of the information stored as S-reps deliberate avoidance
- Information remains isolated as S-reps
- When S-reps are triggered the fear system is not inhibited
Parallel neural systems identified for visual information:
- 1) Ventral stream = V1 --> inferior temporal cortex
interacts with medial temporal lobe structures such as the hippocampus and parahippocampus that provide contextual information, as well as with the amygdala
- 2) Dorsal stream = V1 --> superior parietal cortex
interacts particularly with insula and amygdala
- Both streams project to precuneus in medial parietal lobe where images can be visualised
- Information from both streams is normally integrated via pathways involving retrosplenial cortex
Brain abnormalities in PTSD:
- Abnormalities found, mainly reduced volumes in frontal and limbic areas, are similar to those implicated in MDD -> raises q of whether they correspond to specific PTSD characteristics of reflect common difficulties e.g. emotion regulation (Drevets et al. 2008)
- Consistently found in meta-analyses of structural MRI studies that there are reductions in brain volume for PTSD p's e.g. Karl et al. (2006) --> also found reduction in left amygdala and in the frontal cortex (not hippocampus)
- Unlike other anxiety disorders and major depression, not core symptoms that are essential for PTSD diagnosis in DSM= individuals have to report symptoms from clusters means individual clinical presentations could vary widely/creates diagnostic heterogeneity
Whaley et al. (2013) p's asked to write a trauma narrative and under fMRI indicate what items related to OM and flashbacks out of a list of OM, flashback and foil items
- Flashback specific increases in right insula & supplementary motor area, and left pre central cortex and mid-occipital gyrus
- SMA and left pre central cortex part of dorsal stream = flashbacks characterised by increased activity in this stream, and hyperactive S-reps in flashbacks
(possible that increased activity reflects preparation to act on a threatening environment --> interesting for future research)
- Flashback specific decreases in right precuneus and left parahippocampal gyrus --> less activity in allocentric memory areas consistent with underachieve C-reps
- Limitations: 1) p's variety of trauma types and durations --> findings attributable to variations in trauma, 2) not all p's experienced flashbacks in scanner --> findings might extend only to thinking about flashbacks, 3) don't know behavioural responses --> decreased precuneus activity reflects increase in avoidance not decreased C-rep input?
- Future: bigger sample so can do trauma subgroups, look at similarities/differences between mental and actual flashbacks
Kroes et al. (2011) MRI with 28 PTSD p's using VBM
- flashbacks and their severity inversely related to the volume of the ventrolateral regions of the left temporal cortex and mid temporal gyrus --> areas are part of the ventral stream
= flashbacks associated with smaller structural volumes in the ventral stream
--> might reflect complementary volumetric changes to the decreased activations in the ventral stream seen in Whalley et al.
- Important that these relationships specifically related to flashbacks, not general symptoms which strengthens the comparison between this study and Whalley et al.
- Volume of right insula inversely related to flashbacks = unlike activations in Whalley et al. --> attribute to heterogeneity in trauma and symptoms? reflects hyper activation of S-rep areas = atrophy? reflects hyper activation of the insula potentially as a result of sensory re-living?
- Limitations: small sample, individuals with PTSD arising from a no. of sources but too small of a sample to look at subgroups, and problem with assuming causality
- Traumatic events alone have few long-lasting effects on memory and may even be forgotten if they are not salient to the person’s autobiographical self
- Memory disturbances are predominantly found in individuals with PTSD or other psychological disorders
- Flashbacks = perceptual/image-based rather than verbal, incorporate bodily reactions such as pain, involve automatic retrieval only, and reliving in present
- Hellawell & Brewin (2004) PTSD p's wrote detailed trauma narrative and indicated which words/sentences had spontaneously elicited flashbacks --> sections associated with flashbacks contained more perceptual details and mentions of motion, produced more interference with a subsequent visuospatial task than when writing nonflashback sections = they involve more perceptual processing resources
--> flashbacks are a form of AM distinct from ordinary memory (2 types=one that is automatically retrieved and one that is verbally retrieved)
- Important characteristic is the sense of “nowness”, (experienced as though occurring in the present) --> subjective lack of past temporal context decreases with successful treatments (Speckens et al. 2006).
- Trauma memories of individuals with PTSD more strongly characterized by this feature than their nontrauma memories --> distinguishes involuntary memories in PTSD from the involuntary memories reported by depressed patients/individuals who have experienced trauma but not developed PTSD (Birrer et al. 2007)
- Empirical studies: flashbacks appear to be a specific indicator of PTSD (Bryant et al., 2011), and the sense of nowness is predictive of the course of the disorder over and above the effects of initial symptom levels (Kleim et al. 2007).
1) Fill in gaps in partial C-reps with forgotten/ avoided information
e.g. detailed verbal or written narrative, prolonged exposure, focus on “hotspots”:
2) Making C-reps more retrievable
e.g. Eye Movement Densensitisation and
reprocessing, imaginal rescripting
- holding images in focal attention in the precuneus facilitates the transfer of successive parts of S-reps into more elaborated C-reps that can be integrated with existing autobiographical information
- it facilitates the association of these representations with one another by means of a pathway via the posterior parietal and retrosplenial cortices.
- the expression of S-reps can benefit from the contextualization provided by the hippocampus whereas C-reps can benefit from modification of their associations to autobiographical and semantic knowledge and from coming under greater inhibitory control by the PFC
- require PTSD patients to give an extremely detailed oral or written narrative of their traumatic event and to come into deliberate contact with trauma reminders, for example by revisiting the scene of the trauma.
- Some treatments, such as prolonged exposure (Foa & Rothbaum, 1998), involve repeating these procedures on numerous occasions until fear diminishes
Eye-movement desensitisation and reprocessing:
- p's retrieve and hold in focal attention an image of the worst moment of their trauma, together with any associated negative thoughts, while the therapist repeatedly introduces bilateral stimulation for periods of about 20s (called sets).
- Stimulation may take the form of requiring p's to track the therapist’s hand with their eyes backward and forward across the visual field, or of repeated taps on alternate hands, or of playing sounds that alternate between left and right.
(most common and empirically validated method is the visual tracking of the therapist’s hand)
- During and between each set, p's are instructed to allow images/thoughts to enter awareness or change their form, observing them but not attempting to influence the process --> facilitate memory contextualization.
- Directs patients to focus attention on traumatic moments that they may previously have avoided while simultaneously using a secondary task to reduce the intensity of the experienced images.
- Baddeley and Andrade (2000) and Postle (2006) have shown that carrying out eye movements selectively interferes with the visuospatial sketchpad and reduces the emotionality and vividness of images.
- p's focus on the contents of their intrusive image or memory and vividly construct an alternative, more positive outcome that they have previously generated and rehearsed with their therapist (Hackmann, 1998).
- Fantasies often include impossible elements (e.g. superhuman feats, supernatural beings, or impossible transformations of the physical world (Smucker & Dancu, 2005).
- rescripting involves first retrieving the C-rep corresponding to the intrusive memory or image, projecting it to the precuneus, and then, while it is being held in mind, reporting on the content of associated S-reps that are retrieved in consequence.
--> ensures that all relevant material in S-reps have the opportunity to be fully contextualized by association to a new C-rep.
--> A new and more elaborated C-rep is then constructed that blends this negative material with novel positive elements.
- If successful, the projection of this new C-rep to the precuneus will lead to the spontaneous retrieval of positive sensations and emotions from S-memory --> helping to consolidate it and make it more accessible.
- Can be used to support standard cognitive-behavioral interventions,e.g. cognitive challenging of negative beliefs, or as a stand-alone intervention.
- Promising effects, either alone or in combination with other interventions, in the treatment of the sequelae (pathological condition arising from a trauma) of child sexual abuse, BPD, bulimia , PTSD (Grunert et al. 2003), depression (Brewin et al., 2009), social phobia, and a variety of other disorders