The Role of Memory in Trauma

 

Firstly, what is Memory?

(The following is taken from Daniel J. Siegel, The Developing Mind, 1999)

The neurons in our brain are formed into a neural network. Memories are not items stored in specific locations in the brain, ‘one memory in one location’. A ‘memory’ is constructed by the firing of a configuration of neuronal pathways which affects the probability of that configuration firing again in the future. The more it is fired, the more it is likely to fire, as protein molecules are laid down along that network, causing those pathways to get larger and stronger.

This is how learning occurs. Information is encoded and retrieved through the firing of the particular network. This is how the brain ‘remembers’. So chemical alterations strengthen connections between neurons (for short term encoding) and activate genes to create new connections for long term memory storage. Memory storage is the change in probability of activating a particular neural network pattern in the future. Retrieval is the actual activation of it, which will produce an experience in the mind that is similar but not identical to the profile activated in the past. (Siegel, 1999)

Hebb’s Law : “neurons that fire together, wire together.”

Repeated activations create ‘associations’ between different parts of the network, so that activity in one part facilitates activity in the other. [This is the neurobiological explanation behind the PTSD phenomenon of ‘being triggered’.]

ENGRAM

The initial impact of an experience creates an ‘engram’ of that event. It includes information that is recorded

  • semantically (in words),
  • factually,
  • autobiographically,
  • somatically (body sensation),
  • perceptually (visual images),
  • behaviourally and
  • emotionally (as feelings).

We can recall events in various ways. Semantic memory is the memory of facts, figures and information that we acquired through language. Episodic or autobiographical memory refers to memory of events (episodes) that happened to us personally. Procedural memory refers to the knowledge of how to do things (like ride a bike or type).

The ‘gist’ means that we know that we once went to a particular restaurant, but can’t actually remember it. ‘Specifics’ recalls the details.                

IMPLICIT & EXPLICIT MEMORY AND MENTAL MODELS

The brain constructs generalizations from experience, and these generalizations are called ‘mental models’. For example, learning and/or experience teaches us that crossing any road can be dangerous. We do not have to assess every road we come to beyond a quick glance, because we have a mental model to refer to regarding ‘crossing roads’. Until a child learns this, she has to be taught at every single crossing what the specific dangers are. Mental models allow us to assess situations more rapidly and decide what the next moment is likely to offer, what to expect. Life becomes familiar and able to be negotiated.

The brain is thus an ‘anticipation machine’, scanning the environment and trying to guess what comes next. Our memory, perception and emotional responses to the environment are not just produced from our individual history but are also genetically inherited from the evolutionary history of our species.

Implicit memory : consists of mental models which become automatic, as well as emotions, images and behaviours. Implicit memory is encoded early in life, driven mainly by emotional experience.   It is experienced as a present state-of-being, not as something being recalled. (This is important for an understanding of the traumatic memory recall of someone who has Posttraumatic Stress Disorder, as the recall is from the implicit system.)

Implicit memory can be thought of as connected to intuition. Animals act on intuition, as it is a more rapid response system than autobiographical memory. It is not surprising to find then, that implicit memory is stored in the lower, more primitive parts of the brain, in the limbic system and brain stem. Implicit memory is less available to the cognitive mind, is more automatic.

Explicit memory : facts, events, autobiographical consciousness.

♦ Mediated by the hippocampus, medial temporal lobe and orbitofrontal cortex.

♦ ‘Event memory’ can exist without a sense of self involved in the event. These are facts that can be assessed as true or false.

♦ ‘Autobiographical memory’ (known as autonoesis or self-knowing), involves the frontal cortex. ‘Mental time travel’ is the recollection of self in past events, lived present and projections into an imagined future.

♦ The hippocampus helps to construct a mental map of events happening in space, and frontal lobes construct a sense of ourself existing across time. Thus we have a 4-dimentional sense of self existing in space and time.

 

MEMORY ENCODINGhippocampus

Memory is encoded in the left hemisphere. Hippocampal organ stretches across both hemispheres and encodes short (5 to 10 seconds) and long-term memory (1 to 3 days). Permanent explicit memory is encoded in the neocortex after consolidation (sorting of details, sense-making processes, final ‘decision’ about what elements go into permanent memory).

Note:  The current belief is that memory is encoded initially in the hippocampus and only encoded in the cortex after a sorting and consolidation process that is thought to happen during REM sleep. This view is being challenged by recent research with mice that suggests that memory of an event (for example) is encoded in both the hippocampus AND the cortex at the same time, with the cortically located memory not being available to recollection for an (unspecified) period of time.  The report of this research is reproduced here.

 Explicit memory (semantic/episodic)  Implicit memory 
Requires focused attention In the context of trauma:

 

Divided attention (eg.dissociation)

Experienced as:

 

I am recalling something

 Experienced as:

 

I am experiencing something -no sense of recalling past experience

Hippocampus encodes context-dependent information into the explicit memory network.
This is why emotional or environmental cues can trigger memory.Context-dependent : emotional, sensory and environmental elements that were present at the event.
The implicit memory system is not in the frontal cortex, is separate from the explicit system and mediated by the more primitive parts of the brain. This is why people with amnesia can still remember how to do things, learn new skills and have emotional associations.

 

Divided attention experiment: 

Earphones on left and right ears.   List of zoo animals read into left ear, list of flowers read into right. Participants instructed to give focal attention to left ear, zoo animals.

Most will have good memory of zoo animals, most will have little memory of flowers.

BUT, when asked to fill in the spaces in a partially spelled word, ie, R – – E, they are more likely to put in ROSE. The subjects have encoded the list of flowers implicity, and the brain is ‘primed’ to bring up a flower when cued. Subjects have no sense that they are recalling the word, or that what they are writing is something they experienced.

Without focal attention, items are not encoded explicity.

 

MEMORY RETRIEVAL 

Memory is retrieved from the right hemisphere.

Cues can activate both explicit and implicit memory simultaneously. Recollections will often involve explicit elements associated with their implicit context-dependent counterparts.

SO, a client is telling you about her relationship with her alcoholic father. Suddenly she is overwhelmed with feeling, tears and shaking. She may compose herself and continue. What has happened is that she has been flooded with implicit elements of her childhood story.

In composing herself, she pushed these implicit elements back down, to some extent dissociating from them, but will probably feel shaken for some time after.

Associational networks mediated by the orbitofrontal cortex:

Emotional states                                              Consciousness
Bodily responses                                             Identity
Reasoning                                                       Memory
Memory retrieval                                             Perception
Perceptual biases                                            Social cognition
Appraisal of stimuli                                          Regulation of emotion

 

The blockage of integrative circuits may separate these mental processes from one another and give rise to states of incoherence, disorientation, amnesia and other dissociative processes.

 

The Role of Memory in Traumatisation

It is the failure of the information processing system to construct a coherent autobiographical narrative of the event that causes it to become traumatic. It is the encoding of the event into implicit, rather than explicit memory that prevents it from being successfully integrated into the person’s sense of personal history.

In the heat of a catastrophic event, one that is potentially traumatizing, a participant or observer’s nervous system (the emergency stress-response system) goes into emergency mode. This is discussed under the Trauma tab, “The Neurobiology of Trauma”. Under extreme stress, a person tends to dissociate, which means that part of their attention or consciousness is focussed on the event, but some of it is focussed on a ‘safety’ object, something that helps them contain their natural panic and fear. It is thought that successful consolidation of long-term memory requires focussed attention. Without this, some or most of the memory of the event will be stored in the implicit memory system – as feelings, emotions, bodily sensations, sensory elements and automatic beliefs, as has been described in the previous section.

The important element here for the understanding of traumatisation, is that memory is inextricably entwined with self knowledge, autobiographical narratives, emotional responses and states of consciousness. These functions are organised and linked together by the circuits within the frontal cortex. All of these elements are affected and altered by the experience of traumatisation. This is discussed further under ‘Dissociation’.

Prefrontal_cortex

 

More on Trauma

Trauma

What is Trauma?

The Neurobiology of Psychological Trauma

Dissociation

An Evolutionary Model of Response to Danger

The Brain’s “Information Processing System”

Further Resources and Reading (Trauma)

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