Traumatic Memories A Neuroscience Perspective

Homayoun Shahri, PhD, MA, LMFT

http://www.ravonkavi.comHomayoun.shahri@ravonkavi.com

Trauma and Traumatic Memories

Shock Trauma vs Developmental Trauma.

Shock trauma is sudden, massive, and may be chronic. It affects individuals in their core, and may alter the functioning of the brain including the frontal cortex, limbic system, parietal lobe, insula cortex, and visual cortex, etc.

Developmental trauma, is usually chronic, happens during developmental stages, and is mostly due to non-optimality of caretakers responses to the developing child.

Developmental trauma can and does affect brain functioning but generally not in the same way as shock trauma.

Developmental trauma is also referred to as complex trauma.

At the core of understanding trauma and healing trauma, is the nature of traumatic memories and their activation.

Neurons

At the core of the brain are the neurons.

There are about 100 billion neurons in our brain, and each neuron can have thousands of connections with other neurons.

Neurons communicate via their axons (transmitters) and dendrites (receivers).

A neuron can have thousands of dendrites, thus receiving input from thousands of other neurons.

Neurons however, usually have one axon, but axons can have many branches

Neurons

Synapses

The junction where an axon meets a dendrite is called a synapse.

The neurons transmit information by their axon to other neurons through synaptic space.

When an electrical signal reaches the end of the axon it releases neurotransmitters contained in Vesicles.

These neurotransmitters travel through the synaptic space and bind to dendrites of other neurons, resulting in electro-chemical changes in the body of receiving neurons.

There are two general types of neurotransmittersInhibitory and excitatory neurotransmitters.

Excitatory neurotransmitters stimulate the brain (increase the potential buildup in the receiving neuron)

Inhibitory neurons calm the brain (reduce the probability of potential buildup in the receiving neuron).

Synapses

Neurons and Electro-Chemical Reactions

The main inhibitory and excitatory neurotransmitters in the brain are Gaba (Gamma-Amino Butyric Acid), and Glutamate respectively.

Other neurotransmitters also play a significant role in brain information processing and memory.

When the receptors on the receiving dendrites bond with the neurotransmitters, and electro-chemical change inside the neuronal cell takes place, this results in increase of the internal potential of the neuron from a resting voltage of -70 mV to possibly a voltage of +40mV. At this point the charge rapidly decreases to -90 mV, which results in release of neurotransmitters into the synaptic space of the receiving neuron through its axon.

This event is called action potential and the rise and fall of potential is called a spike.

Action Potentials - Spikes

Spike Trains

A neuron usually releases a sequence of spikes called a spike train, or a train of action potentials.

Neurons do not function in isolation.

The axon of one neuron may form synapses with dendrites of many other neurons.

Many neurons may fire action potentials at the same time.

The question is, what happens when many neurons are involved in generating action potentials?

Spike Trains

Neuronal Firing

Reconstruction of image with one ganglion cell of salamander using relative latency and spike count

Mathematics of Synaptic Firings

What is the mathematics of synapses? (Joseph LeDoux)

Exuberance that is more synapses are made than are preserved.

Use that is the synapses that are preserved are the ones that are active.

Subtraction that the synaptic connections that are not used are destroyed.

This points to synaptic plasticity.

It means the brain is constantly in the process of rewiring itself, thus forming new synapses, and destroying others.

Neural Networks

Neural networks and memory are associative.

Associative memory is defined as the ability to learn and remember the relationship between unrelated items.

In 1949, Donald Hebb suggested that if the axon of neuron A is close enough to the dendrite of neuron B to excite it and result in action potential, and if the process occurs repeatedly and consistently, then the connection between neurons A and B will be strengthened, and will result in higher likelihood that neuron B fires an action potential in response to neuron A.

Hebbian Axiom: Neurons that fire together wire together.

Neuroscience of Memory (A microscopic view)

Memories are represented by associative neural networks which are separate but linked together.

For associative networks to form, constituent networks must have reached a certain degree of activation.

This activation is dependent on the constituent components of memory, as well as the weight of each component.

The weight of the components is dependent on the cues that were present during the learning process, and are also present during recall.

These cues in many cases are emotions associated with the components of memory.

The cues in this case may be signals from brain and the body (emotions) that indicate that we may be in the same emotional state as during the time of formation of memory.

Neuroscience of Memory (Cont)

It is also very important to emphasize that memories are a reconstruction of events at the time of recall.

Our emotional state can influence the way the recalled memory is remembered.

The converse is also true in that memories are recalled and remembered best when one is in the same situation or emotional state.

Emotions may affect the recall of certain aspects of memory more than others.

In general, the memory of the more emotionally significant aspects of an experience is remembered better than the more emotionally benign aspects of memory.

Neuronal Firings and Emotional Significance

Look at checkered patterns.

Which do you notice?

Thalamus and Amygdala

All the sensory nerves (except for olfactory nerves) end up in the thalamus and are then relayed to various parts of the brain including Amygdala.

The thalamus (which has two halves) can be thought of as brains switchboard or information hub.

The amygdala is an almond size structure (one on each side of the brain, deep within the limbic system), which is responsible for appraisal of stimuli and evaluation of emotional significance of the stimuli.

Amygdala has also been named The Smoke Detector of the Brain.

Amygdala Brains Smoke Detector

The Low Road and the High Road

High road runs through the hippocampus and anterior cingulate to the prefrontal cortex, and then is sent to Amygdala.

Low road runs directly from Sensory Thalamus to Amygdala.

It takes 30 ~ 50 mSec for information to travel Amygdala via the low road.

It takes 400 ~ 500 mSec for information to travel to Amygdala via the high road.

The Low Road and the High Road

Memory A macroscopic view

Memory, in its most general sense, can be defined as what we consciously recall from past events.

But memory is more than what we consciously recall from the past.

If a certain neural pattern has been activated in the past (in response to external or internal stimuli) then the probability of activating a similar pattern in the future is enhanced. This is how we remember and learn from the past.

The increased probability of firing a similar pattern is how the neural network remembers.

Memory storage is the change in probability of activating a particular neural network pattern in the future.

Memory (Cont)

Memories can be categorized in two broad categories: implicit and explicit.

Implicit (procedural) memory can exist early in development and can be present at birth.

Implicit memory is not subject to recall whether of self or of time (timeless).

Emotional, somatosensory, and perceptual memories can be encoded as implicit memories.

Generally attention is not required for encoding of implicit memories.

Recall of implicit memories is independent of the hippocampus and medial temporal lobes, and thus not under conscious control.

Memory (Cont)

Encoding of explicit (declarative) memories begins near the second year of life, and includes semantic (factual), and episodic (autobiographical) memories.

Explicit memories require conscious awareness for encoding.

Explicit memories involve a subjective sense of recall and are not timeless, that is there is the notion of time in encoding of explicit memories.

The hippocampus, and the temporal lobes and cortices are involved in processing and encoding of explicit memories.

Memory (Cont)

Our brain generally does not encode and save every experience as explicit memory.

It seems that the more emotionally intense an experience is, the higher the probability of its encoding and recall. The event is simply labeled as important (by the amygdalae).

Events that are filled with fear, terror or are just overwhelming may not be encoded by the hippocampus.

Several factors such as amygdala discharge and various neuroendocrines including noradrenaline and corticosteroids may inhibit the functioning of the hippocampus, thus blocking the encoding of the event and later recall.

Memory (Cont)

Fear or terror filled events may be stored in implicit memory as fragments, while explicit memory is impaired.

When implicit memory is reactivated, it is not associated with a sense of time, place, and sense of self in time, nor is there a sense that something is being recalled. Implicit memory stores emotional dynamics of events, and not their contents.

The brain can have implicit memory (mainly stored in the limbic system) from very early in an infant's life (even prenatally).

It is only after roughly the second year of life that the hippocampus is developed enough to encode explicit memory.

Memory and Stress

Stress also mediates encoding and storing of explicit memory. Small amounts of stress generally do not have a significant effect on encoding events into memory.

Moderate amounts of stress help to encode events into memory for later recall.

Large amounts of stress impair memory encoding and recall.

Chronic Stress affects the size and functioning of the hippocampus, which mediates encoding of explicit memory.

Chronic elevated levels of the stress hormone cortisol results in atrophy of the hippocampus.

Traumatic Memories

In shock trauma, the signals from afferent neurons (sensory neurons) may not fully reach the cortex to be processed.

Hippocampus cannot categorize, organize, and encode the memories.

These memories may not be recalled as a complete whole, but only are recalled as fragments and tend to be associated with sensory inputs, and certain body states, which may include sounds, imagery, touch, and certain body positions.

Traumatic Memories (Cont)

Emotional aspects of the traumatic memories are stored as implicit memories in the limbic system.

There is a splitting off or dissociation of contents of the painful experiences from the emotional aspects and dynamics of the experiences.

The painful contents are repressed while the emotional dynamics are retained as implicit memories.

Traumatic memories may be repressed, dissociated or both.

Repression vs Dissociation

Repression is both motivated and defensive.

Dissociation does not have to be motivated or psychologically defensive.

Repression refers to formulated experience, and dissociation generally refers to unformulated experience.

Repression usually refers to a piece of information that was accessible at one time but not at another.

Dissociation usually refers to divisions of experience in which the parts are side by side, contrasting, and may be concurrent in time. Dissociation refers to states and systems of states, which are often mutually exclusive.

Dissociated memories are especially context-dependent.

Recall of Traumatic Memories

The recall of (degraded) past memories recovers some parts of these memories but may further augment these memories for meaning (elaborative repression), in an effort to reduce the uncertainty, and increase predictability in order to reduce arousal.

In dissociation this same process may not occur, as these memories are highly state dependent and typically are not amenable to augmentation the way repressed memories may be.

This is partially due to the nature of the dissociated memories that overwhelm various neuronal circuits and block the normal processing of these memories.

Gluing of Dissociated Memories and Healing

It may still be possible to glue the dissociated memories together to make some sense of them, and to reduce arousal.

For this gluing of dissociated memories to be possible, clients must be able to tolerate high arousal and not be overwhelmed, while the narrative is being reconstructed.

It is understood that the presence of an empathic, supportive, and attuned therapist is a crucial stem in this process.

This form of client-therapist connection allows clients to make left hemisphere centric sense of their right hemisphere representations, resulting in the capacity to regulate strong emotional states.

The presence of an empathically attuned therapist may keep the clients arousal within a tolerable level, causing the integration of traumatic memories.

Case Studies

My own experiences

Case of Elizabeth

Case of Jane

In both cases, we were able to glue the fragmented and dissociated memories of the abuse with new memories that were empowering, reduced their arousal and lowered the activation of their amygdalae.

It might be possible to trigger synaptic plasticity and reconsolidation of aversive memory in the lateral amygdala (LA) by introducing new information at the time of recall and reactivation (Daz-Mataix, Ruiz Martinez, Schafe, LeDoux, & Doyre, 2013).