The Impact of Trauma on Adult Sexual Assault Victims

PART III – How Trauma Affects Memory and Recall

People often assume and expect that we will be able to recollect major events in our lives with clear and unwavering accuracy and that this determines the “truth” of what happened.

“One of the most critical contributors to achieving just outcomes in [sexual assault] cases is eliciting the most complete and accurate information from the primary source of evidence – the complainant.” (Westera, Zydervelt, Kaladelfos, & Zajac, 2017, p. 15)

However, traumatic events such as sexual assaults, are encoded (converted) differently than more routine, everyday experiences in life. It is well known within the scientific and psychological communities that human memory and recall do not function like a tape recorder, faithfully recording events later to be recalled on command. Our memories are fallible and have gaps and inconsistencies. As a result, we recall and narrate traumatic events differently than routine events.

Memory and Recall: Some General Points

Memory is essentially the capacity for storing and retrieving information. Three processes are involved in memory: encoding, storage, and recall.

First we receive the information (e.g., from what we see, hear, and understand). Then we convert the information so it can be stored in various parts of the brain. There are three main ways in which information can be encoded: visual, acoustic and semantic. When encoding an event, we focus more attention on aspects that our brain appraises as important and less on those deemed insignificant.

This differential focus is what memory scientists refer to as central versus peripheral details.  Memory retrieval refers to “the access, selection, reactivation, or reconstruction of stored internal representations”. (Dudai, 2002) Additionally, over time memory works to edit information, and we lose memories, forget some details of memories we do retain, and modify aspects of other memories as the result of repeated retrievals.

Our brain-based memory systems have been sculpted to function adaptively. Memories of trauma are like normal memories in these respects, but they have important characteristics that make them much different from normal, everyday memories.

However, after being traumatized certain central events may be remembered forever and this is an adaptive outcome.  The brain has learned “this is important, remember this because it could later save your life.” To understand this more fully it is necessary to look at two key brain structures, the hippocampus and the amygdala.

The Hippocampus and the Amygdala: Encoding and Consolidating Memory

The hippocampus and the amygdala are two brain structures that encode memory. The hippocampus is responsible for putting experience into chronological order and into perspective; it is necessary for forming new explicit memories. Explicit memory is what we usually think of as memory. It is a “cognitive memory,” a memory we can remember in our thinking brain, or prefrontal cortex. 

For explicit memory, we need the hippocampus. This part of the brain is responsible for integrating the raw sensory data into a coherent picture, putting a time tag on it, and transferring it into long-term episodic memory, where it can be retrieved later. Over time, when memory is consolidated, its long-term storage is distributed in different parts of the neocortex. 

The amygdala, part of the limbic system, catalogues past sensory experiences (threats, anger) as implicit memories, memories that are unconscious but can affect thoughts and behaviours.  These memories are associated with intense arousal making them readily primed in order to quickly associate them with future situations that are stressful or threatening. This is a critical survival feature of implicit memory, enabling an instant response to danger.

Memory consolidation signifies the stabilization process of a newly formed long-term memory. McGaugh (2002) explains, that initially, unconsolidated memory is in a fragile state and can be disrupted by several types of interference, including behavioral, pharmacological, and electrical. Over time, the memory becomes resilient to these forms of interference through the process known as consolidation (McGaugh, 2000). 

Scientific information on the stabilization of memory through consolidation has significant implications for the timing of police interviews. A victim interviewed shortly after an assault, or while still very stressed or traumatized, will not be able to retrieve everything that’s been encoded into her brain. Two full sleep cycles may be necessary for the episodic memory circuitry to consolidate information that was encoded at the time of a trauma such as sexual assault. Researchers have found that processes occurring during both rapid eye movement (REM) and non-rapid eye movement (NREM) sleep also play critical roles in the consolidation of memories.  During memory consolidation, the brain reorganizes and integrates initially fragile memory traces into long-term storage. (McGaugh, 2000)

In many police services in the US and now in Canada, trauma informed police officers understand that it is best practice for a sexual assault investigator to conduct only a brief initial interview when a victim first reports a sexual assault. This should be followed by a fuller interview several days later when the victim has had time to sleep and consolidate her memories of the traumatic experience.  In fact, some police services maintain this same practice, of allowing for memory consolidation after two full sleep cycles before interviewing police officers who have been involved in a shooting.

How Threat and Highly Stressful Events Affect Memory

Normally, the amygdala neurons encode fear memory traces (or fragments) while the hippocampus learns about the context of the fear. But when faced with threatening experiences, this emotionally arousing information increases amygdala activity. That activity correlates with more deeply remembered memory traces in the amygdala.

Stress and fear heighten activation of the amygdala. This reinforces and intensifies traumatic memories while at the same time impairing hippocampal function, which is involved in episodic or explicit memory. Victims whose memories are not integrated into their hippocampus and cortical circuitry have implicit or limbic memory traces (or fragments). This happens because the amygdala activates the HPA axis, resulting in a flood of neurohormones that interfere with hippocampal learning. This is why, after a stressful situation, people have trouble remembering some specific details, and say things like, “It was all a blur.”

Implicit memory, also called procedural or sensorimotor memory, refers to behavioral knowledge of an experience without conscious recall. It is not a memory we can reflect on or think about. These memories are impossible to verbalize. They are often fragmented in time, and for the most part consist of primary sensory information (images, smells, sounds) that are linked to physiological fear symptoms. (Brewin, 2011)

Trauma and Memory

Cognitive models highlight the nature of the traumatic memory: fragmented, associated with intense arousal, readily primed and triggered, and poorly contextualized into memory. (Ehlers & Clark, 2000) As a result, memories of traumatic events such as a sexual assault can be fragmentary. It can be difficult for victims to recall many details of a sexual assault in a complete or linear way. 

Intensified Traumatic Memories: Flashbulb Memories and the Hippocampus in Overdrive Footnote 7

The effect of fear, threat or states of intense stress on memory can result in intensified memory recollection, or it can result in fragmented or impaired memories. Both are the result of the stress hormones released (the HPA axis) when the defence circuitry is activated.

Some elements of traumatic memories are more acutely remembered. The adrenal glands release adrenaline, which has been shown to help encode memories to the hippocampus more intensely.

A burst of adrenaline is thought to enhance memory storage of the events closer to the onset of a traumatic or highly stressful event. This strengthens memory pathways and creates what are referred to as “flashbulb memories.” (McGaugh, 2000)

It is not unusual for victims of sexual assault to have some full and vivid memories about the beginning of a sexual assault when the defence circuitry was first triggered and the initial burst of stress hormones were released. As well, central details or aspects of the experience that were of most significance may be intensely remembered.

Experiences with emotional significance are more likely to be consolidated into episodic memory and made available for intentional, conscious recollection than those with little or no emotional significance. The brain encodes what it pays attention to. During a threatening event, the brain focuses on what is central to survival so it does not focus on insignificant and peripheral details, so it does not encode them.

From Intensified to Fragmented Memories

When high levels of the stress hormone cortisol are secreted, along with adrenaline, the hippocampus super-encodes these intense early moments of the event. Following this, if the threat or fear continue, the hippocampus continues to be flooded with stress hormones and it is temporarily impaired and there may be minimal encoding. That is how the hippocampus goes from flashbulb mode to fragmentary mode.

For example, if during the 9/11 terrorist attacks an individual whose family member was working in an office at the world trade center turned on their television and witnessed the plane hitting the tower where their loved one worked, they would have a flashbulb or intensified memory of that terrible moment. But as events unfolded and they realized their loved one was not going to be able to escape, their brain would continue to be flooded with stress hormones and the events for the hours following the initial hit by the plane into the tower would be described as a blur.

When the hippocampus is in this fragmented mode, it encodes (converts) fragments of sensory memory without contextual details. As a result, a sexual assault victim might not recall the layout of the room where the rape happened. The hippocampus might not encode time-sequencing information because its functioning is altered during a traumatic event.

Not only can the hippocampus not integrate various systems of attention and memory, it also disrupts the storage of information. The hippocampus can disrupt memory encoding for conscious explicit memory when it is blocked or damaged by stress hormones or inhibited by intense amygdala activation. (Cozolino, 2017)

The amygdala is critically involved in calculating the emotional significance of events. When it perceives a threat, it creates emotional arousal. This is intended to alert us to pay attention and be ready to respond. The amygdala also has a selective effect on the particular stimuli we notice and encode. Fear focuses one’s attention on a few details at the expense of a lot of others. As a result, a victim of a sexual assault may not remember some of the details of the assault, for example, what colour of clothing the offender was wearing. Conversely, the central details of an assault or the parts of the experience that were the most disturbing are often well encoded and consolidated.

During states of fear (high arousal), the hippocampal and amygdala networks can become dissociated, resulting in a disconnection between the emotional memories of the amygdala and explicit hippocampal processing. Sensation, emotion, behaviour, and conscious awareness, which are usually integrated with one another, can be disconnected from their context in time and space. (Cozolino, 2017) As a result, few peripheral details, little or no context or time‐sequence information, and no words or narrative surrounding the memory may be recalled.

How Attention and Memory Affect Recall of Traumatic Events like Sexual Assault

Much of what is remembered of a traumatic or threatening event functions as if existing in separate islands of memory.

Information encoding and storage are impaired for aspects of the experiences that are not considered essential for survival or are of little emotional importance. This includes the sequence of events as well as peripheral details. This often results in a disorganized and incomplete narrative memory.

This is immensely important for how victims of trauma are interviewed. The primary emphasis of the sexual assault police interview should therefore be on the sensory, emotional memories that the victim has encoded and remembered rather than expecting the victim to give a narrative with a chronology.

Enhanced Traumatic Memory Coexists with Incomplete Memory

Some elements of traumatic memories are actually more acutely remembered than others. These are called enhanced memories. They are etched more deeply in our memories precisely because they are traumatic and overwhelming to us.

Victims often focus on some specific sensory details from the assault. For example, they often remember specific smells (the smell of body odour), but very few details of other aspects of what happened, for example, how long the assault lasted or the specific order in which some things happened. These are normal limitations of memory. They are caused by the stress and fear of the traumatic events and how the brain’s defence circuitry affects attention and memory consolidation. (Schwabe, 2016)

Some fragments of a traumatic experience, then, can seem like they are “burned into” memory. This is how they are recalled. This is normal and typical for how humans recall virtually any traumatic or terrifying event. For example, a person may claim that, “I’ll never forget!” a certain powerful memory of an experience, in reference to some particular aspect of it, which seems indelibly etched upon them. Yet they may have no memory of other peripheral details that were irrelevant to their survival at the time of the experience.

This is, in fact, what we all witnessed in the very high profile media attention surrounding Dr. Blasey Ford’s testimony at Brett Kavanaugh’s United States’ Senate hearing pertaining to his appointment to the Supreme Court in that country. Dr. Blasey Ford had some gaps in her memory of the night she describes being sexually assaulted by Kavanaugh. She was able to recall central details of what she experienced that night but was unable to recall some of the peripheral details, including how she got home from the party that night. These gaps in her memory became the subject of high profile attacks on her credibility, including by Republican Senators in a memo rife with inaccuracies written by prosecutor Rachel Mitchell, as well as attacks by others. However, these critics fail to understand that lack of recall of these kinds of peripheral details does not impugn the veracity of Dr. Ford’s account, or indeed the account of other sexual assault victims; instead it is consistent with the way in which traumatic memories are encoded.Footnote 8

These kinds of normal inconsistencies have been seized upon by defence lawyers, amplified to intersect with dominant and pernicious rape myths in our society, and used to undermine victims’ credibility in sexual assault trials. These are impermissible lines of reasoning in the Canadian criminal justice system.

Conclusion: Putting Advances in Understanding How Trauma and Memory Function to Work in the Criminal Justice System

Advances in cognitive neuroscience and neuroimaging have facilitated a much greater and deeper understanding of the neuroanatomy and neurophysiology of trauma and its impact on how we encode, and then later recall, traumatic events.

The science of memory and psychological trauma must be applied to interview approaches and techniques. The belief that inconsistent statements mean the victim is lying has created a focus on techniques that focus on lie detection. These approaches further stress the victim and often inhibit what memory the victim is able to recall.

This knowledge is of critical importance to sexual assault investigations: if a victim is interviewed in a stressful way – for example, if they are not treated with compassion, if their narrative is interrupted, if they receive only expressions of doubt about what they are reporting – they will not be able to recall potentially crucial information that is stored in the brain.

Memories that are consolidated are more stable and more resistant to interference (McGaugh, 2002). This means that consolidated memories would be more reliable and more consistently remembered and hence more useful for detailed victim statements taken by police.

These memories are not recalled in the same ways as other, more typical, life events.Footnote 9 In fact, memories associated with a traumatic experience are encoded in the brain differently than “normal” and more everyday memories. This is crucial information for the prosecution of sexual assault cases in the criminal justice system because sexual assaults are not normal events but ones that typically have profound neurobiological effects on brain, body and behaviour.

It is neither realistic, nor rational, to expect victims of sexual assault to recall all aspects of their traumatic experiences with detailed accuracy from start to finish. That is not how the brain works when the defence circuitry has kicked in. Understanding this is part of what a trauma-informed criminal justice system requires if justice is to be done and fair trials are to be conducted for the accused and for victims.