PTSD as a mental disorder

PTSD is a mental disorder that can develop after severely distressing events such as war, sexual assault or witnessing a death, resulting in a traumatic experience that damages the mind (psychological trauma) by impacting the brain (physiological trauma).Footnote ⁵ People with PTSD persistently re-experience the traumatic experience via intrusive thoughts, nightmares, “flashbacks”, and emotional and physical distress. They suffer negative thoughts and feelings, avoid trauma-related reminders and experience hyper-arousal symptoms such as irritability and difficulties concentrating or sleeping. In response to trauma-related stimuli they often experience dissociative symptoms such as depersonalization (feeling as if “this is not happening to me”) or derealization (“things are not real”).Footnote ⁶ Patients often report feeling as if the traumatic event is happening in “real time” instead of in the past, which evokes a sense of current threat.

Beyond psychological symptoms, people with PTSD often experience interpersonal, psychosocial and health problems. For example, they are at an increased risk of cardiovascular disease, drug addiction, intimate partner aggression, divorce, job loss and confrontations with the legal system.Footnote ⁷ The economic burden of PTSD to society during the 1990s was estimated to be $42.3 billion per year,Footnote ⁸ which will have likely risen by now due to the generally increasing medical costs.

Prevalence of PTSD

Exposure to psychological trauma is a common occurrence.Footnote ⁹ An estimated 50% of men and 60% of women experience at least one trauma during their lifetime.Footnote ¹⁰ Around 8% of these men and 20% of these women develop PTSD.Footnote ¹¹ In a given year, 8% of the general population has a current diagnosis of PTSD.Footnote ¹² Extrapolating, this means that ~26 million people in the United States, ~41 million in the European Union and ~110 million in China currently suffer from PTSD; numbers for developing countries might be even higher, as exposure to stressors may be greater.Footnote ¹³

The prevalence of PTSD amongst soldiers is higher than in the general population. Of the roughly 2 million US soldiers who served during Operations Iraqi Freedom, Enduring Freedom, Desert Shield and Desert Storm, 10–20%, or some 200,000–400,000, experienced PTSD in a given year.Footnote ¹⁴ It is estimated that 30% of the approximately 3.4 million US soldiers (that is, roughly 1 million) who served in Vietnam will experience PTSD in their lifetime.Footnote ¹⁵ Amongst civilians in armed conflict situations, the prevalence of PTSD is also around 30%.Footnote ¹⁶ Given the nature of contemporary conflicts, however, many more civilians than soldiers experience war and thus end up suffering from PTSD.Footnote ¹⁷

PTSD and memory

While a number of psychological theories on PTSD have been put forward, memory plays a critical role in all of them.Footnote ¹⁸ Indeed, PTSD might even be considered a memory disorder.Footnote ¹⁹

The defining onset of PTSD is a traumatic experience that results in the formation of a traumatic memory. The severity and the perceived threat of the traumatic experience predict PTSD severity,Footnote ²⁰ and are also factors known to strengthen memory formation.Footnote ²¹ Moreover, PTSD may develop because the traumatic experience shatters our learned assumptions and beliefs about the safety of our world.Footnote ²²

PTSD is characterized by intrusive memories. The content of intrusive memories often includes trivial stimuli or situations that preceded the traumatic event.Footnote ²³ For example, a war veteran may have intrusive memories of rustling leaves that were seen or heard prior to the emergence of enemy soldiers from the jungle. Such memories may serve as “warning signals” that are later interpreted as signals of impeding danger and thus evoke a sense of current threat. As such, intrusive memories are learned predictors of danger that come to evoke defensive responses, avoidance behaviours and involuntary retrieval of thoughts, feelings and memories of the traumatic event.

People with PTSD involuntarily re-experience intrusive memories as if happening in “real time”, but often have difficulty purposefully recollecting the trauma memory.Footnote ²⁴ They tend to recall disjointed fragments of the traumatic event; recall is often not chronological but jumps back and forth in time between events, and unlike in ordinary memory retrieval, people often get “stuck” or “hung up” on particular details and feelings. As such, traumatic memories in PTSD may be processed differently from ordinary emotional memories and may be qualitatively different and possibly stored differently in the brain.Footnote ²⁵

Many who experience psychological trauma will initially develop PTSD-like symptoms, but most will learn to overcome these symptoms over time.Footnote ²⁶ Only a portion of people who experience trauma will not learn to control traumatic symptoms and will develop PTSD.Footnote ²⁷ Thus, disturbances in learning to control emotional responses and memory for situations of safety also contribute to PTSD.

Effects of trauma on emotional memory systems in the brain

People with PTSD exhibit enhanced responses to aversive stimuli indicating hypersensitivity of the nervous system to stress, and hyper-reactivity to trauma-related stimuli. PTSD is associated with abnormalities in neurotransmitters (chemicals that allow communication between brain cells) and stress hormones, such as noradrenaline, serotonin and cortisol, as well as brain structure and function in regions involved in emotional memory and emotion regulation.Footnote ²⁸ Brain abnormalities have been observed in the amygdala (important for learned threat responses), ventromedial prefrontal cortex (critical to inhibition of threat responses) and hippocampus (important for behavioural inhibition and memory for episodic events). This may explain the hyper-arousal and hyper-reactivity symptoms, inability to regulate fear, fragmentation of memory for the traumatic event, and re-experiencing of symptoms in PTSD. These abnormalities may constitute vulnerability factors, or may be acquired following trauma exposure, or may interact to contribute to PTSD.

What is memory?

Memory is the capacity for persistence of information over time. For the purposes of cognitive neuroscience, memory can be defined as an internal representation of an experience captured in a physiological change in the brain, enabling the expression of the earlier experience in thought or behaviour.Footnote ³⁶ This definition contains two components: the expression of memory in thought or behaviour, and its neural underpinning. The latter component is called an “engram” or “memory trace”.Footnote ³⁷ This also means that with anything you learn, you are changing your brain.

Different “types” of memory

Different behaviours and thoughts are supported by distinct neural systems that all have the capacity for memory.Footnote ³⁸ As a result, psychologists have distinguished between different types of memories.Footnote ³⁹

Two memory types that contribute to PTSD and that we will mainly discuss here are conditioned memories and episodic memories.Footnote ⁴⁰ Aversive conditioned memories can be formed via Pavlovian threat conditioning where pairing a stimulus (such as a sound) with an aversive outcome (such as pain) can come to evoke defensive responses (for example, changes in heart rate), indicating the formation of an association between the stimulus and the outcome in memory.Footnote ⁴¹ Such conditioned threat memories may contribute to the hyper-arousal and re-experiencing of symptoms evoked by “warning signals” in PTSD.Footnote ⁴² Episodic memory involves memories of particular experiences that include associations between who, what, where, when and whyFootnote ⁴³ – for instance, recalling “in our mind's eye” a particularly distressing war experience. Episodic memories play a role in the re-experiencing of autobiographical events of the traumatic experience in PTSD. For example, “flashbacks” involve the reliving of the traumatic episode as if happening in real time. Furthermore, episodic memory of the traumatic experience is often fragmented in PTSD, and in extreme cases people may have no episodic memory of the traumatic event at all (amnesia).

Hence, different “types” of memory contribute to distinct symptoms in PTSD. But how are these memories formed, and why are they so difficult to control or modify?

Neuroscience of memory formation

Experiences create patterns of neural activation in the brain via our senses. The formation of a memory of an experience involves the strengthening of connections between brain cells activated by an experience and requires neurotransmitter signalling, gene transcription and protein synthesis. Drugs or other interventions administered right before or after learning – that is, at the moment of acquisition of information of an experience – can impair memory.Footnote ⁴⁴ However, the same interventions administered hours after learning no longer have an effect on memory. This has led to the standard view on memory, which suggests that memories are initially labile (meaning they are sensitive to modification by interventions) but stabilize over time during a period of “consolidation”, after which they are stable and can no longer be modified.Footnote ⁴⁵ Neurotransmitters and hormones that are released during emotional experiences, such as noradrenaline and cortisol, can strengthen consolidation and as such result in an emotional memory enhancement.Footnote ⁴⁶ At the same time, this implies that immediately before and after a traumatic experience, there may be a brief window of opportunity to prevent a trauma memory from becoming permanently stored or to minimize its emotional enhancement.Footnote ⁴⁷

Extinction and the return of symptoms

Patients often come into a therapist's office long after a trauma memory has formed and been consolidated. The often-observed return of PTSD symptoms even after initially successful psychotherapy can be explained because treatment (particularly exposure treatment) is based on principles of extinction learning of Pavlovian conditioning.Footnote ⁴⁸

During extinction training, a threatening stimulus is repeatedly presented without an aversive outcome so that over time the person will stop displaying threat-related defensive responses. However, extinction learning does not modify the original threat memory. It rather forms a novel safety memory in the ventromedial prefrontal cortex that inhibits the expression of threat responses in the amygdala, and this can give way to the return of threat responses with the passage of time, changes in context or increases in arousal.Footnote ⁴⁹

From an evolutionary perspective it makes sense not to overwrite a conditioned threat memory, as the threat memory is adaptive and protects us from danger. However, the unfortunate result is that psychotherapy most likely also does not alter the original trauma memory but forms a novel safety memory,Footnote ⁵⁰ even though trauma memory is clearly maladaptive/harmful in PTSD. This leaves the risk of the return of symptoms even after initially successful treatment.

Flexibility of memories

Notwithstanding the stabilization and persistence of memories, it is known that memories, particularly episodic memories, can be flexible.Footnote ⁵¹ Most of what we initially remember, we forget within twenty-four hours. What we still remember after twenty-four hours, we forget at a much slower rate.Footnote ⁵² When witnessing distressing events such as the Challenger Space Shuttle explosion or 9/11, we are often very sure about the accuracy of our episodic memories, but in fact we accurately remember only around 30%.Footnote ⁵³ Furthermore, with a bit of suggestion, it is possible to make people remember things that never happened, like being lost in a mall as a child.Footnote ⁵⁴

We thus forget most of what we initially remember, and our memories can be highly inaccurate or even completely false. This flexibility of episodic memory is adaptive, as it helps us to survive. Our environments continuously change, and forgetting may allow us to get rid of outdated and unimportant information and keep our memory “fresh”. At the same time, updating of episodic memories through new experiences and integration of memory from different experiences help us to better describe regularities of our environment. What is still unclear is whether the memory flexibility described here results from a modification of the original memory or confusion between different memories at the time of retrieval. Regardless, when discussing the ethical, legal and social implications of MMTs, it is critical to realize that memories are not a veridical reflection of the past but serve to support adaptive responses and decision-making in the future.

Memory reconsolidation

As discussed above, the classical view on memory suggests that memories are initially labile but stabilize over time during a period of consolidation, after which they remain essentially unchanged.Footnote ⁵⁵ Hence, consolidation provides a brief time window after learning to interfere with memory formation and potentially for prophylactic use of MMTs to prevent the development of PTSD. But the standard view on memory indicates that once memory is consolidated, MMTs would no longer be able to prevent PTSD. Contemporary neuroscience, however, has challenged the classical view on memory and suggests that it is possible for MMTs to modify consolidated memories.Footnote ⁵⁶ We will first discuss laboratory studies on modification of consolidated memories, and will then turn to clinical studies.

In a seminal study, Karim Nader and colleagues used rats to show that a brief reminder can reactivate a consolidated threat-conditioned memory and temporarily return the memory to a labile state requiring re-stabilization processes (such as protein synthesis), referred to as reconsolidation.Footnote ⁵⁷ It was found that disrupting reconsolidation processes by blocking protein synthesis can result in the loss of the conditioned threat responses and prevent their return.Footnote ⁵⁸ Note that Nader and colleagues purposefully do not call this memory erasure; as such a null hypothesis is scientifically impossible to confirm. In addition, we believe we should refrain from using the term “erasure”, as such terminology may spark unnecessary negative sentiment among the public.

To disrupt reconsolidation, Nader and colleagues injected a toxic protein-synthesis inhibitor, which is clearly not safe for use in humans, into the brains of rats. Subsequent laboratory experiments showed that the administration of noradrenaline antagonists (or “beta-blockers”, such as propranolol) could also disrupt reactivated memories and prevent the return of threat-conditioned responses in rodents and humans.Footnote ⁵⁹ Note that the disruption of memory by interventions such as beta-blockers only occurs under specific circumstances, namely, when memory is reactivated by a brief reminder and when the intervention is administered within a short time period after the reminder – that is, during the reconsolidation window. Furthermore, behavioural interventions may also impair reconsolidation: reactivating a conditioned threat memory to return the memory to a labile state and then administering extinction training during the reconsolidation window (reactivation–extinction paradigm) can also prevent the return of conditioned threat responses.Footnote ⁶⁰ Here the idea is that when memory is returned to a labile state, extinction can overwrite or update the original threat memory and thus negate the formation of a separate safety memory. Hence, the reactivation–extinction paradigm suggests that existing exposure treatments could be optimized by a minor change in procedures. Collectively, these laboratory experiments suggest that pharmacological and behavioural interventions, such as the use of beta-blockers or reactivation–extinction training, can disturb reconsolidation of reactivated threat-conditioned memories (e.g. memory for tone–shock associations) resulting in the loss of the expected reaction to a learned threat.

Interestingly, initial laboratory studies in humans indicated that reconsolidation interventions (both beta-blockers and behavioural interventions) specifically disrupted threat-conditioned defensive responses (e.g. sweating or startle responses) but left intact participants’ ability to explicitly recall the threatening experience to mind.Footnote ⁶¹ This has led to the suggestion that reconsolidation interventions affect only the “emotional” component of memory and preserve episodic memory.Footnote ⁶² However, subsequent studies indicate that reconsolidation interventions with beta-blockers and behavioural manipulations can diminish the emotional enhancement of episodic memory and that electrical brain stimulation can even fully eradicate specific episodic memories in humans.Footnote ⁶³ For example, in one study people who received electroconvulsive treatment (ECT) for unipolar depression learned two slide-show stories a week prior to treatment.Footnote ⁶⁴ Right before ECT, the participants were briefly reminded of one of the two stories to reactivate memory for this specific story. One day after the reminder and ECT, people could explicitly remember the story that they were not reminded of but could no longer remember the story of which they had been reminded. Thus, reconsolidation interventions can modify specific reactivated conditioned memories as well as episodic memories.

That said, reconsolidation interventions do not cause general memory impairments – meaning they do not impair all memories that we have.Footnote ⁶⁵ Only the specific memory that is reactivated and returned to a labile state can be modified.

From a clinical perspective, there are a number of limitations to reconsolidation interventions. First, evidence for reconsolidation has been obtained across many experimental paradigms and species, but not all studies have yielded positive results.Footnote ⁶⁶ Second, older memories, especially episodic memories, appear less sensitive to reconsolidation interventions.Footnote ⁶⁷ Third, much is still unknown about the conditions under which memories do and do not return to a labile state and can be modified. Fourth, if memory is reactivated but no intervention is administered or if interventions fail, reconsolidation strengthens memory. Hence, the opportunity to use reconsolidation-intervention techniques to treat patients who often have had traumatic memories for many years may be limited and, if interventions fail, reconsolidation may inadvertently strengthen trauma memories.Footnote ⁶⁸ Much research is still needed to translate this laboratory research into effective clinical applications.

Reactivating a memory can provide an opportunity for interventions to steer the reconsolidation of a specific maladaptive memory in a particular direction and potentially treat stress and anxiety disorders, including PTSD. Importantly, reconsolidation interventions would require only minor changes to existing psychotherapeutic behavioural procedures (for example, adding a brief memory reactivation prior to standard exposure treatment) or would involve a precise combination of psychotherapy and administration of a single dose of medication.

Clinical trials of memory modification technology

Based on laboratory experiments, several clinical trials have investigated the potential to use MMTs to prevent the formation of trauma memory, enhance exposure treatment, or impair reconsolidation of trauma memory to treat patients.

The administration of a beta-blocker to people admitted to an emergency department after a traumatic experience reduced threat responses to trauma reminders and PTSD symptoms one month later.Footnote ⁶⁹ Thus, beta-blockers may impair the consolidation of trauma memory and prevent the development of PTSD. However, the usefulness of this approach is limited, as the treatment needs to take place right after the traumatic experience to be effective, whereas most people with PTSD do not seek treatment until months after the trauma.

Another approach has been to improve exposure treatment by enhancing extinction learning – that is, by pharmacologically strengthening the formation of the safety memory that comes to inhibit threat responses. The administration of D-cycloserine (a drug that stimulates NMDA receptors, which are critical for the formation of new memories) can strengthen extinction learning, and its application prior to exposure treatment can improve treatment outcomes in patients with anxiety disorders.Footnote ⁷⁰ However, the problem is that the medication needs to be given before treatment, when the outcome of the treatment cannot yet be known: if exposure treatment ends up being successful, the medication strengthens the formation of a safety memory, but if exposure treatment ends up being unsuccessful, the medication can inadvertently strengthen the trauma memory itself.

The advantage of reconsolidation interventions is that they theoretically allow for the modification of specific memories at any time after learning and that the intervention can be applied after controlled memory reactivation. Initial clinical trials found that targeting reconsolidation of trauma memories with beta-blockers in PTSD patients can subsequently reduce threat responses to trauma reminders and reduce PTSD symptoms.Footnote ⁷¹ However, there are limitations to these studies,Footnote ⁷² and subsequent studies have failed to replicate them.Footnote ⁷³ The effectiveness of a beta-blocker reconsolidation intervention to treat PTSD thus appears limited. Note that PTSD patients are haunted by intrusive emotional episodic memoriesFootnote ⁷⁴ that they have often had for many years, and these may be particularly difficult to modify, as explained above. In that regard it is worth noting that targeting reconsolidation to treat specific phobias, which mainly involve conditioned responses, may be more effective.Footnote ⁷⁵

A series of interesting studies has attempted to disturb intrusive emotional episodic memories by using the computer game Tetris.Footnote ⁷⁶ In a small clinical trial, having patients who entered the emergency department play Tetris was found to reduce intrusions, and there was some evidence for a reduction in PTSD symptoms.Footnote ⁷⁷ The idea is that playing a visual-cognitive game like Tetris competes for the same limited neurocognitive resources that are necessary for the formation of emotional episodic memories and will thus disturb memory formation and prevent intrusions. A laboratory study reported that playing Tetris following memory reactivation can reduce intrusions in healthy participants (those who do not have PTSD or other psychiatric problems).Footnote ⁷⁸ It would be interesting to see whether a Tetris reconsolidation intervention could reduce PTSD symptoms in a clinical trial.

In sum, clinical trials have shown that MMTs may prevent the formation of traumatic memories, can enhance exposure treatment, and may disrupt reconsolidation of consolidated memories. However, the efficacy of clinical translations has so far been limited, potentially because it is unclear how to optimally target trauma memories or because not all types of memory may be equally sensitive to MMTs.Footnote ⁷⁹

Safety, effectiveness and equitable access

MMTs inevitably raise questions that pertain to all new medications or therapeutic devices. First, is the intervention safe – is it relatively free of serious adverse side effects? Second, is the intervention effective – does it achieve its intended purpose in clinical practice? Taken together, these questions are concerned with whether the benefits of the intervention in addressing a malady (here, PTSD) outweigh the known risks.

We addressed the effectiveness of different interventions in the previous section. To recapitulate, while more research is necessary, there is cause for cautious optimism that certain memory-modifying interventions may indeed bring relief from symptoms of PTSD.

With regard to safety, the question becomes more contextual. Different interventions, each with a different side-effect profile, can be used to interfere with the consolidation and reconsolidation of memories. Even the beta-blocker propranolol, generally regarded a relatively benign medication,Footnote ⁸⁴ has some side effects. Indeed, because it is used to treat certain cardiovascular conditions, it must necessarily have cardiovascular side effects when used to produce neurocognitive effects.

Safety is a particularly pressing issue when it comes to prophylaxis. An over-generous prophylactic use would mean that many people would be exposed to the side effects of the intervention without gaining any benefits. The problem is that it is difficult to predict if and when PTSD might develop: not all traumatic events are so serious as to trigger PTSD, and not all people experiencing the same event develop PTSD.Footnote ⁸⁵ Thus it is not clear who should receive prophylaxis.

The magnitude of this problem depends on whether we are concerned with pre-exposure prophylaxis (that is, in anticipation of a traumatic event) or post-exposure prophylaxis (that is, immediately after a traumatic event and in any event before symptoms of PTSD have developed). Pre-exposure prophylaxis is clearly more challenging because there is an added variable: not knowing if and when a traumatic event might take place. Thus, effective prophylaxis would require the use of long-acting interventions or keeping the person on a particular medication for days on end. Because most side effects of medications are dose-dependent, a prolonged administration of a medication is more likely to produce adverse effects.Footnote ⁸⁶

Aside from the consequences of long-term medication use, the medications that are likely candidates for MMTs may have an immediate operational impact, such as an impact on the ability of a soldier to perform tactically important tasks at a predictably high level. We can use beta-blockers as an illustration.

First, beta-blockers have physical side effects because they reduce heart rate. Thus, beta-blockers would likely improve the accuracy of a sniper, as they would increase his or her ability to fire shots between heartbeats. Yet, through the same mechanism, beta-blockers would reduce the volume of oxygen that the cardiovascular system can deliver to the muscles. Thus, beta-blockers would inhibit exercise performance and impair the ability of soldiers to meet the physical demands of combat.Footnote ⁸⁷

Secondly, beta-blockers can have effects on behaviour and cognition.Footnote ⁸⁸ They interfere with the actions of stress hormones and as such can reduce arousal and feelings of anxiety. Stress hormones and arousal, however, “are central to the fight-or-flight response, and they trigger the heightened awareness necessary for soldiers to survive in combat situations”.Footnote ⁸⁹ Thus, beta-blockers might alter the fight-or-flight response, which has evolved as a survival mechanism, to a degree that it would place the soldier in greater danger in threatening circumstances.Footnote ⁹⁰

Finally, beta-blockers also affect decision-making,Footnote ⁹¹ raising the question as to whether they affect the way people resolve morally significant problems.Footnote ⁹² Recent studies indicate that propranolol leads to more deontological and less utilitarian decisions (at least in certain circumstances), and that it decreases response times and increases decisiveness.Footnote ⁹³ More impulsive and less consequentialist decision-making can pose problems for compliance with international humanitarian law. In particular, it might influence decision-making in circumstances where the law requires a fine consequentialist calculation, such as with the principle of proportionality, which requires balancing the anticipated military effect to be gained from an attack against the incidental loss caused to civilians and civilian objects.Footnote ⁹⁴ Looking prospectively, medications might cause people to make different decisions than they would otherwise. Looking retrospectively, this might affect the degree of moral responsibility that could be assigned to them afterwards.Footnote ⁹⁵

The situation with post-exposure prophylaxis is slightly different. In effect, one variable – whether or not a traumatic event will occur – has been removed, and thus there is no need to keep people on medications preventatively for long periods; a short-term intervention may be sufficient right after a distressing event has taken place. Also, the effects on physical performance and decision-making can be discounted relatively easily on the assumption that the person will not need to engage in physically strenuous or morally taxing activities while undergoing post-exposure prophylaxis.

That does not, of course, completely obviate the problem of not knowing whom to treat, but there are other measures that can be taken to reduce that uncertainty. In other contexts, for example as concerns infectious diseases, decisions about post-exposure prophylaxis are frequently made by means of a probabilistic risk assessment and on the basis of previously adopted guidelines. This is the case, for instance, in the event of a suspected exposure to the human immunodeficiency virus (HIV)Footnote ⁹⁶ or the rabies virus.Footnote ⁹⁷

Admittedly, the risk factors for developing PTSD are not as well understood as those for developing an HIV infection or rabies. However, already in one of the earliest clinical trials of propranolol as post-exposure prophylaxis, the administration of medication to people in a hospital emergency department after a traumatic event was based on psychological and physiological risk factors.Footnote ⁹⁸ As our understanding of risk factors improves, more reliable guidelines can be developed for PTSD prophylaxis.

In any event, post-exposure prophylaxis of PTSD and the treatment of PTSD once symptoms have emerged would require the administration of medication only a limited number of times. This would help mitigate some of the concerns about safety. Thus, as a general matter, the use of medications for memory modification is likely to be safer than the prolonged use of antidepressants, anxiolytics, antipsychotics and hypnotics currently used in the management of PTSD symptoms.

All biomedical interventions also raise the question of equitable access. Would all those who could benefit from the intervention be able to gain access to it? Again, the fairly limited number of times a medication would need to be administered as an MMT in case of post-exposure prophylaxis or treatment would likely mean that it is cheaper than a prolonged symptomatic treatment with various psychoactive medications. That could make it a more equitable treatment option.Footnote ⁹⁹

In conclusion, there are reasons to be cautious about PTSD prophylaxis, especially pre-exposure prophylaxis. The long-term effects of such prophylaxis are not necessarily well understood, and the immediate side effects could be problematic in the military context. Therefore, the benefits of such prophylaxis might not necessarily outweigh the risks. If post-exposure prophylaxis and, even more so, treatment at a stage where PTSD symptoms first appear are no less effective than pre-exposure prophylactic intervention, the former seems to be the more ethically defensible option.

Identity and authenticity

The principal concerns around memory modification go well beyond these relatively technical matters – which, moreover, are not unique to the interventions that might be used as MMTs – and raise broader questions. Perhaps the most prominent of these is the worry that by permitting our memories to be modified, “we might succeed in erasing real suffering at the risk of falsifying our perception of the world and undermining our true identity”.Footnote ¹⁰⁰ Much of this concern seems to be premised on the idea advanced by John Locke in the late seventeenth century that our memories are what define us as persons – what give us identities that persist in time.Footnote ¹⁰¹ The problem that arises here relates to two interconnected philosophical notions: authenticity and narrative identity.Footnote ¹⁰² These cannot be fully unpacked here, but the basic idea – we largely are what we remember about ourselves and the world around us – makes a lot of intuitive sense. Most people would probably agree that by erasing all our memories, we would commit a kind of cognitive suicide. Accordingly, by modifying some of our memories, we would in a significant way be transforming ourselves.

An argument frequently advanced to mitigate these concerns is that MMTs affect only conditioned defensive responses to threats (“emotional responses”) and leave episodic memories completely intact.Footnote ¹⁰³ The premise here is that mainly episodic memory contributes to our sense of self and, thus, if MMTs only affect conditioned responses, our identities would remain essentially unharmed. This argument is largely based on studies that have used beta-blockers. However, as discussed above, beta-blockers can also reduce the emotional enhancement of episodic memory. Furthermore, different MMTs, such as other medications or brain stimulation, can eradicate specific episodic memories altogether. MMTs can thus also impact episodic memories that contribute to our sense of identity. What's more, a problem in the argumentation is the assumption that “emotional responses” contribute less to our identity than episodic memories. This Cartesian view of separation between reason and emotion is false. Emotion and cognition are necessarily intertwined, to the degree that one cannot exist without the other.Footnote ¹⁰⁴ Changing learned emotional responses would, thus, also alter reasoning and our personal identity.

Regardless of the effects of MMTs on both conditioned responses and episodic memory, we submit that MMTs do not necessarily impinge on identity and authenticity to such a degree that we should shun the treatment. As discussed above, by nature memories are flexible: we forget most of what we learn, and memories can be highly inaccurate or even entirely false. Yet none of this has been a source of major philosophical concern. The inability to account for each moment of one's waking hours with complete accuracy and full emotional vigour neither undermines our identity nor hampers normal functioning in daily life.Footnote ¹⁰⁵ Quite the contrary, the flexibility of memory is adaptive and aids optimal decision-making in the future. Memory flexibility thus also constitutes a major way in which we build our autobiography and, by extension, our identity, which is fluid over time.

Even if concerns about identity might lead us to conclude that we ought not to have unfettered access to MMTs, this does not mean that they should not be used to treat PTSD. Indeed, the symptoms of PTSD can become so overwhelming as to fully consume a person's life: daily existence becomes haunted by memories of the past, resulting in major changes in personality and withdrawal from society to avoid stimuli that might trigger episodes of anxiety. Moreover, PTSD and suicidal behaviour are strongly correlated.Footnote ¹⁰⁶ Thus, PTSD poses a risk not only to personal identity, but also to life. In PTSD, trauma memory is thus clearly maladaptive. MMTs may allow people with PTSD to regain adaptive responses and return to normal life and, as such, may facilitate the maintenance of identity rather than undermine it.Footnote ¹⁰⁷

Normal recovery and traumatic growth

Another common concern about memory modification is that it would interfere with normal recovery from trauma – “working things through”, if you will.Footnote ¹⁰⁸ Moreover, going through such a process has certain adaptive consequences, which have been conceptualized as post-traumatic growth (PTG). This may be manifested in different ways, including “an increased appreciation for life in general, more meaningful interpersonal relationships, an increased sense of personal strength, changed priorities, and a richer existential and spiritual life”.Footnote ¹⁰⁹ MMTs would seem to deny traumatized persons the benefits of experiencing PTG,Footnote ¹¹⁰ which is said to be far more common in the wake of traumatic events than PTSD.Footnote ¹¹¹

For persons who suffer from PTSD, however, traumatic memories and the associated emotions are so powerful as to make it impossible to “work things through”.Footnote ¹¹² Their “experiences are simply tragic and terrifying, offering virtually no opportunity for redemption or transformation”, and “even if it is better to weave traumatic events into positive, life-affirming narratives, many people are never able to do so”.Footnote ¹¹³ Also, an individual who is afflicted to the point of functional loss or self-harm may simply be incapable of experiencing PTG.Footnote ¹¹⁴

Furthermore, it is by no means clear that MMTs and PTG are mutually exclusive. In fact, MMTs may lay the groundwork for recovery and PTG. It is perfectly possible that MMTs “might make it easier for trauma survivors to face and incorporate traumatic recollections, and in that sense could facilitate long-term adaptation”,Footnote ¹¹⁵ “may enable such people to make life transformations that they would be incapable of making in the absence of the medications”,Footnote ¹¹⁶ and “may aid in induction of PTG as well as relieve PTSD”.Footnote ¹¹⁷

There is more merit in the concern over a circumvention of natural processes when MMTs are used prophylactically. The question does arise as to whether we should be prepared to “replace this near-universal feature of human life [i.e. PTG] with a mass preventative pharmacotherapy that benefits a small minority of the population.”Footnote ¹¹⁸ Again, however, it is not clear whether MMTs would necessarily replace PTG; in persons at risk of PTSD, prophylactic MMTs may well contribute to ensuring that natural processes (including PTG) take place. To use an analogy, if a person fractures a bone, we do not allow nature to simply take its course. We may need to realign the fracture and set a cast in order for optimal healing to take place. Likewise, MMTs may return patients on a natural path to recovery.Footnote ¹¹⁹

A duty to remember?

Another major concern about MMTs is the risk of altering memories that we might be under a duty to preserve for the common good. Arguably, collective memories of atrocities, and of the carnage of war more generally, depend upon individuals retaining undiluted recollections of these events.Footnote ¹²⁰ Thus, modifying our memories of such events not only poses a risk to our personal identity “but also prevents the sharing of these narratives, which could potentially help others in society change and evolve”.Footnote ¹²¹

Lieutenant-General Roméo Dallaire, the commander of the United Nations Assistance Mission for Rwanda during the genocide, is sometimes used as an example.Footnote ¹²² Dallaire had been put in an impossible situation – the wholly inadequate forces that had been placed under his command were unable to stop the slaughter of hundreds of thousands of Tutsis and moderate Hutus. As Dallaire himself put it in a poignant book about the genocide, he and his troops were “reduced to the role of accountants keeping track of how many were being killed”.Footnote ¹²³

Through the book and many public appearances, Dallaire became a powerful advocate for humanitarian intervention – but he also suffered, and continues to suffer, from PTSD; indeed, his anguish has led him to self-harm.Footnote ¹²⁴ One commentator speculates that had Dallaire “taken memory-dampening agents, [he] may not have been able to achieve the same level of influence on society”.Footnote ¹²⁵ On one view, Dallaire may have succeeded so well in telling the world about the plight of Rwanda because he is “the most powerful and untainted witness” to the genocide.Footnote ¹²⁶ On an alternative (much more troubling) view, some of Dallaire's effectiveness as an advocate may have derived from his own suffering. Thus, Dallaire's suffering might have in some ways been symbolic of how the international community had failed the Rwandans, and may have served as a reminder of this failure to that community. This point could be formulated more broadly, suggesting that having struggling veterans in our midst serves to remind the society of the horrors of war.

While we sympathize with the idea that society should not be disconnected from the conflicts that are fought on its behalf, treating service members as instruments in obtaining that goal fundamentally dehumanizes them. We agree with one prominent bioethicist who thinks that “[t]he notion that we need to have suffering martyrs among us is cruel and exploitative”.Footnote ¹²⁷ Also, there is undoubtedly “some hypocrisy in the contention that soldiers ought to bear painful trauma for what others have commanded them to do”.Footnote ¹²⁸

From a legal perspective, the problem with memory modification is that it may limit society's access to memory as evidence, such as eyewitness testimony.Footnote ¹²⁹ While this point is well taken, it should not be overemphasized. For one, the value of eyewitness testimony is probably overstated in the first place. Individuals’ recollections of events are less reliable than one might think. It is all too easy to think of memory as some sort of a documentary film that can be replayed in court as necessary, but the ability of humans to remember has evolved not so as to forensically document the past, but so as to prepare us for the future. Thus, memories get reinterpreted and reconfigured as new experiences become integrated into an autobiography. For this reason, eyewitness testimonies require – or should require – extensive corroborative evidence.

In any event, even recognizing that society sometimes has a reasonable expectation about accessing someone's memories, that right cannot be absolute. The interests of the society in obtaining the memory and the individual's interest in not suffering from traumatic memories need to be balanced. What is more, for post-trauma MMTs to work, the details of a traumatic memory would first have to be identified by a therapist prior to treatment. As such, there would be a detailed archive of memory prior to modification.

Furthermore, MMTs are unlikely to completely eradicate a memory. Realistically, were he to be treated with MMTs, Dallaire would no longer suffer (as much) but would still remember what had happened and that he had suffered, so as to be able to appreciate the importance of the memory. This likely would still leave him as a strong spokesperson for humanitarian intervention. Also, persons with PTSD often have difficulty recalling particular events and articulating their experiences as a coherent narrative; thus, PTSD treatment might not undermine but might instead enhance people's ability to meet the duty to remember.

A duty to suffer?

A slightly different need to preserve memories arguably arises with respect to people who have committed objectionable acts and feel pangs of guilt afterwards. Lady MacBeth has thus become something of a recurrent character in bioethical discussions on MMTs.Footnote ¹³⁰ There appears to be broad agreement that people should not have access to MMTs to “relieve anguish that is proportionate to their own actions”.Footnote ¹³¹ This seems uncontroversial inasmuch as such interventions are not meant to be available to anyone who simply wants to dampen undesirable and even troubling memories; rather, they are intended for people with maladaptive memories such as in the case of PTSD. Some of the commentary on this point might be interpreted as doubting the appropriateness of providing MMTs to persons who have developed PTSD as a result of their own wrongdoing.Footnote ¹³²

This line of thinking may be based on an idea that PTSD is some especially sharp form of guilt or remorse. This is a misconception. PTSD is a serious and potentially debilitating mental health condition, not merely a feeling or a state of mind. Leaving it untreated is problematic both from a prudential and an ethical perspective. As for the former, a strong association exists between PTSD symptoms and the risk of re-offending.Footnote ¹³³ Thus, however attractive PTSD symptoms may seem to some as a form of retribution, perpetuating the condition seems wholly counterproductive from the perspective of rehabilitating offenders and reintegrating them into society. From an ethical perspective, a hallmark of a civilized society is that it provides adequate health care to those who it has convicted of wrongdoing.Footnote ¹³⁴ Conversely, the idea that a medical practitioner would deny treatment to a patient not because of futility or shortage of resources but simply because of legal or ethical misgivings about the patient's prior conduct flies in the face of medical ethics.Footnote ¹³⁵

Indeed, it would not be acceptable to modify the standard of care so as to increase or maintain suffering that has been caused by the antisocial conduct of the person. For example, it would be inappropriate for a medical practitioner to remove a bullet without anaesthesia simply because the person was shot in a firefight with police. In fact, refusal to provide anaesthesia to a person on the basis of their criminal history would almost certainly breach the prohibition against torture or cruel, inhuman or degrading treatment or punishment.Footnote ¹³⁶

Even more dubiously, PTSD treatment has been questioned in the context of warfare. For example, one commentator has asked – rhetorically, we presume – “If soldiers did something that ended up with children getting killed, do you want to give them beta-blockers so that they can do it again?”Footnote ¹³⁷ The question itself is problematic. No one would deny that the death of children – indeed, anyone – in conflict is unfortunate and regrettable. Yet even the death of children does not necessarily amount to a wrongdoing on the part of the individual soldier. For example, under the law of armed conflict, children taking a direct part in hostilities can be lawfully targeted.Footnote ¹³⁸ Soldiers who find themselves in a position where their only viable course of action is to use lethal force against a child soldier would, no doubt, be seriously scarred and potentially at risk of PTSD.

In any event, the two problems identified with respect to criminals arise with even more vigour when it comes to soldiers. For one, veterans with PTSD are statistically more likely to engage in antisocial behaviour than veterans who do not have PTSD.Footnote ¹³⁹ Thus, again, leaving PTSD untreated could be highly counterproductive both in terms of soldiers continuing military service and re-entering civilian society. Furthermore, one expects the armed forces to provide every medical assistance available to physically wounded soldiers in an attempt to restore them to health and, alas, to allow them to fight another day. With this in mind, to deny PTSD treatment to a soldier because the treatment might permit them to return to combat is simply preposterous. A serious ethical problem would arise, however, if some form of MMT was applied prior to conflict with a view to generally morally desensitizing soldiers. Yet this would no longer be a problem about prevention or treatment of PTSD, which is the focus of this article.