What causes PTSD, and why can a traumatic memory sometimes feel as though it is happening again? Discover how trauma can affect the brain, why PTSD memories can be experienced differently from ordinary memories, and what causes flashbacks and re-experiencing.
Post-Traumatic Stress Disorder (PTSD) is a complex response to trauma that can affect the way a person thinks, feels, remembers and responds to the world around them.
Most people who experience something traumatic do not go on to develop PTSD. However, for some people, the effects of trauma continue long after the event has ended. Memories can return unexpectedly, nightmares can interrupt sleep and seemingly ordinary sights, sounds or sensations can trigger an intense reaction.
One of the most distressing symptoms of PTSD is re-experiencing—when aspects of the traumatic experience return involuntarily. This can include intrusive memories, nightmares, distressing images and, in some cases, flashbacks.
But why can a memory from the past sometimes feel as though it is happening right now?
To understand this, it helps to look at what happens when the brain experiences something traumatic.
What causes PTSD?
PTSD can develop after experiencing or witnessing a traumatic event.
Trauma can include experiences such as:
- A serious accident
- Physical or sexual assault
- Abuse
- Military combat
- Serious illness or medical trauma
- Natural disasters
- Witnessing someone being seriously injured or killed
- Childhood trauma
- Experiencing or witnessing violence
- Other situations involving serious threat, injury or danger
PTSD can also develop after repeated or extreme exposure to traumatic material, particularly as part of certain occupations.
However, experiencing trauma does not automatically mean that someone will develop PTSD. People respond to traumatic experiences in different ways, and a range of psychological, biological and environmental factors can influence whether PTSD develops. Symptoms can appear soon after the event, but they can also emerge months or even years later.
What happens in the brain during a traumatic experience?
When something frightening or life-threatening happens, the brain’s priority is not to create a perfectly organised autobiographical memory. Its priority is survival.
The brain rapidly assesses potential danger and activates systems that prepare the body to respond. This can involve the familiar fight, flight or freeze response.
Stress hormones and other neurochemical changes help the brain pay close attention to what is happening. Sounds, smells, sights, physical sensations and other details associated with the threat can become strongly linked with the emotional response to the event.
This is an extremely useful survival mechanism. If you were in danger and escaped, your brain would want to remember enough about the situation to recognise a similar danger in the future. The problem arises when the danger has passed but the brain continues to respond to reminders as though the threat may be happening again.
Research into PTSD has identified changes involving interconnected brain systems including the amygdala, hippocampus and prefrontal cortex, which are involved in threat detection, emotional responses, memory and putting experiences into context.
The amygdala: the brain’s alarm system
The amygdala plays an important role in processing emotional significance, particularly threat and fear. During a traumatic experience, the amygdala becomes highly active as the brain attempts to identify and respond to danger.
It can also help create strong associations between the traumatic event and details surrounding it. For example, imagine someone is involved in a serious road accident.
Their brain may associate the experience with:
- The sound of screeching tyres
- The smell of petrol
- The sensation of being trapped
- The sound of breaking glass
- A particular road
- The sight of an approaching vehicle
Later, one of these things might activate the brain’s alarm system even though there is no longer any actual danger. Research has found increased amygdala activity in PTSD alongside changes in areas involved in emotional regulation and contextual processing.
The hippocampus: putting memories into context
The hippocampus is involved in memory and, importantly, in helping us understand the context in which something happened.
It helps us distinguish between:
“This happened in the past.”
and
“This is happening now.”
This distinction is particularly important when we think about PTSD flashbacks.
A normal autobiographical memory usually has a sense of time and place attached to it. You can remember your first day at school, for example, while knowing that you are remembering something that happened years ago. You are not experiencing the first day of school again. You are remembering it.
Traumatic memories can sometimes be experienced differently. Research suggests that trauma-related memories can involve unusually strong sensory and emotional components, while contextual processing can be disrupted. This may help explain why some traumatic memories can feel extraordinarily vivid and immediate.
The prefrontal cortex: helping us understand what is happening now
The prefrontal cortex is involved in many higher-level functions, including decision-making, emotional regulation and putting information into context.
One model of PTSD suggests that changes in communication between the prefrontal cortex and the amygdala can contribute to difficulties regulating fear responses.
Research has found patterns involving increased amygdala activity and altered prefrontal activity in people with PTSD, although PTSD is complex and cannot be explained by a simple “one part of the brain is switched on and another is switched off” model.
The important point is that the systems responsible for detecting danger and the systems helping us recognise “this is a memory; I am safe now” may not be working together in the same way they normally would.
Why does a PTSD memory feel as though it is happening now?
This is one of the most important questions when trying to understand PTSD. Ordinary memories are usually experienced as something that happened then. A PTSD flashback can feel as though something is happening now.
A person might know intellectually that they are at home, at work or somewhere else entirely, but their emotional and physical experience can tell them something very different. Their heart may race. They may sweat or shake. They may feel terrified. They may hear or see aspects of the traumatic experience. They may feel the same physical sensations they experienced during the original event.
For a moment, the distinction between remembering and experiencing can become blurred.
The National Center for PTSD describes flashbacks as experiences in which someone feels as though they are actually back at the time and place of the traumatic event. This is why telling someone experiencing a flashback to simply “remember that it happened years ago” may not be enough.
Their brain is responding to the memory as a present threat.
How are traumatic memories different from ordinary memories?
It is important not to think of traumatic memories as simply being “stored incorrectly”.
Memory is complicated, and researchers continue to investigate exactly how traumatic memories are represented and retrieved. However, research suggests that PTSD involves differences in the interaction between emotional memory, contextual memory and threat processing.
A useful way of understanding the difference is to think about two memories.
An ordinary memory
You might think:
“I remember the accident. It happened three years ago.”
You can remember what happened while remaining aware that you are safe in the present.
A trauma-related flashback
The experience might instead feel like:
“It’s happening again.”
The person may experience images, sounds, physical sensations and emotions associated with the original event, sometimes with a reduced awareness that these experiences are memories from the past. This doesn’t mean the person has forgotten that the trauma happened in the past. Rather, the memory has become powerfully linked with the brain’s threat response.
Why can seemingly unrelated things trigger PTSD?
After trauma, the brain can learn associations between danger and many aspects of the surrounding environment. This is sometimes described as fear conditioning.
If a particular sound was present during a traumatic event, for example, the brain may subsequently treat that sound as a warning signal. Importantly, the trigger doesn’t necessarily have to be an exact reproduction of the original situation. The brain can generalise from what happened.
Someone involved in a car accident might therefore react not only to the exact location of the accident but also to:
- Driving at night
- Heavy traffic
- Rain
- The sound of brakes
- Being a passenger
- Sitting in a particular type of car
The response can happen before the person has consciously worked out why they are frightened.
Research suggests that trauma can create strong associations between cues present during the traumatic experience and fear responses, so that later reminders can reactivate emotional and physical aspects of the experience.
What is re-experiencing in PTSD?
Re-experiencing is one of the characteristic groups of PTSD symptoms.
It can include:
- Intrusive memories
- Distressing images
- Nightmares
- Strong emotional reactions to reminders
- Physical reactions to reminders
- Flashbacks
The experience can range from briefly being reminded of what happened to feeling completely immersed in the traumatic experience. The National Center for PTSD explains that trauma reminders can include things such as sounds, smells and visual cues, and that these can cause emotional and physical reactions.
What does a PTSD flashback feel like?
A flashback can be extremely distressing.
Someone experiencing one may feel:
- Frightened
- Panicked
- Trapped
- Overwhelmed
- Confused
- Physically unsafe
- As though they are back in the traumatic situation
They may experience vivid images, sounds, smells or bodily sensations connected with the trauma. Their heart may race and their body may enter a state of high alert. Some people describe flashbacks as being suddenly transported back to the traumatic experience. Others experience something less visually vivid but still intensely emotional or physical.
There isn’t one universal experience of a flashback.
PTSD isn’t simply “remembering something upsetting”
This distinction is important. Someone can remember a traumatic experience without having PTSD. They might feel sad, angry or upset when thinking about it while still knowing:
“That happened in the past.”
PTSD involves a much broader pattern of symptoms, including re-experiencing, avoidance, changes in mood and thinking, and increased arousal or reactivity.
The NHS describes PTSD as involving symptoms such as repeatedly reliving traumatic experiences, nightmares and flashbacks, alongside other symptoms.
So although everyone can experience difficult memories, PTSD is more than having a bad memory of something frightening.
Why doesn’t the brain simply recognise that the danger has passed?
The brain’s response to trauma is designed to protect us.
Imagine that a person has survived a dangerous situation. Their brain has effectively learned:
“That situation was dangerous. Don’t let this happen again.”
If a reminder appears later, the brain may respond rapidly before the conscious mind has had an opportunity to analyse the situation. This is potentially protective. If the rustling of leaves really did indicate a predator, for example, it would be safer to react first and investigate afterwards.
After trauma, however, this protective system can become over-sensitive. A harmless reminder can activate the same alarm system. The person may therefore experience:
“Danger!”
before their conscious mind has processed:
“I’m safe. This reminds me of something that happened in the past.”
This helps explain why PTSD can feel so involuntary.
Can PTSD develop after one traumatic event?
Yes. PTSD can develop after a single traumatic experience, but it can also follow repeated or prolonged trauma. The likelihood of developing PTSD varies according to the individual and the nature and circumstances of the trauma.
Some people experience an extremely traumatic event and recover without developing PTSD. Others can develop significant symptoms following an experience that may appear less severe to someone else.
There is no useful hierarchy of trauma that tells us how someone “should” respond.
The person’s experience and response are what matter.
Why do some people develop PTSD while others don’t?
There isn’t one single explanation. Research suggests that PTSD involves an interaction between biological, psychological and environmental factors.
These may include:
- The nature and severity of the trauma
- Previous traumatic experiences
- Previous mental health difficulties
- Genetics and individual vulnerability
- The person’s circumstances at the time
- The amount of support available afterwards
- Ongoing stress
- The person’s ability to feel safe following the event
It is therefore important not to assume that someone who develops PTSD is somehow weaker than someone who doesn’t. PTSD is not a sign of weakness. It is a complex response to trauma involving changes in how the brain processes threat, emotion and memory.
Can PTSD memories change?
The brain is capable of learning throughout life. Memories aren’t necessarily fixed, unchanging recordings of the past.
When a memory is recalled, it can be influenced by the context in which it is remembered and by new learning.
This is one reason why trauma-focused psychological therapies can be helpful for PTSD.
Treatment can help people develop new associations between trauma reminders and safety, rather than continuing to respond to reminders as though the original danger is still present. Research into fear extinction and new safety learning is an important part of understanding PTSD recovery.
Can hypnotherapy help with PTSD and traumatic memories?
Hypnotherapy may be used as part of an individualised therapeutic approach for some people experiencing trauma-related difficulties.
Hypnosis involves focused attention and relaxation and can be used therapeutically to help someone develop a greater sense of calm and safety. Depending on the individual and the therapist’s training, hypnotherapy may incorporate techniques designed to:
- Reduce anxiety and physiological arousal
- Develop relaxation skills
- Increase feelings of safety
- Change unhelpful emotional responses
- Work with distressing memories
- Develop more helpful responses to reminders
- Focus on the person’s ability to move forwards
The Rewind Technique is another approach sometimes used when working with trauma and PTSD. It aims to reduce the emotional response associated with a traumatic memory without requiring someone to repeatedly describe every detail of the traumatic experience.
However, PTSD is a complex mental health condition and hypnotherapy is not a guaranteed cure or appropriate for everyone.
If you believe you may have PTSD, it is important to speak to your GP or an appropriately qualified mental health professional about your symptoms and the treatment options available to you.
Understanding PTSD Can Be the First Step Towards Change
PTSD can make the past feel as though it is still happening in the present. A sound, smell, image or situation can activate the brain’s threat system and suddenly bring back emotions, physical sensations or memories associated with what happened.
When you understand that response, it becomes easier to see that the person experiencing a flashback isn’t choosing to react that way. Their brain is attempting to protect them. The traumatic experience is in the past, but the brain may still be responding as though it needs to protect them from the same danger.
With appropriate support and treatment, it is possible to learn new responses to trauma reminders and develop a greater sense of safety in the present.
If you are experiencing symptoms of PTSD, flashbacks or intrusive memories, speak to your GP or an appropriately qualified healthcare professional for advice about the most appropriate support for you.
