Editor's note: Dr. Charles Raison, CNNhealth's mental health expert, is an associate professor of psychiatry at the University of Arizona in Tucson.
(CNN) -- The brain is by far the most complex thing that we know of in the universe.
And yet, for all its complexity, sometimes the brain responds to events in ways that are so remarkably predictable that we can use these responses to help people who are suffering.
Nowhere is this more true than in what we know about how the brain, along with its close attendants, the mind and the body, responds to catastrophic traumas such as the shootings Friday outside the Empire State Building in New York.
Before talking about the predictable way that the brain responds to traumas, it is also important to emphasize that all of us have complex and conflicting responses to horrific events such as mass shootings.
We feel sick with pain for the victims and distressed at the apparent senselessness of the violence. But we may also be deeply moved by the bravery of others at the scene or encouraged by the solidarity shown after the event.
Through this warren of conflicting feelings, however, a single motive arises in most of us driven by the human brain's natural sense of empathy. We want to help those directly affected by the tragedy. We want to know who to help and how to help them.
The first and perhaps most important thing to know in this regard is that most people who live through an unexpected, devastating and life-threatening situation such as a shooting suffer emotionally for various periods of time but do not develop a chronic psychiatric condition that requires professional intervention.
In this way, people are remarkably resilient. They will be fine with our love and care.
Unfortunately, a significant minority of traumatized people will suffer terribly and for an extended period as a result of developing post-traumatic stress disorder, or PTSD.
People with PTSD are afflicted with three primary types of symptoms.
The first type of symptoms involves all manner of intrusive memories of the event that often come with startling clarity via flashbacks and nightmares. Along with anything else that reminds a person of the trauma, these intrusive memories produce profound psychological distress and physical symptoms, such as a pounding heart.
The second type of symptoms revolves around avoidance and emotional numbing.
Bedeviled as they are by unwanted memories, images, nightmares and flashbacks that keep the terrifying reality of their experience emotionally alive for them, people with PTSD often go to heroic lengths to avoid anything in the personal or physical environment that reminds them of the trauma.
They often also report feeling emotionally deadened, unable to love and disinterested in things others find pleasurable. Often they feel like they will die young or have less of a future than other people.
The third and final symptom domain of PTSD is known as hyperarousal. Hyperarousal symptoms include difficulty falling or staying asleep, irritability or outbursts of anger, difficulty concentrating, being hypervigilant and finally, demonstrating an exaggerated startle response.
These PTSD symptoms usually don't travel alone, unfortunately, but are frequently accompanied by depression and difficulties with drugs and alcohol.
So how can we predict who is in danger of developing PTSD after experiencing something horrific such as a mass shooting?
We want to be able to predict this, because it will help intervene early on in the lives of people most in danger of making a poor recovery from the event. Fortunately, we've got a lot of scientific evidence to help guide us in identifying those at high risk for PTSD.
First and foremost, people who have tremendous emotional upset immediately after the traumatic event are at much greater risk of going on to develop PTSD than are those who respond with cooler heads.
It is absolutely not the case that people who are "cool, calm and collected" at the time of the trauma are setting themselves up for later trouble. Quite the contrary.
People who cope well in the minutes, days and weeks after a trauma typically do well over the long term. On the other hand, people who respond with immediate terror or who become "emotionally unglued" after the event are much more likely to continue having difficulties as the months and years roll on.
There is another symptom of acute trauma that can be easily missed if you are not on the lookout for it that strongly predicts the development of later PTSD. In layman's parlance, we might call it "being spaced out." More technically, we call it dissociation.
When people dissociate, things come apart in a variety of ways.
Often they feel separated from themselves, as if they are watching themselves from some outside vantage point. Frequently they feel that there is some type of invisible wall between themselves and the rest of the world. Sometimes they will feel that everything in the world, including themselves, is somehow unreal.
I've heard patients describe this experience as being like looking at the world through the wrong end of a telescope, so that everything seems smaller and distorted. In extreme instances, people so thoroughly lose track of things that they develop amnesia.
As we care for friends or loved ones who have experienced a trauma, it is of utmost importance that we keep an eye out for the development of any of these types of symptoms.
Usually we have to ask people directly about them. In my experience, people are often not even fully aware that they are experiencing dissociation, perhaps because it is so strange that they don't know how to think about it, perhaps because they are "dissociated" from their dissociation.
So let me try to boil it down to a simple recommendation.
People who respond to a horrific trauma with normal upset and anxiety need love, support and space to work through their feelings. On the other hand, people who respond with overwhelming feelings of terror, who are emotionally overwhelmed and/or who experience dissociative symptoms should be encouraged to find competent professional help immediately before these symptoms transform over time into PTSD.
It is so important that we find competent professional help for those at risk following a trauma, because early intervention, which can take the form of medications, therapy or a combination of the two, can really help people metabolize their horror and loss in ways that will provide them with a significantly happier and less impaired future.