I wrote recently that neuroplasticity has the potential to be very helpful to combat vets because a “plastic” brain that has been changed by trauma can continue to change. Good memories can layer over and alleviate the bad ones. My last blog on whitewater rafting as a therapy for post-traumatic stress disorder (PTSD) suggests that this concept works.

But there’s a downside that vets are particularly susceptible to. Dr. Norman Doidge, author of the best-selling book “The Brain That Changes Itself,” calls it “the plastic paradox.” Because the brain is neuroplastic, mental experiences can change it and create completely novel circuits in the brain. There’s a lot of flexibility in the brain, but not all change is good.  The same plasticity that can give rise to flexible behaviors can, if mental experiences are repeated over and over, lead to rigid, repetitive behaviors.

Doidge, a medical doctor and a psychiatrist affiliated with both the University of Toronto and Columbia University, says this occurs in vets with PTSD. PTSD is a neuroplastic disorder par excellence because a person with a functioning nervous system experiences an event, the meaning of which is so overwhelming to the mind that soon the brain is completely rewired by it.

Let’s walk through how this works.

First, the trauma of an intense firefight or your buddy dying in your arms overwhelms your brain, causing it to change its structure and function. It’s now on high alert for a new threat. “The event so overwhelmed the brain when it first occurred that it overwhelmed the circuitry that allows the victim to turn the event from a perception into a memory, something our brain normally does the moment an event is over,” Doidge told me.

And that’s the cause of flashbacks, Doidge says. “Each time people have ‘flashbacks,’ they are experiencing unfiled perceptions of the horrible event — not memories. (We mistakenly call them memories because they seem to be repeats of what happened, but subjectively, flashbacks are more like perceptions, and sometimes almost more like hallucinations.) And since the brain thinks the event is still happening, this triggers the threat system in the brain. Neurons that fire together wire together, so each time the flashback occurs, it more deeply connects the images involved in the flashback with the threat system. Soon the threat system is on when it shouldn’t be,” says Doidge.

With the threat system on high alert, vets don’t live normal lives. And this is generally accompanied by depression, anger and compromised thinking ability, which lead vets to isolate themselves. Doidge says: “As they withdraw from activities, the circuitry for those activities begins to weaken. (Another plastic principle is that it is a use-it-or-lose-it brain, and neuronal connections that are not reinforced will atrophy or weaken.) They might try and do high-level activities, but their brains have trouble with them. Soon they develop something called learned non-use. Learned non-use is not a form of laziness; it is what the brain takes away from repeated efforts to do something, and finding it can’t.”

That is to say, when the brain repeatedly tries and fails to do something, it deploys its resources in other areas. If a vet needs companionship, but his brain can’t force itself to mingle with other people in a crowd, it will ultimately quit trying. And so harmful habits can become part of learned behavior too, Doidge points out.

Compounding these problems is a lack of sleep. Many vets are plagued with nightmares, sometimes called night terrors, which are like sleeping flashbacks. Others are on alert waiting for a night attack or patrolling the perimeters of their backyards to keep their kids safe from the bad guys. But that lack of sleep inhibits healing.

“With the threat system so often on, screaming ’emergency,’ they can’t sleep normally, concentrate, do high-level thought, and they withdraw from their normal activities,” says Doidge. “This adds a new burden on the nervous system. Sleep is necessary for resetting the brain, consolidating new learning, working through trauma, and the healing and the immune system.”

That helps to explain why vets have been helped by devices like Alpha-Stim, which wafts an alpha wave through someone’s brain from earlobe to earlobe. At the Rimrock Foundation in Billings, Mont., in about 20 minutes of therapy, I watched a young drug addict and beating victim change from a tense young woman who couldn’t sleep to a very tired teenager who badly wanted a nap. Now there are also recordings that do pretty much the same thing.

So sleep helps the brain to restore some of the damage. Here are some other therapy suggestions from Doidge, whose book, “The Brain That Changes Itself: Stories of Personal Triumph from the Frontiers of Brain Science,” is about the neuroplasticity revolution and how it is helping people like our combat vets. It’s a remarkable book.

Doidge says: “What is required is a treatment that can do two things. We know that to actually change a circuit, at some point we have to activate it, and then it enters a more malleable state. And we have to activate it while the person’s threat system is turned down. A number of treatments can do this: Eye Movement Desensitization, and Reprocessing (if done while the person’s mental resources are maximized), a related treatment called Brainspotting by David Grand, some energy therapies, certain kinds of hypnosis, and a new treatment that has people read over detailed narratives of their traumas while taking (for a few hours) an old antihypertensive drug called Propranolol which quiets the autonomic nervous system. In many cases, they can all accomplish this successfully. These are all neuroplastic interventions because they use mental experience to alter brain circuits.”

So there you have it, one of the best neurological explanations of PTSD that I’ve seen. But we’re going to have to continue working on the therapies.