Post-traumatic stress disorder, PTSD, affects nearly 30 percent of troops who served in Iraq and Afghanistan. After they come home, these men and women often experience intense and fearful memories that they just can’t forget.

"It really changed my personality. War changes everybody," said Josh Lewis, a retired Marine sergeant.

"I mentally and emotionally became numb to adverse situations," said KeeShaun Coffey, a retired Navy religious program specialist.

Lewis had four tours of duty to the Middle East when he was in the Marines. During that time, he made friends and lost friends.

"Every time you lose a friend, you kind of lose a little bit of yourself," Lewis said.

When he returned to civilian life, Lewis was diagnosed with a traumatic brain injury and PTSD.

"I had tremendous headaches that just took me out for a day or two," Lewis said. "I was basically stuck at home in bed, just trying to get through it."

Coffey saw bodies every day, but when his best friend became one of them, Coffey realized something was wrong.

"I couldn't cry. I didn’t know what to do," he said.

Coffey withdrew from the Navy, but he also struggled with PTSD when he returned to his normal life.

"I was just having nightmares to where I just slept in my closet," Coffey explained.

Dr. John Hart is studying ways to help people like Coffey and Lewis.

"PTSD, I look at it as a memory disorder. There's a horrible memory that is now locked into your head that produces a fearful response," said Hart, medical science director, Center for BrainHealth, The University of Texas at Dallas.

Hart and researchers at the Center for BrainHealth have recently discovered how bad memories are stored in the brain.

"We found brain waves that hook the fear center to the memory center," Hart said.

When the fear center of the brain, called the amygdala , attaches to memory parts, it sends a signal with a rhythm of four hertz. To disrupt this signal, doctors are using repetitive transcranial magnetic stimulation.

A device is placed on the participant's head. A slow electrical current travels to the front part of the brain to target the amygdala and reduce the fear area's attaching to the memory area.

"That's how your brain knows that should be a fearful thing. It attaches to the memory," Hart explained.

Another way to help is a method called cognitive processing therapy. First, participants talk about their fears and relive them in a safe setting.

"The pain is the cure for the pain. The anxiety is the cure for the anxiety," said Tina Bass, psychotherapist, The Center for BrainHealth, The University of Texas at Dallas.

Therapists also use a brain-training program to help men and women deal with stress by teaching them how to focus their thoughts and come up with solutions.

In a study, veterans who participated in the program reported up to a 50 percent improvement in mood.

Lewis participated in this SMART training and went from having a headache every six weeks to having one every six months. He said he's learned to slow down his thinking.

"We kind of learn to zoom out and look at the problem as a whole," Lewis said.

Coffey said the magnetics treatment has helped him cope with his emotions.