But these improvements are accompanied by an emotional toll.

"The fact is that you always have people who develop post-traumatic reactions after certain events," Neria said. "For those people, reactivation and re-exposure is tough and can either lead them to some more debilitating pain and more fretful memories, especially for the bereaved. Those victim groups are increasing in number and size over time. That's what you see in nations like Israel — you have highly experienced response systems, along with increasing numbers of people who are suffering."

Contributing to both aspects of the trauma, since 9/11, is social media.

"We access information so rapidly and so effectively through social media, so it's kind of helpful in a way," Neria said. "It helps us to regain a kind of control. We are more updated and more informed more quickly than before. Information is empowering and it's very, very important to us."

With smart phones, he said, "we can make better plans — we can deal with transportation and flights, and hopefully we can protect our families better because of those tools."

But again, where we benefit on a practical level, we pay emotionally.

"Perhaps we are over flooded with gruesome images," he said, "and perhaps we are more anxious because of that."

Countless cameras were already out at the marathon's finish line when the bombs exploded, so gruesome images abounded minutes after the blasts. Add social media like Twitter and Facebook, where these photos can reach audiences without going through the filter of mainstream media, and you've got a public that's taking in a steady stream of some very disturbing images.

Roxane Cohen Silver, a professor in the department of psychology and social behavior at the University of California-Irvine, said she avoids Twitter and Facebook for this reason. Still not known, she said, is exactly what the effect of social media is in such cases.

"We want to explore some of that," Cohen Silver said. "We really don't know."

But she has studied the effects of media related to 9/11 and the Iraq invasion.

"We found that a steady diet of those images was connected to more physical and mental effects in three years," she said. "I would discourage anyone from a steady diet of these images."

'What's The Next Target?'

A small group in the Boston Marathon ran to remember the 26 victims of the Sandy Hook Elementary School shootings. Among them was Newtown pediatrician Laura Nowacki, 47, who took part in a ceremony days before the race to dedicate the 26th mile to Newtown.

Nowacki's husband, Newtown dentist David Nowacki, wanted to surprise her at the finish line, so he brought their four children, ranging from 10 to 16 years old, to the race. They secured seats in the VIP stands, very close to the site of the first explosion.

Fortunately, Nowacki finished the race about a half hour before the first blast. The family was back in her hotel room on the eighth floor of the Four Seasons Hotel Boston, down Boylston Street a few blocks from the finish line. She got a news text alert about the bomb.

"When we got the text, I foolishly turned on the TV and saw where it was and we had to turn off the TV right away because that upset especially my 10-year-old daughter because she was in Sandy Hook," Nowacki said.

Nowacki called the front desk of the hotel, ready to respond to the scene as a medical professional — just as she did after the Sandy Hook shooting — but learned that the scene was already blockaded.

"You go into that doctor mode, but at the same time I'm staring at my 10-year-old who just went through this," Nowacki said. "So, the parent mode absolutely won out here."

She would have stayed the night in a Boston hotel had her children not been there.