BOSTON — We see pain portrayed in many ways in film — from frightening to suspenseful, and even comical.
"Pain is a fundamental sensation that is critical for survival," says Dr. Anne Louise Oaklander, a pain specialist at Massachusetts General Hospital.
"Pain is good because it's bad,” she says. "And it's the badness, the unpleasantness, the horrible emotions that are evoked when we feel pain that make it work so well."
Pain can even be mysterious.
Shelly Slate Tworoger, a 31-year-old with a Ph.D., led an active outdoor life until a year and a half ago when she had a simple operation to remove a bunion from her toe. Since the surgery, she has suffered debilitating pain — even though X-rays can find no reason for it.
"It'll feel like when I take a step that I'm walking on needles or nails," Tworoger says. "Someone's, you know, pushing needles up into my foot."
Nothing relieves it.
Dr. Oaklander, who treats her, says to understand such chronic pain we need to consider the very nature of pain.
Interactive: Take a tour of the brain For many years doctors have known the basics of pain perception. Specialized nerves throughout the body detect then pain and send a signal up through the spinal cord to the brain.
That is correct, but scientists now know it is only a small part of the story. Lots of new research shows that the brain plays the critical role.
"There are connections with the emotional parts of the brain," Oaklander says, "So that when we feel pain, it might make us sad or make us cry out or scream. It prompts fear."
Most of the time pain is temporary. But sometimes, for people like Tworoger, the complex interactions go haywire for unknown reasons, leading to chronic pain.
"I try to focus on the things that I appreciate and that are good in my life," Tworoger says. “But, you know, not everyday is a good day."
Dr. Oaklander believes she will eventually be able to treat Tworoger, but says research will someday find far better methods to cure such difficult constant pain.
© 2013 NBCNews.com Reprints