As a 20-year-old college student, Mark Rosen was once given general anesthesia for chest surgery but was far from knocked out.
"I knew something was wrong, feeling them cutting," he told ABCNews.com in a 2008 interview. "I remember wanting to push away but you're paralyzed. You can't move, you can't open your eyes … the fright of being locked in."
He is now Dr. Rosen and vice chairman of anesthesiology at the University of California San Francisco Children's Hospital and places complete faith in modern anesthesia; a medical advancement that researchers are only beginning to understand fully.
His experience is rare, and doctors have since developed brain monitors that can gauge levels of consciousness, which underscores the complex science of keeping patients free from consciousness and pain without killing them.
The use of general anesthesia is a routine part of surgical operations at hospitals and medical facilities around the world, but the precise biological mechanisms of the drugs' effects on the brain are only now being analyzed.
In a review article published this week in the New England Journal of Medicine, scientists have for the first time used a range of disciplines, including neuroscience and sleep medicine, to lay the groundwork for better understanding of how anesthesia actually works.
Armed with the new information, doctors can speak more frankly and knowledgeably to patients.
"The biggest concern among patients is, "Am I going to wake up?" said lead study author Dr. Emery Brown, an anesthesiologist at Massachusetts General Hospital and professor at Massachusetts Institute of Technology.
"That happens extremely rarely but it's a fear everyone has. I think the way to assuage the fear is to know what we are doing. But we can't continue to comfort people if it's a black box and I assure you it's not going to go wrong."
This research may also shed light on treatments for neurological disorders such as depression, schizophrenia, Parkinson's disease and chronic pain syndrome. And, they say, it may also help doctors bring patients out of comas.
General anesthesia is a reversible coma, not sleep, Brown said, although doctors often tell their patients they are putting them to sleep in hopes of scaring them less.
"From a laymen's standpoint, you want to come in to surgery and basically know you are going to be well taken care of," Brown said. "We try to give patients the impression we understand what is going on, but we say you are going off to sleep when it turns out it's not sleep, it's more like a state of coma."
Modern anesthesia, which has been around for about 160 years, has long been considered one of medicine's greatest gift and it had its beginnings at Massachusetts General Hospital.
Historically, herbal extracts or alcohol was used to dull pain as patients underwent surgery. But in 1831, Englishman James Young Simpson discovered the sleep-inducing properties of chloroform. Its use spread and it was even administered when Queen Victoria gave birth to Prince Leopold in 1853. But because it was used by untrained practitioners, chloroform lead to many deaths.