Suicide is the third leading cause of death among adolescents and young adults, yet there are no clear answers to what compels people to take their lives. It's a question that drives the research of Harvard University psychologist Matthew K. Nock, PhD, who began studying the topic as a Yale clinical psychology doctoral student.

Nock worked with violent, suicidal and self-injuring patients at Springfield Psychiatric Hospital in London during a semester abroad. Eager to learn more about what leads to suicidal behavior, Nock scoured the scientific literature for conclusive information on suicide prediction and best treatment approaches.

"I realized then that there was a lot we didn't know about why people hurt themselves," he says. "I became really motivated to try to do all I can to understand suicide."

Since then, Nock, 38, has generated some of the most innovative and important research to date on suicide and self-harm, which earned him a prestigious $500,000 MacArthur Fellowship in September. The five-year "genius grant" supports scholars and others who are doing exceptionally creative and promising work. The prize will allow Nock to expand his efforts to tease out the predictors of self-injury and suicide and focus on his most recent work to measure thoughts of self-injury and suicide in real time through the use of digital diaries and other technology.

"These are thoughts and behaviors that are really tough to capture," says Nock, editor of the 2009 book "Understanding Non-Suicidal Self-Injury" (APA Books). "We can't ethically induce them in the lab, so we really need to be creative in how we capture these things out in nature."

For the past two years, Nock and his research team have been using electronic diaries and portable heart rate monitors to gauge people's emotional and physical states before, during and after self-injury episodes. So far, his findings support what many people struggling with self-injury have noted for years — that self-harming soothes them.

Data show that there is increased arousal right before self-injury, and a huge decrease right after, says Nock.

"That change is much sharper than what we see when people engage in other behaviors to try to relax, like meditation or reading a book or deep breathing," he says.

Nock and his team have also found that little time elapses between when adolescents first think about hurting themselves and then try it, and that these youth aren't experiencing much pain — if any at all — when they cut or burn themselves.

"Self-injurers ... can tolerate much more pain than noninjurers," he says.

When he's not in his Harvard lab or teaching classes, Nock is an investigator for a large-scale study of suicide risk for the U.S. Army, known as STARRS (the Study to Assess Risk and Resilience in Servicemembers). With researchers from the National Institute of Mental Health, the Army and several universities, Nock is using the military's wealth of health and service data to investigate soldier suicides from the last five years.

He and his colleagues are sifting through information on everything from a soldier's military rank and promotion history to dental and medical records. Fusing this data will hopefully reveal clues as to what prompted these particular soldiers to choose suicide while others responded with resilience, says Nock.

"We are also interviewing family members and supervisors of these soldiers to see if we can paint the picture of what was happening with them," says Nock.

Fellow STARRS investigator Ronald C. Kessler, PhD, says Nock brings "a rare combination of intellectual breadth and depth" to such an important study. "He works across the spectrum from studies of neurobiological substrates to in-depth studies of clinical cases to studies of enormous epidemiological samples," Kessler says. "I don't know anyone who covers this range, let alone someone who does so in a way that makes important contributions to each of these areas."

Nock's graduate school adviser and mentor, Alan E. Kazdin, PhD, of Yale University, agrees that the MacArthur Foundation made a wise investment. "Matt can put ideas together in a comprehensive theory that most people would not ever think of doing," says Kazdin. "He is the leading clinical psychologist in the country, and No. 2 is too far away to even see him."