It’s hard for most of us to imagine what goes through the mind of a hoarder.

But a new study has captured images of exactly what happens inside a hoarder’s mind. The findings could eventually lead to more effective treatments for this disabling disorder. In the meantime, they shed light on the subtleties of a baffling condition.

Published in the August issue of the Archives of General Psychiatry (a journal of the American Medical Association), the study was led by David Tolin, director of the Anxiety Disorders Center at the Institute of Living, a mental-health research and treatment facility affiliated with Hartford Hospital in Hartford, Conn. Tolin and his team set out to determine whether brain activity among people with hoarding disorder looked similar to that of people with obsessive-compulsive disorder (OCD) as they decide whether to keep or discard what would typically be considered trivial items: pieces of junk mail and outdated newspapers.

Tolin and his team recruited 107 people — 43 with hoarding disorder, 31 with OCD and 33 “healthy” people — to serve as controls. They asked them to bring from home an assortment of junk mail and newspapers that belonged to them; in the lab, the researchers assembled a set of similar items that did not belong to any of the study participants.

All the items were scanned so they could be shown to the participants on screens. The team then used functional MRI to document the activity in participants’ brains as they were shown images of the items, one at a time, and asked to decide whether to keep the item or discard it. They were told that if they chose to discard it, the item would be shredded, so these decisions were final. Each of the images of the items was labeled “yours” or “ours” to help study subjects recognize the ones they’d brought from home.

Judging from earlier research findings, the team hypothesized that the hoarders’ brain activity would be similar to that of the people with OCD and different from that of the healthy people.

What they found instead was illuminating. When presented with objects they did not own, the people with hoarding disorder displayed less activity in certain key areas of the brain than was seen in people with OCD or healthy subjects. Those brain regions — the anterior cingulated cortex and insula — are, according to the study, “thought to be part of a functionally connected network of structures used to identify the emotional significance of a stimulus, generate an emotional response, and regulate affective state.” The low activity seen there suggests that the subjects weren’t very engaged in making decisions about stuff they didn’t own. But when they made choices about their own junk mail and newspapers, activity in those parts of the brain was much greater in those with hoarding disorder than those without.

Tolin suggests that that brain activity can be seen playing out in television shows such as A&E’s “Hoarders” (on which Tolin has appeared as an expert). Those shows typically start with the viewers tagging along on a tour of “the person’s horribly cluttered home,” Tolin said in a phone interview. The viewer may be horrified, he says, but the person with the hoarding problem appears not to be bothered by the clutter, no matter how horrific it is. That lack of engagement, which Tolin likens to a similar phenomenon among people with autism, is mirrored in the low activity seen in the brain scans of hoarders looking at items not belonging to them.

But that all changes when the hoarder is asked to start making choices about his or her stuff. “They’re paralyzed by what most of us see as an easy decision,” Tolin said. That’s when that heightened brain activity observed in the study when hoarders were asked to decide the fate of their own belongings kicks in.

The research is timely, and not just because television shows such as “Hoarders” have called attention to the phenomenon. The American Psychiatric Association is preparing for the May 2013 publication of the fifth edition of its Diagnostic and Statistical Manual of Mental Disorders, or DSM-V. That influential document spells out criteria for diagnosing and treating mental illnesses. As the introduction to the study notes, discussion persists as to whether the DSM-V should designate hoarding disorder as a form of OCD or as a separate entity.

Tolin — author of the 2007 book “Buried in Treasures: Help for Compulsive Acquiring, Saving, and Hoarding.” — says this research, along with lots of other research yet to be done, may eventually lead to better treatments for hoarding disorder. “We treat OCD really well, through medications and behavior therapy,” he said. But in applying OCD treatments to hoarding disorder, he said, “We’ve seen a lot of examples of what doesn’t work.”