Excerpted from Stuff by Randy O. Frost and Gail Steketee. Copyright © 2010 by Randy O. Frost and Gail Steketee. Re­printed by permission of Houghton Mifflin Harcourt Publishing. All rights reserved.

This excerpt is a sample from DISCOVER's special Brain issue, available only on newsstands through June 28.

We could have found the apartment just by following the powerful musty odor that hit us as we stepped out of the elevator. When we got to the door, my guide knocked. No answer. She knocked again, then a third time. Finally, a small voice inside said, “Who’s there?”

“It’s Susan, the social worker. We’re here with the cleaning crew. They’re here to clean out your apartment.”

“Daniel’s not here,” the voice behind the door told us. “He went to get us breakfast.”

“That’s OK. He doesn’t have to be here.”

She opened the door a crack, and the door frame moved, almost imperceptibly. Yet it didn’t really move. The world seemed to shift, and I felt off balance for a moment. The door opened a bit wider, and then I saw them: cockroaches, thousands of them, scurrying along the top of the door to get out of the way.

The door opened the rest of the way. The apartment was dark, and it took a moment to appreciate what was inside. No floor was visible, only a layer of dirty papers, food wrappers, and urine-stained rags. A rottweiler bolted out of the back to see what was going on. He jumped over a pile of dirty clothes—at least they looked like clothes. From the edge of the door, the massive pile of junk rose precipitously to the ceiling, like a giant sea wave. It could have been part of a landfill: papers, boxes, shopping carts, paper bags, dirty clothing, lamps—anything that could be easily collected from the street or fished out of a Dumpster. It was one solid wall of trash 20 feet deep, all the way to the back of the apartment. There must have been windows on the far wall, but they were darkened by the broken fans, boxes, and clothing covering them.

Inside the condo the sweet, pungent odor of insects and rotting food enveloped us. Susan had instructed me to wear old clothes that I could throw out afterward. I was grateful for the advice but wished I’d also had a face mask—the heavy-duty kind.

I could feel the cockroaches surrounding me as I stepped in. The walls were coated with their brown dung, and occasionally one dropped from the ceiling onto the piles of debris below. I walked farther in to get a better look at the kitchen, or what I thought was the kitchen. It was impossible to tell, since everything was covered with bags. Food, mostly old and rotting, empty but unwashed tuna cans, and colorful coupons adorned the room. There was a path into the kitchen, though it was atop six inches of trash on the floor.

I was afraid to touch anything. I suddenly felt a great deal of sympathy for all the people I’d met with contamination phobias: This must be what it feels like, I thought.

Susan, the court-appointed guardian of Edith, who had struggled to open the door for us, had obtained a judge’s order for a “heavy-duty cleaning” because she believed that Edith’s health and safety were in danger, and no more moderate measure had succeeded in improving the horrific living conditions in the condo. Edith wasn’t responsible for these conditions. It was all her brother Daniel’s doing. And Daniel didn’t see anything wrong with the place. “All of this stuff we can use,” he insisted. “There is nothing wrong with our home.”

What brain circuitry may be involved in the development of hoarding? Researchers at the University of Iowa compared brain-damaged patients who began abnormally collecting things following their injuries to brain-damaged patients who did not collect. All of the abnormal collectors had damage in the middle of the front portion of the frontal lobes, while the noncollecting patients’ damage was scattered throughout the brain. The prefrontal region of the brain is responsible for goal-directed behavior, planning, organization, and decision making—all activities that represent challenges for people who hoard.

Brain scan studies provide additional information. Sanjaya Saxena, director of the Obsessive-Compulsive Disorders Program at the University of California at San Diego, found lower metabolism (an indication of the level of activity in that portion of the brain) among hoarders in regions of the brain roughly corresponding to those identified in the University of Iowa study. In particular, hoarders had lower metabolic rates in the anterior cingulate cortex, one region responsible for motivation, focused attention, error detection, and decision making.