Researchers provide no definitive explanation of this behavior, but it seems rather intuitive. Extensive studies on the effects of solitary confinement of humans has shown similar symptoms of mental disorders -- with many considering the punishment to be a form of psychological torture.
While this study focuses on dogs that are properly stimulated throughout the day, the effects of isolation for the thousands of dogs kept in rescue center kennels is likely much more profound. A paper released by the Stafford Animal Shelter in Montana describes a mental illness, known as "kennel crazy" or "kennelitis" in canines left too long in confinement:
"Symptoms of this stress-induced canine compulsive behavior disorder can include spinning and jumping in the kennel, chewing incessantly, and jumping and pulling excessively if on a lead... Other more depression-like symptoms may include self-mutilation, lack of appetite and lethargy."
The shelter says that in some cases, the effects of this illness can render dogs unadoptable. Sadly though, overcrowded animal shelters in the United States often don't have the time or resources to provide dogs with much time, if any at all, outside of their kennels -- leading to mental suffering that will go unresolved for many of the animals that fail to find a home.