Images of Obsession; the Peculiar Symptoms of Obsessive-Compulsive Disorder Appear to Be Linked to a Mismatch in the Brain's Metabolic Activity
Bower, Bruce, Science News
Images of Obsession
Every day, a young woman shakesher clothes for a half hour and washes herself for up to six hours, haunted by the thought that germs might infect her with a deadly disease. A man cannot prevent himself from driving back to check every place on the road where he has hit a bump, because thoughts that he has run someone over torment him at every turn. Another man stops cooking for fear he will poison his wife and refuses to use electrical appliances because he worries about causing a fire.
These people illustrate some of thesymptoms of obsessive-compulsive disorder, a strange brew of recurrent ideas and impulses that are often experienced as repugnant (obsessions) mixed with ritualistic, seemingly senseless behaviors aimed at preventing harm and warding off anxiety (compulsions). An estimated 2 percent of the adult population in the United States suffers from obsessive-compulsive disorder at some time in their lives, and one-third of them develop the disorder during childhood.
French physician and psychologistPierre Janet described obsessive-compulsive disorder, using the term "psychasthenia,' in a classic 1903 publication. Not long afterward, Sigmund Freud conceived of obsessions and compulsions in his patients as complex psychological defenses used to deal with unconscious sexual and aggressive conflicts.
In contrast with this long history ofclinical observation, little is known about what parts of the brain help to produce the disorder's bizarre thoughts and acts. But that is beginning to change.
In the March ARCHIVES OF GENERALPSYCHIATRY, scientists at the University of California at Los Angeles School of Medicine suggest that there is an imbalance in the energy-conversion rates of two structures in the frontal lobes of obsessive-compulsives. The two brain regions normally work together to help channel and contron incoming sensations and perceptions.
While this metabolic mismatch accompaniesobsessive-compulsive symptoms, says psychiatrist and project director Lewis R. Baxter Jr., it is not necessarily a cause of the disorder.
The new report is based on positronemission tomography (PET) scans of 14 obsessive-compulsives, 14 individuals with severe depression and 14 controls with no psychiatric diagnoses. PET-scanning devices transform quantitative measures of metabolic activity throughout the brain into color-coded pictures. As in many other PET experiments, a radioactively labeled glucose compound was used to gauge tissue reponses, since glucose is a prime energy source in the brain.
Compared with depressed and controlsubjects, obsessive-compulsives had significantly increased glucose metabolism in a frontal lobe region on the left hemisphere, known as the left orbital gyrus. The right hemisphere's corresponding orbital gyrus showed no substantial jumps in activity. In addition, the metabolic rate in the left orbital gyrus, relative to that of the entire left hemisphere, was markedly elevated among obsessive-compulsives, and stayed high even among eight subjects whose symptoms eased after treatment within an antidepressant drug.
Since all of the obsessive-compulsivesubjects were right-handed, says Baxter, it appears that activity in the dominant-hemisphere orbital gyrus is most affected. A left-hander with the diagnosis was recently given a PET scan by the UCLA researchers, and an increased metabolic rate in the right orbital gyrus was observed.
Animal studies, notes Baxter, indicatethat the orbital gyri are involved in directing attention toward specific objects. Damage to this area can cause animals to engage in repetitive behaviors.
Two other frontal-lobe structures, thecaudate nuclei, located on opposing hemispheres, also displayed significant jumps in metabolic rate relative to overall hemisphere activity, but only among obsessive-compulsives who improved after drug treatment. Before treatment, the ratio of caudate activity to hemisphere activity was within the normal range for obsessive-compulsive subjects, and it did not increase among those whose symptoms did not improve. …