This
article appeared in Aging Today, January/February 1998, copyright American
Society on Aging, 1998. It appeared in the newspaper's Research Today section,
aupported by a grant from the AARP Andrus
Foundation.
DEPRESSION'S LINK TO BRAIN DISORDERS
Biology may play a key role in geriatric depression, according to Ira R. Katz, professor of psychiatry at the University of Pennsylvania, Philadelphia and principal investigator of "Late Life Depression: Psychiatric Medical Comorbidity," a National Institute of Mental Health (NIMH) study. He and other researchers wrote about late-life depression in the Summer 1997 issue of The Decade of the Brain, a publication of the National Alliance for the Mentally Ill.
Recent findings implicate vascular disease, particularly strokes, in the course of geriatric depression. Depression often coincides with vascular disorders, especially when accompanied by lesions in the basal ganglia and prefrontal areas of the brain, according to a recent statement by an NIMH panel on late-life depression. The panel members wrote that "dysfunction of frontal brain systems is a possible contributing factor in depression in late life."
SEMINAL STUDIES
The NIMH panel cited a "seminal series of research studies" by Robert Robinson, now chairperson of psychiatry at the University of Iowa, Iowa City. The research revealed that the presence or absence of depression after a stroke was related more to the location of the brain lesions than to the extent of disability, said Katz. In particular, Robinson found that patients whose strokes occurred on the left side of the brain--and near its front--were more likely to be depressed than other stroke patients, according to Katz.
By suggesting that depression can result from damage to specific neural circuits, the finding has provoked debate in the field, Katz said. "Everyone agrees that people who have had a stroke are at increased risk for depression as opposed to healthy elders. The controversy is whether the anatomic correlations are really what are important in predicting depression," he explained. Other scientists believe that the overall degree of disability that older stroke patients experience is more indicative of future episodes of depression than where brain lesions occur.
More recently, research using magnetic resonance imaging of the brain has demonstrated that geriatric depression--especially when the initial onset is late in life--is associated with the presence of subclinical or "silent" strokes, so called because they can happen without the individual realizing it. Resulting lesions involving very small blood vessels are located in subcortical or "white matter" areas of the brain. Several separate studies, especially those by researchers at Cornell University Medical Center, Duke University and the University of Pennsylvania, have consistently found associations between such subclinical strokes and depression, Katz said.
What's more, lesions caused by subclinical strokes "occur predominantly in patients with risk factors for cerebrovascular disease, including hypertension, diabetes, cardiac disease and peripheral vascular disease," Katz wrote. "By controlling the risk factors for these conditions, such as cholesterol levels and smoking habits, people might not only live longer but also have a better quality of life," he said.
In addition, Katz noted, other research suggests that depression in Alzheimer's and Parkinson's disease patients is "very responsive to treatment," even though it results from neurodegeneration. Promising research in Alzheimer's patients has suggested that depression is linked to the decline of norepinephrine neurons in the brain stem and to the loss of the neurotransmitter serotonin, a chemical secreted by neuron cells in the brain that investigators believe also plays a role in depression among Parkinson's patients.