ndividuals who suffer from severe depression have more nerve cells in the part of the brain that controls emotion, researchers at UT Southwestern Medical Center at Dallas have found.
Studies of postmortem brains of patients diagnosed with major depressive disorder (MDD) showed a 31 percent greater than average number of nerve cells in the portion of the thalamus involved with emotional regulation. Researchers also discovered that this portion of the thalamus is physically larger than normal in people with MDD. Located in the center of the brain, the thalamus is involved with many different brain functions, including relaying information from other parts of the brain to the cerebral cortex.
The findings, published in today's issue of The American Journal of Psychiatry, are the first to directly link a psychiatric disorder with an increase in total regional nerve cells, said Dr. Dwight German, professor of psychiatry at UT Southwestern.
"This supports the hypothesis that structural abnormalities in the brain are responsible for depression," he said. "Often people don't understand why mentally ill people behave in odd ways. They may think they have a weak will or were brought up in some unusual way.
"But if their brains are different, they're going to behave differently. Depression is an emotional disorder. So it makes sense that the part of the brain that is involved in emotional regulation is physically different."
I find it curious that an emotional disorder would seemingly need such a large change in the size of a part of the brain in order for the disorder to manifest. Small changes in enormous computer programs can lead to large malfunctions. Yet at least with major depression incredibly small changes are apparently not sufficient to cause it in most sufferers of depression.
Note, however, that sufferers of bipolar depression do not have an increase in the size of the mediodorsal and anteroventral/anteromedial areas of the thalamus. So then is there an abnormality in the size of some other part of the brain of bipolars waiting to be discovered?
Researchers from UT Southwestern, working with a team from Texas A&M University System Health Science Center, used special computer-imaging systems to meticulously count the number of nerve cells in the thalamus.
Results showed an increase of 37 percent and 26 percent, respectively, in the number of nerve cells in the mediodorsal and anteroventral/anteromedial areas of the thalamus in subjects with MDD when compared with similar cells in those with no psychiatric problems. The number of nerve cells in subjects with bipolar disorder and schizophrenia was normal.
Researchers also found that the size of the affected areas of the thalamus in subjects with MDD was 16 percent larger than those in the other groups.
"The thalamus is often referred to as the secretary of the cerebral cortex – the part of the brain that controls all kinds of important functions such as seeing, talking, moving, thinking and memory," Dr. German said. "Most everything that goes into the cortex has to go through the thalamus first.
"The thalamus also contains cells that are not involved with emotion. Our studies found these portions of the thalamus to be perfectly normal. But the ones that are involved in emotion are the ones that were abnormal."
Researchers also looked at the effect of antidepressant medications on the number of nerve cells and found no significant difference among any of the subject groups – whether they had taken antidepressants or not – reinforcing the belief that abnormalities in brain development are responsible for depression.
Does this report suggest any avenues for the development of therapeutic treatments? Could a drug be developed that would inhibit some of the neurons in the mediodorsal and anteroventral/anteromedial areas of the thalamus? Would such a drug reduce the symptoms of depression? It will be interesting to see what develops from this report.
|Share |||Randall Parker, 2004 July 06 06:25 PM Brain Disorders|