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THE BRAIN'S ROLE IN PSYCHIATRIC DISORDERS
Does brain dysfunction cause psychiatric disorders?
Kenneth Kendler, one of the most influential and prolific psychiatric researchers and historians of our time, recently published two articles examining the role of the brain in psychiatric disorders: “A history of metaphorical brain talk in psychiatry” and “Are psychiatric disorders brain diseases? A new look at an old question.” The papers were published in the journals Molecular Psychiatry and JAMA Psychiatry, respectively.
Kendler's View:
Kendler argues that declarations that psychiatric disorders are brain diseases may be misleading: Such pronouncements suggest that abnormalities in the brain directly cause psychiatric disorders., but evidence that this is true is lacking.
Kendler defines metaphorical brain talk “as describing the disturbed mental processes in psychiatric illness in terms of brain function in ways that appear to be explanatory but actually have little to no explanatory power.” After reviewing pertinent literature since 1784 in which psychiatric disorders are declared to be brain diseases., he posits that one reason psychiatrists support the concept is that they, as medical specialists, are in search of a broken organ responsible for the disorders they treat.
Other medical specialties often focus on abnormalities of a specific organ, for example, ophthalmology the eye, cardiologists the heart, gynecologists the uterus and ovaries. Taking an example from the late twentieth century, Kendler points to The Broken Brain by "a leading biological psychiatrist, Nancy Andreasen" as "a widely-cited book whose title was a paradigmatic example of metaphorical brain talk.”
Some arguments supporting the broken brain concept are weak—for instance, the conclusion by some that depression is a disorder of serotonin imbalance based on serotoninergic mechanisms associated with certain antidepressants. Kendler observes, "trying to clarify disease etiology through the mechanism of action of pharmacologic treatments is deeply problematic as illustrated by the now common phrase: ‘headache is not an aspirin-deficiency disease.’”
On the other hand, there is evidence that at least some psychiatric disorders may result directly from primary brain abnormalities. Kendler points to schizophrenia; psychiatric geneticists have shown elevations in gene variants in specific brain regions and neurons associated with the illness. The location of the genetic alterations, Kendler argues, suggests that schizophrenia may be caused by brain abnormalities.
Although there have been significant advances in neuroscience leading to better understanding brain and behavior, such advances have not yet led to elucidating brain abnormalities as the cause of all psychiatric disorders, Kendler notes.
The View of the Authors
In our book Demystifying Psychiatry, we define psychiatry as “the medical specialty that deals with disorders affecting the human mind and behavior.” Based on Joseph LeDoux’s work, we think of the mind “as brain systems underlying cognition (thinking), emotions (meaning), and motivation (goals).”
Most would agree that cognition, emotion, motivation, and behavior result from brain activity. Although psychiatric symptoms result from perturbations in brain systems underlying cognition, emotions, and motivation, this does not mean that the primary causes of these perturbations reside in the brain.
For example, inflammatory processes in the body may be causally related to subtypes of depression and other psychiatric disorders. Although the primary location of the inflammation may be outside the brain, abnormalities related to inflammation may involve brain systems that lead to manifestation of depressive symptoms. In such a case, the psychiatric disorder is a result of inflammatory processes that secondarily influence brain function, suggesting that the brain is involved in the behavioral manifestation of the disorder, but the primary pathology originates outside the brain. It is important to note, however, that the brain can generate its own inflammatory signaling, so even dysfunction that originates in the body can set off complex body-brain interactions resulting in psychiatric symptoms and disorders.
We agree with Kendler that oversimplification and metaphorical brain talk are counterproductive. We believe that all psychiatric disorders manifest their symptoms via brain activity. However, it is possible that the underlying causal pathophysiology of some psychiatric disorders does not reside in the brain. Other disorders, such as schizophrenia, may be a result of direct brain dysfunction.
Over the last decade, major progress has been made in brain research relevant to psychiatry. Investigations of neural circuits underlying cognition, emotion, and motivation are advancing our knowledge of the mind. We are strong believers that, with the help of leaders like Dr. Kendler, the research will lead to a more complete understanding of psychiatric symptoms and syndromes.
As we learn more about the biology underlying symptoms, better diagnostic criteria and mechanistic understanding will be developed. Such knowledge should lead to better treatments and, ideally, to approaches that prevent the development of the disorders.
Psychiatry focuses on understanding abnormal human behavior. We have a long way to go, but the journey is both challenging and exciting.
This post was co-written by Eugene Rubin, MD, PhD, and Charles Zorumski, MD.
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