December 1, 2019
As advances in neurobiology and genetics reveal complex associations between brain structure, function, and the symptoms of mental illness, there have been renewed calls to reposition mental illness as disease of the nervous system. This is highlighted in public statements by prominent figures in American psychiatry, such as Thomas Insel's assertion that mental illness is brain disease and Eric Kandel's proposal to merge psychiatry with neurology...
I argue that these proposals to reclassify mental illness as neurological disease are based on a basic category error and that the distinction between psychiatry and neurology is not an arbitrary one...
Neurological diseases are, by definition, diseases of the central and peripheral nervous system, and they can generally be identified on the basis of objective medical testing, such as electroencephalography for epilepsy and magnetic resonance imaging for a brain tumor...
In contrast, mental or psychiatric illness is characterized by a clinically significant disturbance in an individual's thoughts, feelings, or behaviors. The Diagnostic and Statistical Manual of Mental Disorders is theoretically neutral on the cause of mental disorders, and, despite claims to the contrary by antipsychiatrists, organized American psychiatry has never officially defined mental illness as "chemical imbalance" or brain disease (see Pies, 2019).
While many advances have been made in the realms of neuroscience and genetics that aid our understanding of mental illness, there remains not a single identifiable biomarker for any mental disorder. Historically, mental disorders have been considered functional diseases, due to their impairment of functioning, rather than structural diseases, which are associated with known biological abnormalities.