Mental Illness Defined as Disruption in Neural Circuits

It has become an NIMH mantra to describe mental disorders as brain disorders. What does this mean? Is it accurate to group schizophrenia, depression, and ADHD together with Alzheimer’s disease, Parkinson’s disease, and Huntington’s disease? Is a neurologic approach to mental disorders helpful or does this focus on the brain lead to less attention to the mind?

First, mental disorders appear to be disorders of brain circuits, in contrast to classical neurological disorders in which focal lesions are apparent. By analogy, heart disease can involve arrhythmias or infarction (death) of heart muscle. Both can be fatal, but the arrhythmia may not have a demonstrable lesion. In past decades, there was little hope of finding abnormal brain circuitry beyond the coarse approach of an EEG, which revealed little detail about regional cortical function. With the advent of imaging techniques like PET, fMRI, MEG, and high resolution EEG, we can map the broad range of cortical function with high spatial and temporal resolution. For the first time, we can study the mind via the brain. Mapping patterns of cortical activity reveals mechanisms of mental function that are just not apparent by observing behavior….

By Thomas Insel, M.D.
NIMH Director

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