Psychiatric Vs. Neurological: Can the Brain Tell?

A search for brain differences between psychiatric and neurological disorders

Posted Dec 02, 2015

My last posting explored the question of whether or not autism should be considered a psychiatric disorder versus belonging to some other category (developmental, neurological, etc.).  Right after the post came out, an interesting study appeared in the latest issue of the British Journal of Psychiatry.  The study ambitiously tried to see whether or not they could find differences between disorders classically defined as being psychiatric versus neurological based on brain anatomy.

In an effort to give equal weight to multiple different disorders, the authors chose 7 studies each on a variety of different conditions.  Neurological disorders included epilepsy, Parkinson’s disease, multiple sclerosis, and types of dementia including Alzheimer’s disease.  Psychiatric disorders included things like depression, schizophrenia, PTSD, ADHD, and yes, autism.  In total, 168 different studies that included nearly 4000 patients and controls each, were included.   All of these studies used anatomic magnetic resonance imaging (MRI) to compare the size of specific regions of the brain between patients and controls.  They also looked at brain networks, that is, multiple brain regions that coordinate activity to perform different tasks.

They key question was whether disorders classified as neurological would implicate the same brain regions and networks as psychiatric disorders or whether each category of illness would involve different areas.

The answer was a bit of both.  Certainly, both types of disorders were found to be associated with measurable differences in brain anatomy.   Further, some areas such as the hippocampus (a structure involved in memory and emotion processing) was often found to differ in size compared to controls in people with both neurological and psychiatric disorders.  At the same time, however, there was evidence that neurological disorders were more likely to predict “abnormalities” in brain regions and networks that were different than the ones found for studies of psychiatric disorders.

Some of these differences made sense such as psychiatric disorders implicating areas of the frontal lobe more than neurological disorders.  Others, however, were more surprising such as psychiatric disorders being more associated with brain networks involved in processing visual information.  Overall, it was difficult for the authors to come up with a coherent “theme” to summarize the nature of psychiatric versus neurological disorders with regards to brain anatomy, other than to say that some differences were found.

The way that this study has been used and covered has also been interesting.  Particularly among the more anti-psychiatry crowd, there has been the implication that the study supports the assertion that psychiatric disorders aren’t real.  However, the authors clearly state that “we found that both types of disorders were associated with widespread alterations in cortical and subcortical areas.”

There has been some discussion that perhaps the fields of neurology and psychiatry should be collapsed, as both specialties lay claim to the same organ.  It is hard to say how this study should be used in that debate, as certainly you wouldn’t subdivide orthopedics based on arm bones versus leg bones. Nevertheless, there may be other more legitimate reasons to keep the specialties distinct at least for now, and the brain is certainly complex enough to have lots of people looking out to keep it as healthy as possible.     

@copyright by David Rettew, MD

David Rettew is author of Child Temperament: New Thinking About the Boundary Between Traits and Illness and a child psychiatrist in the psychiatry and pediatrics departments at the University of Vermont College of Medicine.

Follow him at @PediPsych and like PediPsych on Facebook.