Drawing the Line Between Neurological and Psychiatric Disorders

By: Kate Leinenweber

Image credit: The Hartman Center for Functional Neurology

This past September, I attended a thought-provoking talk at Arizona State University featuring Dr. James Dennert and Dr. Jason Robert. The two of them spent the time debating and engaging the audience on a central topic: what is the difference between a neurological and psychiatric disorder? Where can we actually draw that line? How do we determine what issues we send people to a neurologist for, and what issues we send people to a psychiatrist or therapist for? When did we decide which diseases belonged where?

“Mental Illnesses are Illnesses Like Any Other”

Dr. Dennert, one of the speakers, spent 40 years as a psychiatrist before pursuing his doctorate. His thesis investigated the common saying in psychiatry that “mental illnesses are illnesses like any other.” The phrase asserts that mental disorders are physical disorders of the brain and should be treated in the same way as any other physical illness. This saying promotes the idea that there is a neurobiological base behind mental disorders, which could help reduce the social stigma surrounding them (Malla, 2015).

If psychological and psychiatric disorders were considered as physical disorders of the brain, the same way that neurological disorders are, then they would be less likely to be stigmatized as issues people can simply “get over” by focusing better, worrying less, or being less sad. This perspective is meant to promote the social acceptance of psychiatric disorders, helping patients and their families be more open to diagnosis and treatment. Surprisingly, there are arguments both for and against this perception, whereas I had originally assumed most therapists would support this idea as a way to reduce social stigma surrounding mental illness. Dr. Dennert challenged my assumption by arguing that mental illnesses are not illnesses like any other. He emphasized that mental illnesses possess unique pathologies, modes of symptom production, and treatment methods that distinguish them from other physical disorders.

Physical vs. Mental Illness

Dr. Dennert’s reasoning for this conclusion follows the path from the “cause” of a disease – a specific bodily or cellular dysfunction – to the symptoms that you would observe in a person. For instance, diabetes is a result of the body’s inability to produce enough insulin, impairing its ability to regulate blood glucose levels. The disease stems from a clear abnormal pathology in a specific organ, the pancreas, and the symptoms are direct consequences of that dysfunction (Dennert, 2024, p. 25). In contrast, Dr. Dennert argued that the link between cause and symptoms in mental illness is far less concrete. While dysfunctional neural activity or imbalances in neurotransmitters lead to changes in behavior, it is hard to determine exactly why and how that process occurs. Unlike physical illnesses, mental disorders lack a definitive connection between the brain’s physical state and the contents of our thoughts, emotions, or behaviors.

As someone who primarily researches molecular biology and neuroscience, hearing Dr. Dennert’s argument sparked my curiosity. Why do we define neurological and psychiatric disorders the way we do, and why do we sometimes struggle to draw the line between them? Current research on the origins of these disorders tends to focus a lot on the genetic basis of disease, while others focus on our environment, or tracing the path from cause to symptom. However, the way our bodies work is a combination of all these approaches, and possibly more that we haven’t discovered yet. So, what is the best way to go about characterizing them?

I initially believed that psychiatric disorders should be observed on the same basis that neurological disorders are: as conditions stemming from some protein neurotransmitter dysfunction in the brain, something that can be characterized by a physical marker or a dysfunctional gene variant. The saying that “mental illnesses are illnesses like any other” is common for a reason – we want to strive for parity in how we address neurological and psychiatric disorders. Not to mention, the human body doesn’t just divide diseases into neat categories. We can try to box things into categories to make disorders easier to understand, but nothing about our evolution and the different disorders that have come from it is naturally ordered or easy to understand.

And yet, Dr. Dennert’s point still stands: there is a difference. At the very least, this difference is prominent enough that we created these two broad categories for brain diseases to fall into – diseases that affect our psyche, and diseases that affect our nervous system. If we are going to continue to differentiate between them, however, we need to have a good reason besides tradition behind it. We need to think critically about common beliefs, and reassess what frameworks we use in psychology and medicine. It might then lead us to develop new therapeutic and physical treatments, and allow for a better characterization of these diseases. This question prompted me to examine more closely how and why we categorize neurological and psychiatric conditions the way we do.

So What is the Difference?

In the medical field, there is a relatively clear consensus on where we draw the line between neurological and psychiatric disorders, rooted in whether the dysfunction primarily affects the nervous system or whether it affects mood and behavior. Neurological disorders are primarily defined by dysfunction in the nervous system, which includes the brain, spinal cord, and nerves (Galinato, 2018). Conditions like Alzheimer’s disease and Parkinson’s disease fall under this category because the diseases are primarily characterized by neuronal degeneration and death. Similarly, epilepsy is classified as neurological because its symptoms arise from abnormal electrical signaling between neurons. Psychiatric disorders, on the other hand, are primarily defined by abnormalities in mood, behavior, and emotional state. For instance, depression is characterized by changes in emotions, feelings of emptiness, and unusual sleeping and eating patterns. Anxiety is characterized by restlessness, persistent anxious thoughts, and difficulty with decision making. While many psychiatric disorders may present with physical symptoms, their hallmark is their impact on mental states, thus it is harder to trace their neurology.

Of course, the way we categorize these disorders is not the end all be all, and neurological and psychiatric disorders tend to overlap greatly. Many neurological disorders  affect mood and behavior, and there are often higher rates of psychiatric issues in people with other neurological disorders. For example, Alzheimer’s disease is characterized by the accumulation of amyloid plaques and tau tangles in the brain, but it is also primarily recognized when people with the disorder experience unexpected changes in memory and emotional regulation. People with Alzheimer’s, Parkinson’s, and epilepsy, which are all defined as neurological disorders, are often impacted by depression, exemplifying how suffering from a neurological disorder can affect a person’s mental health.

In recent years, neuropsychiatry has gained prominence as a field that bridges the gap between neurology and psychiatry. This approach is based on the approach that neurological and psychiatric disorders, though intrinsically different, overlap in many significant ways. Many disorders can benefit from a combination of treatments from both areas. For example, many medications traditionally used for psychiatric disorders, like SSRIs and antipsychotics, can also affect neurotransmitters, and have demonstrated effectiveness in reducing symptoms of neurological disorders such as epilepsy or Huntington’s disease (Taslim, 2024). Additionally, ongoing research into the genetic basis of psychiatric disorders is uncovering physical mechanisms that could lead to improved treatments.

The brain is a unique and complex organ which serves as the center of our behavior and thought while still being a physical organ that is susceptible to dysfunction like any other. While debates about the conceptual distinctions between neurological and psychiatric disorders are useful, it’s important to realize that our categorization of these disorders are just our way of making sense of the complicated system that is the human body. Our knowledge will continue to evolve as we make advances in our research and understanding of the brain and mind. As the boundaries between neurological and psychiatric conditions continue to blur, we can learn to view disorders of the brain on a spectrum rather than boxing them into discrete categories. By viewing brain disorders as interconnected rather than separate, we can develop more effective, holistic treatments for a wide range of conditions, ensuring that patients receive comprehensive care regardless of the traditional classification of their disorder.

References: 

Baker, M. G., Kale, R., & Menken, M. (2002). The wall between neurology and psychiatry. BMJ (Clinical research ed.), 324(7352), 1468–1469. https://doi.org/10.1136/bmj.324.7352.1468

Brain and Spine Specialists. (2024, March 21). Neurological vs Psychological - A Closer Look | Brain And Spine Specialists. https://brainandspinecenterllc.com/2024/03/21/neurological-vs-psychological-a-closer-look/.

David, A. S., & Nicholson, T. (2015). Are neurological and psychiatric disorders different?. The British journal of psychiatry : the journal of mental science, 207(5), 373–374. https://doi.org/10.1192/bjp.bp.114.158550

Dennert, J.W. (2024). "Mental Illnesses Are Illnesses Like Any Other": An Inquiry and Critique. ASU Electronic Theses and Dissertations. https://hdl.handle.net/2286/R.2.N.193427.

Hartman, J. (2023, August 28). What Are the Common Therapies Used in Brain Injury Treatment?. The Hartman Center for Functional Neurology. https://thehartmancenter.com/what-are-the-common-therapies-used-in-brain-injury-treatment/.

Malla, A., Joober, R., & Garcia, A. (2015). "Mental illness is like any other medical illness": a critical examination of the statement and its impact on patient care and society. Journal of psychiatry & neuroscience : JPN, 40(3), 147–150. https://doi.org/10.1503/jpn.150099

Galinato, M. (2018). What Is the Difference Between Neurological and Psychiatric Disorders? Brainfacts.org. https://www.brainfacts.org/diseases-and-disorders/mental-health/2018/what-is-the-difference-between-neurological-and-psychiatric-disorders-070618.

Pescosolido, B. A., Martin, J. K., Long, J. S., Medina, T. R., Phelan, J. C., & Link, B. G. (2010). “A Disease Like Any Other”? A Decade of Change in Public Reactions to Schizophrenia, Depression, and Alcohol Dependence. American Journal of Psychiatry, 167(11), 1321–1330. https://doi.org/10.1176/appi.ajp.2010.09121743

Taslim, S., Shadmani, S., Saleem, A. R., Kumar, A., Brahma, F., Blank, N., Bashir, M. A., Ansari, D., Kumari, K., Tanveer, M., Varrassi, G., Kumar, S., & Raj, A. (2024). Neuropsychiatric Disorders: Bridging the Gap Between Neurology and Psychiatry. Cureus, 16(1), e51655. https://doi.org/10.7759/cureus.51655.