|By Tré LaRosa
Terms in medicine and science can often be challenging to understand. The fields related to the mind and nervous are no different. Neuroscience, neurology, psychology, psychiatry — you’ve probably heard all of these terms before but do you know how they differ?
Psychology and psychiatry primarily deal with the mind; psychology tends to be more research-based since it means the study of the mind, while psychiatry tends to focus on the treatment of maladies related to the mind, or psychiatry disorders since psychiatry is the branch of medicine focused on the mind. As for the nervous system, the divergence in definition is similar: neuroscience is the study of the nervous system while neurology is the branch of medicine that deals with neurological conditions. The differences seem distinct but in reality, the distinctions tend to be much muddier. Plenty of psychologists end up spending their entire career helping people with mental disorders and plenty of psychiatrists spend their careers researching. In terms of the nervous system, it’s probably fair to say that all neurologists are to some degree neuroscientists, but not all neuroscientists are neurologists. Neurologists must have a strong understanding of the nervous system, but neuroscientists aren’t typically involved in the treatment of neurological conditions. This might be pedantic, but not all neurologists are actively involved in research on the nervous system, so in that case, not all neurologists are technically neuroscientists.
In this blog, we’ll talk about the philosophical approaches of the different fields and why the recent history of their convergence is a good thing for patients with either mental or neurological conditions or both.
It might seem strange or like a pointless exercise to define these different fields with such precise language but the phrasing of the field often influences the philosophical approaches to treating and researching the mind. Further, the fields don’t always align in their approaches. It’s important we understand why and why they should continue converging.
Neurological and psychiatric disorders: How do they differ? Does one cause the other?
Before delving more deeply into the fields themselves, it’s important to understand why they exist independently at all. It’s common to divide conditions of the brain and conditions of the mind into two distinct entities — psychiatric (or mental) disorders and neurological disorders. Some common psychiatric or mental disorders include depression, anxiety, bipolar disorder, schizophrenia, and borderline personality disorder. Neurological disorders include amyotrophic lateral sclerosis (ALS, also known as Lou Gehrig’s disease), epilepsy, Alzheimer’s (and other dementias), Parkinson’s disease, stroke, multiple sclerosis, spinal muscular atrophy, and many others. The challenge, however, is that some psychiatric diseases have neurological impacts — as in, brain abnormalities that have been linked with specific psychiatric diseases — while some neurological disorders negatively affect the minds and behavior of patients. The crux of the debate is that if the mind — healthy or otherwise — is emergent from biological processes in the brain, then can any disease that affects the mind be separated from the functioning of the brain? This summary sheds a better light on the conversation: It’s not reasonable to think that any one specialist can best understand the brain and its functioning, the mind and its functioning, and how to treat any dysfunction in both.
When considering how mental and neurological conditions differ, another question arises: Is one the result of the other, do they arise independently, or is the answer more complex? (Simple rule-of-thumb: Pretty much every answer in science is more complex than a simple binary.) This question of comorbidities is a straight-forward example of the classic research mantra: Correlation does not imply causation.
Comorbidities: A classic example of correlation vs causation
A major challenge in medicine and research is understanding when two variables are correlated compared to when one variable is directly or indirectly affecting the other variable — if two variables are correlated, when one changes, the other changes in either a positive or negative fashion. Variables can be tightly correlated — when one shifts by 10%, the other shifts by around 10% as well. Or variables can be loosely correlated — when one variable shifts by 10%, the other shifts to a much lesser extent, like 2%, or much greater extent, like 40%. In either case, when two variables are correlated, the reason there isn’t always causation is because they both variables can be caused by something else, which is why they shift similarly. Sometimes, it’s purely coincidental! The example Khan Academy uses is that more ice cream and air conditioners are sold in the warmer months, but you wouldn’t expect that if ice cream parlors started selling more ice cream, there would be a direct increase in air conditioner sales. Instead, it’s more likely that people are more likely to buy ice cream when it’s hotter and more people are likely to need air conditioners when it’s hot out. A useful rule-of-thumb to gauge situations where you’re trying to decipher correlation vs causation is to ask yourself what is the most simple, rational explanation to describe a relationship. In philosophical parlance, this is known as a “heuristic” (rule-of-thumb), and specifically, “Occam’s razor.” Of course this is not always the case — which is why it’s crucial to understand how to use science to control for confounding variables and discern a true causative relationship before making definitive claims.
Comorbidities are perfect examples of the challenge of discerning correlation vs causation in the clinic and the lab. Since psychiatric conditions affect the mind, which we know is produced from biological processes in the brain, it’s tempting to call psychiatric disorders neurological disorders. This approach doesn’t always make sense and can actually flatten the way both types of conditions are researched and treated. Comorbidities are associated with worse outcomes and make patients more complex cases. A patient with both depression and multiple sclerosis might have developed both of those conditions independently. This would mean the depression did not cause the MS and the MS did not cause the depression. This patient’s brain might still demonstrate hallmarks of both conditions — but both of these conditions would need to be treated differently despite their being concurrent abnormalities in the brain. With one condition resulting in more prominently physical symptoms and one causing more mental symptoms, it’s crucial this patient sees specialists that can treat both as best as possible. It’s helpful to know if certain conditions are more likely to result in other conditions — especially when they have a profound impact on somebody’s quality of life — but discerning causation can take time, and time is of the essence when treating patients.
For other articles that dive deeper into correlation vs causation, consider reading the “Considering the Unseen Links to Alzheimer’s” series where we looked into the evidence that suggests air pollution, gingivitis, and diet are associated with increased risk (and potentially causative) for Alzheimer’s.
How do the fields differ and overlap?
Neuroscientists work to better understand the nervous system. Some neuroscientists are specifically interested in understanding neurological conditions, or disorders that affect the nervous system, but not every researcher is primarily researching conditions. Neuroscientists are often interested in increasing our understanding of the broader implications of the nervous system. Let’s take a look at some of the articles published in the most recent issue of Nature Neuroscience.
- Motor learning drives dynamic patterns of intermittent myelination on learning-activated axons
- Complementary task representations in hippocampus and prefrontal cortex for generalizing the structure of problems
- Thalamus-driven functional populations in frontal cortex support decision-making
In this issue, there were a total of six articles. Of those six articles, only one was related to a disorder. The other five were related to newfound insights in typical functioning of the nervous system. Their revelations might have implications for neurological disorders — for example, the first article listed above could very well advance our understanding of multiple sclerosis since MS results in damage to the myelin sheath, the insulating material that surrounds nerve fibers,a crucial material that accelerates how quickly impulses are carried through nerves.
Conversely, in the most recent issue of Nature Reviews Neurology, nearly every piece of written material — articles, comments, briefs, highlights, news, views, reviews, and perspectives — listed a neurological condition in its title. Again, research within neurology that is not specific to neurological disorders exists, but those are the exception to the rule. It’s difficult to assign exact, clear boundaries for what is within a field. Fields share overlap and influence each other.
The overlaps between the fields seen above in neurology and neuroscience also exist in the fields that study the mind.
The influential journal — also part of the Nature portfolio — Molecular Psychiatry publishes work aimed at shedding light at the biological mechanisms — the neural processes, the parts of the brain, et cetera — underlying psychiatric disorders and how to treat them. Most of the published research is at the junction of preclinical and clinical research. Here’s one example of a recent article published in the journal: Psychosocial functioning in the balance between autism and psychosis: evidence from three populations. The existence of this journal demonstrates just how interconnected these fields have become in recent decades.
Another influential psychiatry journal that exists on the continuum of Nature journals is Translational Psychiatry, which, by their own words, bridges the gap between the “explosion of knowledge in neuroscience and conceptually novel treatments for our patients that will result in better outcomes than what is provides by existing approaches.” This mission statement is powerful, and to their credit, it’s innovative and continues the recent trend of degrading the boundary that had previously demarcated neuroscience and psychology. In some ways, Molecular Psychiatry is the more granular research usually conducted that eventually gives rise to the type of research published in Translational Psychiatry. Further blending the lines of what defines which field, the journal also reserves the right to publish papers that don’t directly address the core mission of the journal as some research can enhance the translational psychiatry field.
Finally, there’s Nature Reviews Psychology which publishes articles across the entire spectrum of psychological science, its applications, and its wider societal implications.
There is a lot to say about how these fields differ, but this quote, from the book The Perspectives of Psychiatry by Drs. Paul McHugh and Phillip Slavney, summarizes how, at their core, the fields differ philosophically.
In the everyday world of the clinic, psychiatrists are distinguished from other medical specialists not because they are concerned with “minds” rather than “bodies”, but because they focus on complaints appearing in people’s thoughts, perceptions, moods, and behaviours rather than their skins, bones, muscles and viscera … The diagnostic process may be difficult, but causal explanations are always complex and depend on the physician’s capacity to evaluate issues ranging from intermediary metabolism (a “body” issue) to interpersonal misunderstanding (a “mind” issue). Psychiatric concerns thus extend from the ultrastructure of the body to the relationship of groups of minds within a social context.
To practitioners of each of the fields, there is good in discussing how the fields differ. To everybody else, the extent at which time is spent debating how the fields differ matters to the extent that such debates translate to improved research and medicine. The fields of neurology, neuroscience, psychology, and psychiatry are all of incredible importance to each and every one of us and all of us — the scientists, clinicians, patients, their loved ones, and society at large — benefit most greatly when these fields teach, learn, and influence one another to produce good science and clinical research, especially for anybody affected by neurological or psychiatric or multiple disorders.
- About Neuroscience. (n.d.). Department of Neuroscience. Retrieved October 6, 2022, from https://neuro.georgetown.edu/about-neuroscience/
- Abu-Akel, A., Wood, S. J., Upthegrove, R., Chisholm, K., Lin, A., Hansen, P. C., Gillespie, S. M., Apperly, I. A., & Montag, C. (2022). Psychosocial functioning in the balance between autism and psychosis: Evidence from three populations. Molecular Psychiatry, 27(7), Article 7. https://doi.org/10.1038/s41380-022-01543-5
- Adolphs, R. (2002). Recognizing Emotion from Facial Expressions: Psychological and Neurological Mechanisms. Behavioral and Cognitive Neuroscience Reviews, 1(1), 21–62. https://doi.org/10.1177/1534582302001001003
- Are Psychiatric Disorders Brain Diseases? | Psychology Today. (n.d.). Retrieved October 13, 2022, from https://www.psychologytoday.com/us/blog/sacramento-street-psychiatry/201512/are-psychiatric-disorders-brain-diseases
- Considering the Unseen Links to Alzheimer’s: Diet (and how science seems to provide answers) | Neuline. (n.d.-a). Retrieved October 13, 2022, from https://neulinehealth.com/considering-the-unseen-links-to-alzheimers-diet-and-how-science-seems-to-provide-answers/
- Considering the unseen links to Alzheimer’s: Gingivitis | Neuline. (n.d.-b). Retrieved October 13, 2022, from https://neulinehealth.com/considering-the-unseen-links-to-alzheimers-gingivitis/
- David, A. S., & Nicholson, T. (2015). Are neurological and psychiatric disorders different? The British Journal of Psychiatry, 207(5), 373–374. https://doi.org/10.1192/bjp.bp.114.158550
- Fleming, D. K. (2019, July 24). The role of neuroscience in psychology -. Grey Matters | Executive Wellness | Relationship Counseling. https://greymattersintl.com/role-neuroscience-psychology/
- GBD 2017 US Neurological Disorders Collaborators. (2021). Burden of Neurological Disorders Across the US From 1990-2017: A Global Burden of Disease Study. JAMA Neurology, 78(2), 165–176. https://doi.org/10.1001/jamaneurol.2020.4152
- Goesling, J., Lin, L. A., & Clauw, D. J. (2018). Psychiatry and Pain Management: At the Intersection of Chronic Pain and Mental Health. Current Psychiatry Reports, 20(2), 12. https://doi.org/10.1007/s11920-018-0872-4
- Bruce Goldman, Different mental disorders linked to same brain-matter loss, study finds. News Center. Retrieved October 13, 2022, from http://med.stanford.edu/news/all-news/2015/02/different-mental-disorders-cause-same-brain-matter-loss.html
- Health (US), N. I. of, & Study, B. S. C. (2007). Information about Mental Illness and the Brain. In NIH Curriculum Supplement Series [Internet]. National Institutes of Health (US). https://www.ncbi.nlm.nih.gov/books/NBK20369/
- Hellmann-Regen, J., Piber, D., Hinkelmann, K., Gold, S. M., Heesen, C., Spitzer, C., Endres, M., & Otte, C. (2013). Depressive syndromes in neurological disorders. European Archives of Psychiatry and Clinical Neuroscience, 263 Suppl 2, S123-136. https://doi.org/10.1007/s00406-013-0448-6
- Hesdorffer, D. C. (2016). Comorbidity between neurological illness and psychiatric disorders. CNS Spectrums, 21(3), 230–238. https://doi.org/10.1017/S1092852915000929
- Laureys, S., Gosseries, O., & Tononi, G. (2015). The Neurology of Consciousness: Cognitive Neuroscience and Neuropathology. Academic Press.
- Malfliet, A., Coppieters, I., Van Wilgen, P., Kregel, J., De Pauw, R., Dolphens, M., & Ickmans, K. (2017). Brain changes associated with cognitive and emotional factors in chronic pain: A systematic review. European Journal of Pain (London, England), 21(5), 769–786. https://doi.org/10.1002/ejp.1003
- Neurological Disorders | Johns Hopkins Medicine. (n.d.). Retrieved October 9, 2022, from https://www.hopkinsmedicine.org/health/conditions-and-diseases/neurological-disorders
- Nuyen, J., Schellevis, F. G., Satariano, W. A., Spreeuwenberg, P. M., Birkner, M. D., van den Bos, G. A. M., & Groenewegen, P. P. (2006). Comorbidity was associated with neurologic and psychiatric diseases: A general practice-based controlled study. Journal of Clinical Epidemiology, 59(12), 1274–1284. https://doi.org/10.1016/j.jclinepi.2006.01.005
- Paul R. McHugh, M. D. (n.d.). The Perspectives of Psychiatry. Retrieved October 12, 2022, from https://www.press.jhu.edu/books/title/2779/perspectives-psychiatry
- Roca, F., Lang, P.-O., & Chassagne, P. (2019a). Chronic neurological disorders and related comorbidities: Role of age-associated physiological changes. Handbook of Clinical Neurology, 167, 105–122. https://doi.org/10.1016/B978-0-12-804766-8.00007-8
- Roca, F., Lang, P.-O., & Chassagne, P. (2019b). Chapter 7 – Chronic neurological disorders and related comorbidities: Role of age-associated physiological changes. In S. T. Dekosky & S. Asthana (Eds.), Handbook of Clinical Neurology (Vol. 167, pp. 105–122). Elsevier. https://doi.org/10.1016/B978-0-12-804766-8.00007-8
- Smythies, J. (1996). A Note on the Concept of the Visual Field in Neurology, Psychology, and Visual Neuroscience. Perception, 25(3), 369–371. https://doi.org/10.1068/p250369
- The Biology of Depression | Psychology Today. (n.d.). Retrieved October 17, 2022, from https://www.psychologytoday.com/us/basics/depression/the-biology-depression
- The Brain and Common Psychiatric Disorders | Psychology Today. (n.d.). Retrieved October 13, 2022, from https://www.psychologytoday.com/us/basics/neuroscience/the-brain-and-common-psychiatric-disorders
- The emergence of modern neuroscience: Some implications for neurology and psychiatry – ProQuest. (n.d.). Retrieved October 6, 2022, from https://www.proquest.com/openview/23494252f3585ec9d605e82d7b3af6e2/1?pq-origsite=gscholar&cbl=48084
- Valderas, J. M., Starfield, B., Sibbald, B., Salisbury, C., & Roland, M. (2009). Defining Comorbidity: Implications for Understanding Health and Health Services. Annals of Family Medicine, 7(4), 357–363. https://doi.org/10.1370/afm.983
- What Does Having a “Mental Health Disorder” Actually Mean? | Psychology Today. (n.d.). Retrieved October 13, 2022, from https://www.psychologytoday.com/us/blog/7-billion-brains/202001/what-does-having-mental-health-disorder-actually-mean
- Yang, Y., Wang, C., Xiang, Y., Lu, J., & Penzel, T. (2020). Editorial: Mental Disorders Associated With Neurological Diseases. Frontiers in Psychiatry, 11. https://www.frontiersin.org/articles/10.3389/fpsyt.2020.00196
- Zhang, F., Peng, W., Sweeney, J. A., Jia, Z., & Gong, Q. (2018). Brain structure alterations in depression: Psychoradiological evidence. CNS Neuroscience & Therapeutics, 24(11), 994–1003. https://doi.org/10.1111/cns.12835