One thing that’s always frustrated me about behavioral science (and I’m sure this has frustrated other people) is the lack of a set of clear explanations of the cause of mental illnesses. Many different mechanisms have been proposed historically: Benjamin Rush, one of the forefathers of American medicine, proposed that madness was the result of poor blood flow to the brain; Sigmund Freud suggested it was due to failures to resolve sexual tension in socially appropriate ways; modern medicine places considerable emphasis on the role of changes in neurotransmitter production and activity.
In all likelihood, individual cases may be due to any number of factors given the high prevalence and considerable diversity of symptoms seen among patients treated for psychiatric disorders. However, another curious association is beginning to emerge which links mental health issues to bacterial infections.
A large-scale study from Denmark found that a history of streptococcal throat infections was associated with an increased risk of developing a mental disorder, especially obsessive compulsive disorder or tic disorders such as Tourette’s. In good scientific style, the authors were quick to clarify that these results do not indicate that infections cause mental illness, as there may be an underlying factors (e.g. genetics, environment, etc.) which leaves individuals vulnerable to both infections and mental disorders.
However, there is still reason to believe that infectious diseases may contribute directly to deleterious changes in brain function. Studies have shown that herpes virus can be found in the brains of patients with Alzheimer’s disease. Herpes infection at the skin of the face can creep back along axons of the trigeminal nerve, leading to infection of the brain -- which can sometimes cause a deadly condition known as herpesviral encephalitis. Though this particular mechanism isn’t a likely cause of cases of mental illnesses, it hardly shuts the door on this subject.
It is interesting to examine the comorbidities of certain diseases and mental illness as there remains so much unknown, and there are so many. In an article observing Tourette's syndrome researchers found that in addition to tics, children with Tourette's can show a variety of comorbid psychopathologies, including learning difficulties, sleep abnormalities, anxiety, obsessive-compulsive disorder (OCD), and attention deficit hyperactivity disorder (ADHD) (Caligiore, 2017). As tics progress, often mental illness will progress along with the disease. This could be due to the patient not feeling socially accepted which can lead to isolation and depression only worsening the symptoms. Depression and anxiety play major roles in the risk of developing a mental health disorder. Future studies should address these correlations more thoroughly.
ReplyDeleteCaligiore, Daniele, et al. Dysfunctions of the Basal Ganglia-Cerebellar-Thalamo-Cortical System Produce Motor Tics in Tourette Syndrome. Plos One, Public Library of Science, 30 Mar. 2017.