The “spectrumization” of neurological disorders
Historically and socially, psychiatric diseases have been defined as these yes-or-no disorders of the brain: he has schizophrenia, he doesn’t. He has autism, he doesn’t. For the cases that were not crystal clear, the neurologist just had to take his or her best guess as to whether or not the patient suffered from a disease, or whether the patient was within the boundaries of normal. But with the ever-increasing understanding of how absurdly complex the brain is came a shift toward a “spectrumization” of psychiatric disorders. Researchers and physicians started noticing just how similar some of these psychiatric patients were in their biomarkers, even though they had different diagnoses. Patients were no longer simply a binary diagnosis, but became a single point along a spectrum of symptoms and disorders.
With this newer view on psychiatric disorders, there is currently much more flexibility in terms of the diagnosis of an individual. The most well-known of these spectrum disorders is the autism spectrum disorders (ASD) that include Asperger’s to full blown autism to Rett’s syndrome. Side note: all of these are thought to be developmental disorders, along with schizophrenia, demonstrating just how ridiculously important the proper development of the nervous system is. I’ll write more on this later since neurodevelopment is just so ridiculously interesting. Each of these autism spectrum disorders has some or many overlapping symptoms with one another (behavioral, electrophysiological, genetic etc.), with varying degrees of severity. However, each disorder still has its own unique symptom or combination of symptom(s) that make it its own disorder. This is true for mood disorders (depression, bipolar, etc.) and other psychiatric disorders too (different symptoms of schizoprenia and schizoid disorders for example). I am sure that our classification scheme for psychiatric disorders will change as the research into these fields becomes even more fruitful.
It isn’t wholly surprising that this trend has developed. We know the brain to be a very densely packed mess of highly connected cells that communicate with each other using a myriad of different chemical compounds. The effect of subtle but significant changes in the wiring and firing patterns of these neurons can be quite large, and similar changes between individuals at the level of neuronal connections can lead to similar changes at a higher level such as behavior. What complicates matters is that in many instances the same abnormalities at the circuitry level can be caused by different molecular and genetic underpinnings, and that very similar circuit level differences can in fact lead to vastly different behavioral outputs. Most psychiatric illness diagnoses are at the level of behavior currently, but there is a huge push in neuroscience research to find reliable biomarkers that are not as subjective as behavioral tests.
This of course stems from the belief that all thoughts, feelings, emotions, and consciousness are firmly rooted in the physical world ie our neurons within our brain. If you are a believer in dualism (a la Descartes) then this obviously does not apply, but I find it very difficult to believe in dualism with our current understanding of our nervous system, as limited as it may be. If the thoughts of an individual are irrational, delusional and/or fly in the face of reason and evidence, then it follows that something must be different in the substrate responsible for these thoughts when compared with a “normal” substrate. But, how does one define a brain as being normal? This is a tough question that I don’t have a good answer for, as it is a mix of both biological and social criteria that defines a “normal” brain. But, I imagine that there is quite a broad spectrum of what can be categorized as “normal”, just as there are broad spectrums for the various diseases as well.
