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The Origins of Mental Illness

(with special thanks to Dr. Jens Foell for edits and suggestions)

(image of positron emission tomography [PET] scans borrowed from the Mayo Clinic)

As a person with borderline personality disorder, I have often received the question, “When did you develop BPD?” As it turns out, the answer is not as straightforward as it may seem.

First of all, we – meaning neuroscientists and mental health professionals – don’t yet know how to test for mental health issues the way we can test for physical maladies like, say, cancer. It’s not a simple matter of looking at a person’s brain and seeing the evidence of BPD. That’s because BPD is a psychiatric illness, not a neurological one.

I know that’s a confusing distinction, so let me draw an analogy to make it more clear. The difference between these two types of medical problems is very similar to the difference between the “brain” and the “mind” (literally: “neuro” means “brain” and “psych” means “mind”). Neurological problems affect the literal structure of the brain. This includes brain tumors, strokes, head injuries, brain aneurysms, or any other sort of physical lesion in the brain (“lesion” translates to “damage”). Psychiatric (otherwise known as “mental” or “psychological”) illnesses, by contrast, are associated with the brain’s faulty chemical flow. If you have a psychiatric problem, it stems from the irregular exchange of chemicals in your brain. As you can imagine, tracking the movement of incredibly small molecules is often much more difficult than tracking physical brain damage, which makes psychiatric issues much harder to spot with medical tests than neurological issues are. A further level of complication arises with mental illnesses because their physical makeup in the brain is affected by the emotions that the brain experiences. As opposed to most neurological issues, the chemical composition of a psychological illness is altered by the host’s environment, as well as the emotions that affect them. Much like a quantum physics problem, which changes when it’s observed, psychiatric disease responds to everyday events whether they’re intended to change the illness or not, which makes it even more difficult to trace that illness to its origin.

Another complicating factor in tracking the origins of mental illness is the difficulty that even trained mental health professionals have in identifying the difference between “normal” and “abnormal” moods. To use a common example, childhood presents an emotionally rough time in a person’s life. Children have the tendency to blow up over small adversities that would roll off their parents’ backs. Their brains are still forming, which accounts in part for their volatile and intense moods. Fighting through the fog of this constant neural transition we call pubescence, how is anyone to know whether a child’s thoughts, feelings, behaviors, and subjective experiences fall on a healthy spectrum or extend into the realm of mental illness?

If an adult speaks to imaginary friends, they’re screened for schizophrenia. If a child speaks to imaginary friends, they’re praised for being “creative” and are encouraged to play in their fantasy land. At what age does a silly childhood game become a psychotic disease? If the child grows up to become schizophrenic, were their kindergarten imaginary friends innocent, or were they always the result of psychosis?

These are the kinds of questions researchers and clinicians have been trying to answer for as long as the field of psychiatry has been alive. Much to the medical community’s continued frustration, there doesn’t seem to be a consistent answer to any of them. There is no magical age at which creativity becomes madness. Those who are diagnosed with a mental health problem at any age can’t always easily figure out when their symptoms began to manifest. Often, hindsight is a psychiatrist’s only diagnostic tool.

Even if it were easier to pinpoint the moments at which specific mental health issues begin to affect a person outwardly, that doesn’t necessarily have anything to do with when the disease originated internally. That’s because psychiatric symptoms often lie dormant until they are triggered into activity. Triggering circumstances range far and wide, but most of them have to do with stressful events in a person’s life, whether it’s emotional or physical abuse, falling behind in school, or simply undergoing the physical and psychological changes associated with the preteen years.

So if a psychiatric disease can lie dormant in a person’s brain until it’s triggered, how do we know when that person developed the predisposition to become symptomatic? In other words, if they’re sick on the inside before they feel sick on the outside, when did they actually become sick on the inside? The answer, of course, is complicated and context-dependent. It’s becoming increasingly clear that many mental health issues take root in a person’s genealogy, which develops in the womb. In that case, the disease is genetic. This is usually easy to determine if symptoms develop at an extremely young age, and/or the mentally ill person’s parents share the same symptoms.

However, not every psychiatric disease is passed down genetically. Often, a baby is born mentally healthy, but due to environmental circumstances, they develop psychiatric problems later in life. To be clear, they don’t contract these illnesses; the word “contract” implies the disease is transmitted physically from an outside source. With the rare exception of certain diseases like neurosyphilis, which can cause various psychiatric symptoms and which may develop when syphilis is contracted sexually, mental disorders usually develop without the direct influence of a physical instigator. Instead, they may develop in response to environmental triggers. For example, post-traumatic stress disorder (PTSD) may develop in a person’s brain in response to an extremely stressful or threatening surrounding environment. However, no physical part of that environment literally enters the person’s brain and causes PTSD to develop. Instead, the mental illness grows in response to the intangible perception of danger. (Side note: People are often genetically predisposed to develop problems like PTSD or not, which is a large reason why the same stressful scenario may cause symptoms to develop in one person but not another. In that sense, some psychiatric illnesses may be both acquirable and inheritable.)

Many environmentally-triggered mental diseases develop this way: as a response to stress (especially if it’s chronic). However, because the link between the source of stress and the unhealthy mental response to that stress is intangible, it’s extremely difficult to determine which symptoms are caused by which environmental factors. This challenging task makes up a large percentage of any practicing psychiatrist’s responsibility: linking their patients’ mental symptoms to their respective causes based on the patients’ (possibly inaccurate or biased) descriptions of their past experiences.

More than with any other medical practice, in psychiatry, the doctor has to rely on the ill person’s ability to explain what they’re going through in order to make a diagnosis. Typically, the most tangible physical evidence  of mental disease that a psychiatrist can possibly perceive is their patients’ behavior or countenance. Measuring either of those things is a subjective challenge that cannot be defined with a physical marker. This makes tracing the origins of mental illness an exceedingly murky goal, and one which medical science is diligently taking steps to illuminate as soon as possible.

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