Diagnosing mental illness is all the more difficult because the constellation of symptoms not only varies from person to person but also often fluctuates over time within an individual. Not everyone afflicted with schizophrenia screams in distress, for instance; some people with the disease may shut down and stop communicating. Likewise, people with dementia may be attentive and engaged one minute and detached and withdrawn the next. Even more challenging, some indications of mental illness may be exaggerations of normal personality traits, making the behaviors particularly hard to recognize as pathological. With people who are naturally frank and outspoken, the lack of judgment that can accompany dementia may at first be construed as their typical bluntness. Similarly, when introverted people become more withdrawn, others may not realize that they are exhibiting symptoms of Alzheimer’s disease.
For researchers, it’s becoming clearer that specific mental disorders are not well-defined categories of illness, each delineated by a distinct set of symptoms and biological indicators. The same symptoms may not even be caused by the same illness, so two people who exhibit the same erratic behavior may in fact be suffering from two completely different disorders. Or perhaps there is overlap among various mental disorders in terms of symptoms, biological mechanisms, and causes. Some genetic and clinical analyses find similarities across a wide variety of diagnoses, suggesting that mental illnesses share a common neurobiological substrate. Modern science is currently exploring this possibility.
Today, scientists are quite confident that the main site of disruption in people with mental illness is the highly evolved prefrontal cortex, which sits at the front of the brain, and its network of connections with other parts of the brain. But what these abnormalities are and how exactly the brain malfunctions in various mental problems remains a puzzle.
When a person’s behavioral changes are triggered by brain tumors, as mine were, it may seem easy to establish a cause-and-effect relationship between neurological factors and behaviors. Neurologists like to try to localize every problem to a particular part of the brain, and sometimes that’s more or less possible. But metastatic brain tumors—whether from melanoma or breast cancer or lung cancer—tend to involve multiple parts of the brain at the same time. When you have two or more tumors, as I did, it becomes especially difficult to figure out what part of the brain is affecting what behaviors. In addition, when there is extensive swelling from tumors and treatments, the entire brain contributes to the altered behavior.
While we don’t know exactly what took place in my brain or where precisely it happened, my journey has given me an invaluable opportunity to tour the landscape of the brain. As a result, I’ve come to better understand this breathtakingly complex structure and its incredibly resilient product: the human mind.
As with everyone who suffers from mental disorders, I experienced a constellation of symptoms during my brush with madness that were unique to my case. But during my brief mental breakdown, I exhibited many symptoms described in the Diagnostic and Statistical Manual of Mental Disorders, fifth edition (DSM-5), the official guide clinicians and researchers use to classify various mental illnesses. For that reason, the similarity between my experience and that of people with a wide range of mental illnesses—from Alzheimer’s to other dementias, from bipolar disorder to schizophrenia—is remarkable. Identifying these parallels and using them to better understand the experience and causes of mental illness is one of my main goals in this book.
I gained a deep understanding of what it is like to live in a world that makes no sense, that’s bewildering and unfamiliar. I know what it’s like to be so confused that you trust no one, least of all those closest to you, who you may be convinced are conspiring against you. I know how it feels to lose not only the powers of insight, judgment, and spatial recognition but also the faculties essential for communication, such as the ability to read. Perhaps most chilling, I also know what it’s like to be completely unaware of these deficits. It was only after my mind began to return that I learned how warped my reality had been.
After I emerged from that dark space and was given a second chance at sanity, I wanted to explore, as a neuroscientist, what went wrong in my brain. I learned that my frontal and parietal lobes—which are responsible for many of our most human behaviors—were malfunctioning. This helps to explain why I behaved in ways similar to people with mental illness: why I got lost in familiar places, forgot things that had just happened to me, and became angry, mean, and unloving to my family; why I became obsessed with strange little details like what I was having for breakfast while ignoring the fact I was about to die; and, most striking, why I failed to notice any of these insidious changes in myself. Even as my mind was deteriorating, I couldn’t see that I was slipping into mental illness.
In addition to providing insight into mental illnesses such as schizophrenia and dementia, my experience gave me a greater understanding of other brain disabilities, including the mental declines that many of us encounter as we age. Many people may someday face in themselves, their partners, or their parents the bewildering mental changes I had—memory loss, disinhibited and inappropriate behaviors, altered personality, and the inability to recognize these problems in oneself. The frontal cortex, the part of my brain that was most affected by my tumors and treatment-induced swelling, is one of the regions that often begin to fail
