It's perhaps the most stigmatized and misunderstood psychological disorder of them all, even among psychologists. Maybe because it's pretty rare, affecting about 1% of the population, schizophrenia causes more anxiety in the media, in the public, and even in doctors' offices than any other mental illness.   As a result, its sufferers have often been shunned, abused, or locked up. And among the many fallacies that surround the disorder is simply what it means. The word "schizophrenia" literally means "split mind" but contrary to popular belief, the condition has nothing to do with a split in personality or multiple personalities.   The term refers instead to what's sometimes called a "split from reality."  Multiple Personality Disorder, now known as Dissociative Identity Disorder, is a totally different type of condition, a kind of dissociative disorder. And these two are shrouded in misconceptions, partly because they were the subject of, probably, the greatest psychological hoax of all time.   While many of us can relate on some level to the emotional swings, nervousness, and compulsions that come with mood and anxiety disorders, it can be a lot harder for those without direct experience to relate to the symptoms of schizophrenia and dissociation.   Unfortunately we tend to fear and avoid what we don't understand in each other, whether it's a friend of family member or just some stranger on the bus. But thankfully part of the psychologist's job is to demystify the things that can happen in our heads, and is often the case, understanding may be the key to compassion.   Schizophrenia is a chronic condition that usually surfaces for men in their early to mid-20s, and for women in their late 20s. For some the disorder comes on gradually, but for others it could arise more suddenly, perhaps triggered by stress or trauma, although no event can actually cause the disorder.   Once  thought of as a single discrete condition, schizophrenia is now included in the DSM-5 as a point on a spectrum of disorders that vary in how they're expressed and how long they last, but they share similar symptoms.   Schizophrenia Spectrum Disorders are currently thought of as characterized by disorganized thinking; emotions and behaviors that are often incongruent with their situations; and disturbed perceptions, including delusions and hallucinations.   They all involve a kind of loss of contact with reality on some level. The resulting behaviors and mental states associated with this break from reality are generally called "psychotic symptoms" and they usually impair the ability to function.   When someone's experiencing psychotic symptoms, their thinking and speech can become disorganized, rambling and fragmented. This tendency to pick up one train of thought and suddenly switch to another and then another can make communication painfully difficult.   People exhibiting these symptoms can also suffer a breakdown in selective attention, losing the ability to focus on one thing while filtering others out.   In extreme cases, speech may become so fragmented it becomes little more than a string of meaningless words, a condition given a name that sounds like its own kind of non sequitur, "word salad."   Classic schizophrenia is also often marked by delusions or false beliefs not based in reality. These delusions can be rooted in ideas of grandeur like "I'm the queen of England!" or "I won an Olympic gold medal for the luge!"  Or they can become narratives of persecution and paranoia, believing your thoughts and actions are being controlled by an outside force or that you're being spied on or followed or that you're on the verge of a major catastrophe.   And there are some complicated variations on these delusions, like feeling that you've died or don't exist anymore or that someone's madly in love with you or that you're infested with parasites.   Delusions of one kind of another strike as many as four out of five people with schizophrenia.  While some delusions can seem fairly logical, they can also be severe and bizarre and frightening.   Unfortunately maybe the most memorable examples of people suffering from severe delusions come from serial killers and yeah, while Son of Sam did claim that he was taking orders from his neighbor's dog, that kind of stuff is in the tiny, tiny, tiny minority.   Brian Wilson of The Beach Boys and Syd Barrett of Pink Floyd both suffered psychotic symptoms.  And then of course there's John Nash, the Nobel Prize winning American mathematician and subject of "A Beautiful Mind."   Through proper treatment, some people with schizophrenia have not only learned to live with their illness but also made fantastic creative contributions to the world.   Maybe people with schizophrenia also suffer from perceptual disturbances, or sensory experiences that come without any apparent sensory stimulation, like hallucinations.  This is when a person sees or hears something that isn't there, often lacking the ability to understand what is real and what isn't.   Auditory hallucinations, or hearing voices, are the most common form, and these voices are often abusive.  It's as if you're inner monologue, that conversation that you have with yourself or the random things that float through your head, are somehow coming from outside of you.  It's as if you couldn't sort out whether the voices in your mind were internal and self-generated, or external and other-generated.   To me, it sounds terrifying.   Other common symptoms include disorganized, abnormal, or incongruent behavior and emotions.  This could mean laughing when recalling a loved one's death or crying while others are laughing. Acting like a goofy child one minute then becoming unpredictably angry or agitated the next.   Movements may become inappropriate and compulsive, like continually rocking back and forth or remaining motionless for hours.   Broadly, most psychotic symptoms fall into three general categories traditionally used by psychologists: positive, negative, and disorganized symptoms.   Positive symptoms are not what they sound like.  They're the type that adds something to the experience of the patient. Like, for example, hallucinations or inappropriate laughter or tears or delusional thoughts.   Negative symptoms refer to those that subtract from normal behavior, like a reduced ability to function, neglect of personal hygiene, lack of emotion, toneless voice, expressionless face, or withdrawal from family and friends.   Finally, disorganized symptoms are those jumbles of thought or speech that could include word salad and other problems with attention and organization.   Symptoms like these are useful in diagnosing a disorder on the schizophrenia spectrum, but there's a physiological component too. Like many of the disorders we've talked about, schizophrenia has been associated with a number of brain abnormalities.   Post mortem research on schizophrenia patients has found that many have extra receptors for dopamine, a neurotransmitter involved in emotion regulation and the brain's pleasure and reward centers.   Some researchers think that overly responsive dopamine systems might magnify brain activity in some way, perhaps creating hallucinations and other so-called positive symptoms as the brain loses its capacity to tell the difference between internal and external stimuli.   For this reason, dopamine blocking drugs are often used as anti-psychotic medications in treatment.  Modern neuroimaging studies also show that some people with schizophrenia have abnormal brain activity in several different parts of the brain.   One study noted that when patients were hallucinating, for example, there was unusually high activity in the thalamus, which is involved in filtering incoming sensory signals.  Another study noted that patients with paranoid symptoms showed over-activity in the fear processing amygdala.   So, schizophrenia seems to involve not just problems with one part of the brain, but abnormalities in several areas and their interconnections.   But what might be causing these abnormalities?   Earlier I mentioned how a stressful event might trigger psychotic symptoms for the first time, even though it can't actually create the disorder. Psychologists call this the "diathesis-stress model."   This way of thinking involves a combination of biological and genetic vulnerabilities -- diathesis -- and environmental stressors -- stress -- that both contribute to the onset of schizophrenia. This model helps explain why some people with genetic vulnerability might not always develop schizophrenia and why the rates of schizophrenia tend to be higher with some degree of poverty or socioeconomic stress.   And it seems too that there is some kind of genetic predisposition for the disorder.  The one-in-a-hundred odds of developing schizophrenia jumped to nearly one in ten if you have a parent or sibling with the disorder, with about 50/50 odds if that sibling is an identical twin, even if those twins were raised apart.   One recent landmark seven year study looked at genetic samples across 35 countries, examining more than 35,000 people with schizophrenia, and another 110,000 without the disorder.   The study identified more than 100 genes that may increase the risk of schizophrenia.  As expected, some of these genes involve dopamine regulation, but others are related to immune system functioning.  Researchers continue to tease out what is exactly going on here, but many are hopeful that these new findings will lead to better treatment.   Clearly, schizophrenia is a challenging disorder to live with and one that's hard for outsiders to understand, but maybe even more rare and more elusive are the dissociative disorders.   These are disorders of consciousness, called dissociative because they're marked by an interruption in conscious awareness.  Patients can become separated from the thoughts or feelings that they use to have, which can result in a sudden loss of memory or even change in identity.   Now, we might all experience minor dissociation at times, like maybe the sense that you're watching yourself from above, as in a movie, or like you're driving home and get so zoned out that suddenly you find yourself in front of Taco Bell thinking, like, "How did I get here?"   Those things would generally fall into the normal range of dissociation, but most of us don't develop different personalities.   Dissociative disorders come in several different forms, but the most infamous of the bunch is probably Dissociative Identity Disorder. This has long been known as Multiple Personality Disorder and, yes, it is a thing.  It's a rare and flashy disorder in which a person exhibits two or more distinct and alternating identities and the best known case was that of Shirley Mason, whose story was famously rendered in the 1973 best seller "Sybil" and later in a popular mini-series.   The book was marketed as the true story of a woman who suffered great childhood trauma and ended up with 16 different personalities, ranging from Vicky, a selfish French Woman, to handyman Syd, to the religious and critical Clara.   The book became a craze and within a few years reported cases of multiple personality skyrocketed from scarcely 100 to nearly 40,000.   Many people think the book was essentially responsible for creating a new psychiatric diagnosis.  It turns out though, Sybil's story was a big fat lie.   Yes, Shirley Mason was a real person and one with a troubled, traumatic past and a number of psychological issues.  As a student in New York in the 1950s she started seeing a therapist named Connie Wilbur and taking some heavy medications.  And somewhere in there, maybe because she was coaxed, or maybe because she wanted more attention, Shirley started expressing different personalities.   Dr. Wilbur built a career and a book deal out of her star patient, even after Shirley confessed that her split personality was a ruse.   This simple case is a powerful reminder that we really don't understand dissociative disorders very well or even know if they're always real. Indeed, some people question if Dissociative Identity Disorder is an actual disorder at all.   But some studies have shown distinct body and brain states that seem to appear in different identities, things like one personality being right handed while the other is left handed, or different personalities having variations in their eye sight that ophthalmologists could actually detect.   In these cases, dissociations of identity may be in response to stress or anxiety, a sort of extreme coping mechanism.   Either way, the debate and the research continue.   Today we talked about the major symptoms associated with schizophrenia spectrum disorders, including disorganized thinking, inappropriate emotions and behaviors, and disturbed perceptions.   We also discussed brain activity associated with these disorders and talked about their possible origins including the diathesis stress model.   You also learned about dissociative disorders, and Dissociative Identity Disorder in particular, and the scandal that was the Sybil case.   Thanks for watching, especially to all of our Subbable subscribers who make Crash Course possible. To find out how you can become a supporter, just go to subbable.com.   This episode was written by Kathleen Yale, edited by Blake de Pastino, and our consultant is Dr. Ranjit Bhagwat. Our director and editor is Nicholas Jenkins, the script supervisor is Michael Aranda. He is also our sound designer and the graphics team at Thought Cafe.