Chapter 6

Mental States and Mental Disorders

As I discussed in Part One, one of the dilemmas in the mental health field is distinguishing between normal human emotions and mental disorders, especially since the symptoms can be the same. We all get anxious or mildly depressed from time to time. If we experience a devastating loss, such as the unexpected death of a spouse, we may get severely depressed for a period. These are all normal reactions. They are hardwired into our brains.

However, when people are exposed to numerous stressors all at once, or when the stressors are extreme or overwhelming (such as being violently assaulted), these normal and understandable initial reactions can quickly lead to what we call “mental illness.” The diagnoses are all over the map. Trauma or extreme stress can lead to anxiety disorders, depression, PTSD, eating disorders, substance use disorders, personality disorders, and even psychosis. How do stress and trauma lead to all these different disorders? And where is the line between a normal reaction to adversity and a disorder?

Two issues have made these questions particularly difficult to answer: (1) the symptoms are the same, and (2) both mental states and mental disorders can lead to poor health outcomes. Nonetheless, distinguishing between normal mental states and mental disorders is critically important. Mental states are adaptive reactions to adversity. Mental disorders represent the brain malfunctioning. These distinctions have direct implications for treatment. Helping people cope with adversity is very different than treating a brain that is malfunctioning.

Understanding “Normal”: Stress and the Stress Response

Stressors are the psychological and social factors in the biopsychosocial model—the ones that people usually think of as the “mental” causes of mental illness.

Many clinicians and researchers still see biological factors as separate from psychological and social ones. For example, they might believe that hallucinations are due to a biological chemical imbalance, but that someone with schizophrenia can also suffer from low self-esteem, which is a psychological problem. They may try to address both, but they often see these issues as unrelated and separate. One requires medication, and the other requires talk therapy. I disagree with this dichotomous view. I think biological, psychological, and social factors are all interconnected and inseparable. Biology influences our psychology and how we get along with others. But our psychology and our interactions with other people influence our biology. These connections can impact all mental and metabolic symptoms. To begin unpacking this, let me start by making some overarching observations about our species.

Humans are meant to live in groups. We seek out and attach to other people—parents, lovers, children, friends, teachers, and community members. These connections form a network of safety and support in our lives. We are biologically driven to want, and even need, these people. There is a conundrum, though: While we must live with other people, other people are actually the primary sources of psychological and social stress. Most of these stressors revolve around relationships, roles, resources, and responsibilities. People can be stressed over expectations on them, financial problems, performance problems, relationship problems, or status in society. Some people experience chronic stressors due to socioeconomic status, abuse, neglect, race, ethnicity, religious beliefs, physical abilities, cognitive abilities, gender identity, sexual orientation, age, and so many other factors. People can be harmed or threatened by other people. We sometimes make each other feel unsafe. We sometimes make other humans feel like they aren’t good enough. There are countless reasons that humans stress other humans. And interestingly, the absence of other humans, or loneliness, is also a powerful stressor unto itself.

All of these stressors lead to the stress response, a complex array of biological changes in the brain and body. The stress response includes changes in four domains:

All of these changes, in turn, affect metabolism. They comprise a person’s response to adversity. They are not disorders. They set the stage for “fight or flight.” However, in most day-to-day stressful situations, we don’t fight or flee. Instead, we just stay put—but we get angry, or anxious, or irritable, or overwhelmed, or confused, or terrified, or hurt, or sad. Yet these core changes are still occurring in our bodies and brains.

Different stressful situations result in different behaviors and emotions. Some stressors make you want to yell at someone, such as the driver who cuts you off in traffic and then flips you off for no reason. Other stressors might make you ruminate and not sleep well, such as feeling unprepared for an important exam the next day. Others might make you want to curl up into a ball and cry, such as getting dumped by the love of your life. All of these situations involve the stress response. While similar mechanisms are involved, clear differences trigger different brain regions to create different responses.

Although these are normal, the stress response takes a toll—a metabolic toll. The body uses energy to produce these changes, meaning less energy is available for other functions. Many of these responses create a state of high alert. In some situations, the person feels threatened and prepares to fight or argue with someone. In other situations, the person may feel wounded, vulnerable, or powerless and try to hide from the world. In either case, metabolic resources are being mobilized. The heart is pumping faster. Blood pressure is increasing. Blood glucose is rising. Hormones are flowing. Inflammatory cytokines are being released. The body is mounting resources and energy for its own defense.

When the stress is mild, people who are resilient and metabolically healthy deal with it. It can be over in a matter of seconds or minutes.

However, if a body is metabolically compromised, or if the stress is extreme, people can be pushed over the edge, and a new mental or metabolic disorder can quickly emerge. For those with preexisting disorders, symptoms can become even worse. That’s right: Stress can exacerbate every known mental and metabolic disorder. People with depression may get more depressed. People with alcoholism may fall off the wagon. People with schizophrenia may hallucinate. People with Alzheimer’s disease may get agitated and combative. People with epilepsy may experience a seizure. People with diabetes may have their blood sugar skyrocket. And people with cardiovascular disease may have chest pain or a heart attack. Some people die—from stress alone. This is all well established.

A separate medical field has tried to make sense of all of this—the field of psychosomatic medicine or mind-body medicine. Many healthcare professionals have observed the relationship between psychological and social factors affecting the health of the body. Practitioners in this field understand that all these risk factors play a role in human physiology. These factors are often referred to as the social determinants of health. Many social factors, such as poverty, abuse, or living in a high-crime neighborhood, can have huge consequences on health and longevity.

Some of the most compelling data on this comes from the adverse childhood experiences (ACEs) studies that started between 1995 and 1997 and looked at the number of adverse experiences that children and adolescents encounter and their effects on long-term health outcomes, both physical and mental. These ongoing studies have looked at stressors early in life, such as physical and sexual abuse, neglect, household substance abuse, household mental illness, exposure to domestic violence, and parental divorce, and then determined if these early experiences were associated with later health outcomes. A 2017 meta-analysis of thirty-seven such studies looking at twenty-three health outcomes in more than 250,000 people found that they are.² The more ACEs a child has, the more likely he or she will have poor health outcomes. ACEs increase the probability for physical inactivity, obesity, and diabetes by 25 to 52 percent. They are associated with two to three times higher rates of smoking, poor self-rated health, cancer, heart disease, and respiratory disease. ACEs lead to a three- to sixfold increase in the rates of sexual risk-taking, poor mental health, problematic alcohol use, and illicit drug use. They also lead to more than a sevenfold increase in being the victim or perpetrator of violence, a tenfold increase in problematic drug use, and a thirtyfold increase in suicide attempts. ACEs clearly affect mortality. One study of 17,000 people that looked specifically at mortality data estimated that having six or more ACEs takes twenty years off a person’s life compared to those with no ACEs.³

These studies have led many people to conclude that ACEs cause both physical and mental illnesses. Some experts have gone so far as to suggest that ACEs, in particular childhood trauma and abuse, are likely the common pathway to all mental disorders. But let me remind you, these are correlations. They don’t prove causation. More importantly, not everyone who has a horrible childhood develops a mental disorder, and many people who end up with mental disorders have perfectly fine childhoods. Nonetheless, if these adverse experiences are playing some role in these different disorders, how does that work? What is happening in the body and brain to cause all of this?

Limited Resources

For decades, researchers have been studying the biological effects of stress on the brain and body to better understand these relationships, hoping to identify the cause-and-effect pathways from stressful life events to poor health outcomes.

We know that when the body is stressed, metabolic resources are being diverted to the fight-or-flight system. This leaves less energy available for other functions. Any cells that were already struggling can begin to fail. This can lead to metabolic and mental symptoms.

Stress also impairs the body’s ability to maintain itself. Cells engage in housekeeping functions daily. They get rid of damaged cell parts, various waste molecules, and misfolded proteins, and they make new ones to take their places in a process often called autophagy. Auto means “self” and phagy means “eat,” so this term literally means “to eat yourself.” Our cells degrade these old parts in waste-disposal systems called lysosomes. Some of this material is recycled and used to make new parts. High levels of cortisol have been found to inhibit autophagy, slowing down or stopping this maintenance process.⁴ Problems with autophagy have been found in a wide variety of disorders including neurodegenerative, neurodevelopmental, autoimmune, inflammatory, cancer, schizophrenia, bipolar disorder, autism, alcoholism, and major depression.⁵ Disturbances in autophagy are known to affect neuroplasticity and the maintenance of brain cells.⁶

In addition to problems with autophagy, when cells are stressed, they also slow the process of making new proteins. This appears to conserve metabolic resources for the body’s defense system. One way they delay making these proteins is by sequestering messenger RNA molecules (the instructions for new proteins) into little bubbles called “stress granules.”⁷ These have been associated with neurodegenerative disorders, and high levels of cortisol stimulate their production.⁸

One additional way that stress can lead to maintenance problems is through sleep disruption. It is well established that stress can lead to insomnia. Sleep is critically important to both physical and mental health. It’s a time when the body prioritizes maintenance functions. When people aren’t sleeping well, their bodies aren’t doing this maintenance work. On top of that, sleep deprivation, in and of itself, is stressful and can lead to higher levels of cortisol, which can make the problem even worse.

All this stress, regardless of when it occurs, results in premature aging. I’ve already mentioned that all mental disorders are associated with premature aging, but stress alone can also cause it. One study tried to quantify the effects of stress on aging.⁹ The study recruited fifty-eight healthy premenopausal women who were mothers to either healthy or chronically ill children. The women’s average age was thirty-eight, and they did not yet have identified health problems. The researchers assessed three metrics of aging and asked the mothers to rate their perceived levels of stress. The mothers with the highest levels of stress over the longest periods of time showed signs of accelerated aging compared to the lowest-stress women. On average, they aged ten years faster.

Stress clearly plays a role in human health and takes a serious metabolic toll. It uses energy that could otherwise be used for proper cell function and maintenance. When people are stressed in extreme ways or for prolonged periods of time, their bodies can get worn down and begin to malfunction, resulting in various physical and mental disorders, or just plain old aging. If the brain or body are already compromised and vulnerable, stress can make symptoms worse, because the energy needed for the stress response is diverting energy from these vulnerable cells.

Stress-reduction practices, such as mindfulness, meditation, or yoga, can play a powerful role in treatment (more on that in Part Three). However, they aren’t the solution for everyone. If a person is living in an adverse environment, turning off the stress response may not be possible or even advisable. Soldiers fighting in a war are in danger. And while their service directly results in greater risks for mental and metabolic disorders, their heightened stress response is protecting them. The same applies to people in dangerous neighborhoods. Instructing people in dangerous environments to take deep breaths and be mindful isn’t the full answer. When they get to safety, these strategies might play a role, but the damage may already be done by then.

Furthermore, stress may not be the cause of one’s mental illness at all. In that case, stress-reduction techniques likely won’t be all that helpful.

Understanding “Disorders”: A New Definition of Mental Illness

As I discussed in earlier chapters, the current classification of mental disorders is fraught with problems—heterogeneity, comorbidity, and a lack of validity. None of the diagnoses are true and distinct disorders unto themselves.

The NIH has recognized this for some time and developed a new framework for thinking about mental illnesses—the Research Domain Criteria (RDoC). The RDoC starts fresh, ignoring our current diagnostic labels and classifications. Instead, the framework focuses on domains of functioning—emotion, cognition, motivation, and social behavior. It assumes ranges in these constructs from normal to abnormal, and it encourages researchers to explore these constructs from a perspective other than a diagnostic label. At one point, proponents of the RDoC were calling for a complete overhaul of our current psychiatric diagnostic criteria. Changing psychiatry and the mental health field, however, is no easy feat, so our current diagnostic criteria remain, despite all the known flaws. RDoC remains only in the realm of research at this point. However, for our purposes, I am going to use this model to define mental illness in the context of the brain energy theory.

It starts by setting aside DSM-5 diagnostic labels and focusing instead on symptoms. This doesn’t mean that some of the diagnoses aren’t useful. Many are. Our current diagnostic labels simply describe some of the more common ways that the brain malfunctions. After all, the brain works, or fails to work, in predictable ways, and we can use those common narratives to our benefit.

The human brain is like a machine—a very sophisticated and complicated machine, but a machine nonetheless. It has many parts all designed to do certain things. Some are fairly straightforward, such as making our muscles move or sensing what we feel or see. Other functions of the brain are more complicated, like sophisticated computer algorithms that are triggered in certain situations. In one way or another, all these brain functions can be tied to helping us survive, adapt to our environments, or reproduce.

Given that the human brain has billions, if not trillions, of cells, and that each cell is a complicated machine itself, we face a potentially overwhelming problem: with so many cells, it seems there’s an almost infinite number of ways that all of these “parts” could malfunction. For better or worse, this is where the mental health field has been focused, with researchers trying to understand how the machine works, step-by-step. It’s an overwhelming task, the notion of wholly mapping something as complicated as the human brain, and waiting for this work to be finished has arguably limited our progress in better understanding and treating mental illness.

But it doesn’t have to be so complicated. It turns out that all symptoms of mental illness actually correspond to normal mental states or brain functions, but gone awry: present when they should not be, absent when they should be present, or more or less active or persistent than is appropriate. These brain functions include things that relate to emotions, cognition, behavior, and motivation. As I will discuss, even some of the more bizarre-seeming symptoms of mental illness, such as delusions and hallucinations, can be tied to normal brain functions. Although we don’t know precisely how all of these functions work, we know they exist. That’s enough for our purposes here.

Let’s start with a simple definition, then: Mental illness is when the brain is not working properly. Normal brain functions are either overactive, underactive, or absent. An easy example is having a panic attack for no clear reason. The panic system is beneficial when facing danger. It gets us moving. When it gets triggered for no clear reason, it’s dysfunctional and maladaptive. Sometimes the opposite can occur—brain functions that fail to activate in the right situations. Consider memory impairment in someone with dementia or a lack of social skills in someone with autism.

When it comes to symptoms of mental illness, many people would say that they can’t possibly correspond to normal brain functions. It can seem like somehow the brain is doing unique and highly unusual things for no clear reason. I look at it differently. Like the parts of any machine, the parts of the brain are either working or they aren’t. If they perform their usual function, but get turned on at the wrong time, it can result in symptoms that seem bizarre. The same is true when normal brain functions fail to activate, or if two unrelated brain functions are mistakenly occurring at the same time.

A Simple Example: Three Cars

Let me use an analogy to explain how I think about the way people with mental illness differ from those who are having “normal” stress reactions, even though their symptoms can be the same and they can both lead to poor health outcomes. I’ll describe three cars. Each is the same make and model, so in theory, they should have the same lifespan and overall “health.” Each represents a human being.

Car A lives in California, where the skies are blue, and the roads are in great condition. The owner doesn’t drive much—maybe twice a week. Car A is housed in a garage and gets regular maintenance. Car A is living the good life!

Car B lives in the mountains of New Hampshire, where the winters can be fierce, and the back roads are filled with potholes. The owner drives the car every day and doesn’t have a garage to store it in. When winter comes, Car B gets snow tires, and sometimes even snow chains. In a blizzard, Car B is using its headlights, windshield wipers, blinkers, snow tires and chains, and its four-wheel drive system. The brakes are applied often so that the driver doesn’t lose control. In these situations, Car B is getting very low gas mileage compared to Car A. Car B also has more maintenance problems, given the harsh winter environment and difficult driving conditions. In the end, Car B has more “health problems” and ends up living a shorter life than Car A.

Cars A and B are “normal”—they are both doing what they are supposed to, given the environmental circumstances they’re in. Neither has a disorder. Car B has more health problems and ends up living a shorter life, but given the adversity it faces, this is normal. The adaptations it uses, such as snow tires and chains, four-wheel drive, and frequent braking, are like stress responses—depression, anxiety, fear, anger. They help Car B navigate its difficult environment and they serve extraordinarily useful purposes. Without them, Car B would be much worse off.

Now let me tell you about the third car. Car C lives in Indiana, where the weather is less harsh than New Hampshire, and the roads are in decent shape. It gets driven five days a week, sometimes in good weather and sometimes in bad. But Car C has problems. It turns on its windshield wipers and blinkers even in sunny weather. The wiper blades are worn thin because they get used so much. They end up scratching the windshield. Car C sometimes uses its four-wheel drive and travels only twenty-five miles per hour on the highway, even though it’s sunny and all the other cars are going sixty. When Car C drives at night, it doesn’t turn on its lights, even though they are needed. Car C has a disorder comparable to a mental illness. Although it has the exact same features and adaptive strategies as Cars A and B, it is using some of them at the wrong times and under the wrong circumstances. Meanwhile, it’s failing to use others that it should be using. Car C ends up needing quite a bit of maintenance. It also gets into traffic accidents. Car C’s disorder is seriously affecting its health and safety and impacting its ability to get along with other cars on the road. Car C ends up dying an early death.

So . . . Cars A and B are “normal,” and Car C has a disorder.

People who are struggling with adversity, like Car B, often need help, even if their brains are not malfunctioning. Their biology is responding to their adverse life experiences in “normal,” predictable, and adaptive ways. To aid them, we need to change their environments or help them respond optimally to harsh conditions. For the most part, these are societal factors—things like war, poverty, food insecurity, abuse, systemic racism, homophobia, misogyny, sexual harassment, anti-Semitism, and many other societal “blizzards.” Changing society so that these blizzards no longer exist is the ideal way to deal with these issues. In the meantime, helping people cope as best as possible can also be helpful.

The brains of people with mental disorders are malfunctioning. They are doing things at the wrong times or with the wrong intensity, or they are failing to do things that they should be doing—as in the case of Car C. You don’t need to know precisely how these work in order to determine if there is a problem or not, just like you don’t need to fully understand the inner workings of a car and its windshield wiper system to know if there is a problem or not. I imagine you’re thinking that the problem with Car C isn’t with the car itself, but with the driver of Car C. In fact, you’re correct. I’ll get to that soon enough.

It’s important to point out that prolonged or extreme stress can lead to a disorder as well. At some point, Car B could easily develop maintenance problems that result in adaptive strategies no longer working—maybe the lights stop working or the windshield wipers get worn thin and are no longer effective (underactive functions). Or the blinkers won’t turn off (overactive function). At that point, Car B would also have a disorder.

A Human Example: Pain

Now I’ll try to show you that this really does happen in the human body by focusing on an easy, straightforward example—pain. Since pain is controlled by nerve cells and brain regions, it serves as a perfect example for most of the mental symptoms I’ll discuss.

Pain is a normal, healthy experience for humans—even though it is quite unpleasant. It saves our lives. It protects us from injuring ourselves. Pain is controlled by pain receptors, a nerve that goes to the spinal cord, another nerve that goes up to the brain, and then the regions of the brain that sense and process pain. The function and dysfunction of these neurons and brain regions gives us a simple framework that will help us better understand mental disorders.

Broadly speaking, disorders of the pain system can be lumped into three categories based on the function of the cells in the pain system—overactive, underactive, and absent.

These three scenarios—overactivity, underactivity, and absence of function —are all disorders. The pain system isn’t working correctly.

In some cases, it can be difficult to draw a line between normal pain and a pain disorder. One example is a herniated disc in the lower back causing pain. When the disc first becomes herniated, it’s not a disorder. The pain system is doing what it is supposed to do. If the pain goes on for a prolonged period of time, however, even after surgery and multiple medications, at some point we label it a pain disorder. What makes it a disorder? The nerves can become injured from the pressure of the herniated disc. These injured nerves can become hyperexcitable. They can send pain signals too often or too intensely. The point at which the pain goes from a normal response to a disorder is difficult, if not impossible, to distinguish based on current diagnostic tests. In some cases, it’s not clear whether it’s normal or a disorder. However, when the pain becomes chronic, severe, and unprovoked, we call it a disorder.

Regardless of whether pain is a normal response to an injury or a pain disorder, treating the pain is appropriate all the time. For example, we all know that people will feel pain when they get surgery. It’s normal and expected. However, we still treat it to alleviate suffering.

This distinction between normal and abnormal is important. Doctors who treat pain need to have good clinical skills. They need to understand the many reasons that someone might be experiencing pain. They need to evaluate their patients for these causes before assuming that they have a pain disorder. If a patient comes in with foot pain, it might be due to a sprain, a muscle spasm, a broken bone, or a piece of glass wedged in the skin. Each cause requires very different treatments. Treating the pain as though it is due to pain disorder might bring some relief, but it won’t solve the problem. In fact, the problem may get worse. However, if no obvious causes for foot pain are present, the doctor might then diagnose a pain disorder. This same type of detailed cause-and-effect assessment is necessary when evaluating people for mental disorders. Again, helping people cope with adversity is very different than treating a malfunctioning brain.

Back to Defining Mental Illness

Here’s our new, simplified definition of mental illness: A mental illness is when the brain is not working properly. Now let’s expand on that definition: A mental illness is when the brain is not working properly over a period of time, and this causes mental symptoms, which lead to suffering or impairment in functioning.

Although this is a fairly short and concise definition, every part matters, and no part can be taken out of context. This definition includes four necessary components:

Although these might seem like simple concepts, they can quickly get complicated.

The first component of this definition—the brain is not working properly—sounds straightforward. But it’s actually difficult to measure and assess based on current technologies, just like pain. We have many tests that can measure brain health and function, such as EEGs and neuroimaging studies. However, none of them is sensitive and specific enough to accurately diagnose a mental disorder. Measuring the function of microscopic brain regions is difficult. So, in the real world, how do we know if the brain isn’t working properly?

That leads us to the second component of the definition—this results in mental symptoms. Symptoms are the best indicator of abnormal brain function. However, like pain, when it comes to symptoms of mental illness, most can be normal, healthy brain functions in the right circumstances. Even something like hallucinations can occur in most people in the right circumstances. We all have hallucinations when we dream—we see things and hear things that aren’t there. When these things occur at the wrong time or when they fail to activate at the right time, they might represent a disorder. We can categorize the symptoms into the same three basic categories I used for pain—overactivity, underactivity, and absence of function.

Component three—this malfunction occurs over a period of time—reinforces that the duration of symptoms matters. All of our brains fail to work perfectly at least some of the time, and this results in what we might call symptoms. Most of us have occasional lapses in our memory. Sometimes, we think we hear a noise, but no one else hears it. Sometimes, we “wake up on the wrong side of the bed” and feel depressed for no clear reason. These are examples of the brain not working properly. These are not mental illnesses but common occurrences that can happen due to a variety of circumstances—a bad night’s sleep, an extraordinarily stressful situation, use of alcohol or drugs, or just having a bad day. These are usually short-lived experiences (also relating to metabolism) with an easy brain-body fix. Mental illnesses need to be persistent problems with brain function that result in symptoms. The persistence of symptoms is currently part of our diagnostic process in the mental health field, but the amount of time varies by diagnosis.

That brings us to component four of our definition: the symptoms cause suffering or impairment in functioning. We all have changes in emotions, cognition, motivation, and behaviors over the course of our lives. We learn. We grow. We meet new people and make changes. We go through challenging experiences. We suffer losses and setbacks. These fluctuations alone are not mental illness. Only when a person is distressed by these changes in an unusual way, or the changes prevent them from functioning in life, do we begin to consider the possibility of a mental illness. There is no question that this part of the definition is tricky, and the debates around the issue of suffering and impairment in functioning are complicated. Two issues are particularly important:

These nuanced dilemmas sometimes make it difficult, if not impossible, to distinguish between being different and living in an unforgiving and rigid society versus having a mental illness. The mental health field has changed its stance around issues like this over the years, such as labeling homosexuality a disorder at one point in time and then reversing that decision.

Symptoms of Mental Illness

Now that we’ve arrived at and unpacked a new definition of mental illness, let me put it into action by outlining three broad scenarios that can produce symptoms of mental illness. They follow the model that I outlined for disorders of the pain system—brain functions that are overactive, underactive, or absent.

Overactive Brain Functions

Overactivity or hyperexcitability of brain cells and networks has been documented in many mental disorders. When thinking about this phenomenon, we are looking for symptoms or brain functions that are occurring more often or more intensely than they should be, or at the wrong time.

Fear and anxiety symptoms can result from hyperexcitability of the amygdala—one of the regions of the brain implicated in the fear response. These neurons may fire out of turn or not stop firing, which causes anxiety symptoms at inappropriate times or an exaggerated fear response.

Obsessions and compulsions can result from hyperexcitable cells and networks in the brain areas associated with grooming and checking behaviors. We all normally groom ourselves and check things. OCD occurs when these systems are overactive.

Psychotic symptoms, such as hallucinations and delusions, are found in many mental and neurological disorders. They also occur in many people who never get diagnosed with any disorder.

The precise brain cells and regions that cause psychotic symptoms are currently unknown, despite decades of intensive research looking for them. Nonetheless, there are a few ways that we can think about what might be happening in the brain.

The easiest way to understand psychotic symptoms is hyperexcitability of brain cells that process perceptions. For example, if the brain cells and networks that perceive sound are hyperexcitable, people will hear something that isn’t there—an auditory hallucination. Neurosurgeons can make people “hallucinate” by stimulating brain areas with an electrode. Hyperexcitable cells would be doing essentially the same thing.

The problem might not be in the neurons that perceive sound but in other neurons that regulate them and slow them down. There are a group of neurons called “cortical interneurons.” These neurons are known to be inhibitory, as they secrete gamma-aminobutyric acid, or GABA, a neurotransmitter that slows activity in its target cells. Abnormalities in the function of these neurons have been found in many disorders, including schizophrenia, Alzheimer’s disease, epilepsy, and autism. This lack of inhibition would result in overactivity of the neurons they are supposed to be inhibiting.

Another possibility is that psychotic symptoms are related to the sleep systems in the brain. As I mentioned, we all have hallucinations and delusions every day—in our sleep. When we dream, we hear things and see things that aren’t there. We can believe wild and crazy things. Many people have nightmares that include being chased or persecuted. If these experiences occur during sleep, they are just bad dreams, not mental disorders. It’s possible that the same brain cells and networks that create these experiences at night are hyperexcitable and firing erroneously during the day in people with mental disorders.

For some delusions that can seem bizarre, such as Capgras syndrome in which people believe that their loved ones have been replaced by imposters, we actually do know some of the specific brain networks involved in this process.¹⁰ These areas of the brain appear to be overactive and/or underactive.

One important observation is that hallucinations are not as uncommon as most people would think. Researchers have found that 12 to 17 percent of children ages nine to twelve and 5.8 percent of adults hallucinate during the day.¹¹ Additionally, 37 percent of adults experience hallucinations when they are falling asleep, also known as “hypnagogic hallucinations.”¹² Most of these people are not diagnosed with mental disorders.

Underactive Brain Functions

Underactive brain cells and brain networks have been documented in many mental disorders. This concept easily explains at least some of the symptoms that we see. I distinguish underactive function from the absence of function because underactive function implies the cells are still alive and able to work at least some of the time. This is important, as it means that symptoms will wax and wane. Sometimes things can seem normal, and other times the person can have symptoms. Here are some examples:

Absence of Specific Brain Functions

Some mental disorders involve permanent changes in brain cells and connections. There are two primary causes of this—developmental problems and cell death. These problems are often associated with neurodevelopmental and neurodegenerative disorders, respectively. Cell death can also occur from things like a stroke or brain injury, which are different from neurodegenerative disorders, but these, too, can also result in mental symptoms.

There are many neurodevelopmental disorders. Autism is one example. Neurons and/or connections between neurons appear to be missing or at least different.

Neurodegenerative disorders, such as Alzheimer’s disease, are associated with brain shrinkage and death of neurons. Once neurons die, there is usually no way to bring them back.

In both cases, cells or connections that are supposed to be present are not, so the brain is unable to perform these functions. Symptoms due to these permanent changes are always present. They don’t wax and wane. The social deficits seen in autism are fixed. At least some of the cognitive deficits seen in Alzheimer’s disease are also fixed. These don’t change from day to day. However, both autism and Alzheimer’s disease are also associated with ongoing mental symptoms that do wax and wane—anxiety, psychosis, and mood changes, to name a few.

These three scenarios—overactive, underactive, and absent brain functions—can account for all symptoms of mental disorders. However, there are two additional situations that are worth mentioning, because at first glance, they may not appear to fit neatly into these categories: multifaceted brain adaptations and behavioral disorders.

Multifaceted Brain Adaptations

The brain sometimes has complicated responses to situations that involve multiple symptoms, with some of them representing activation of some brain functions and inactivation of others. I will discuss depression, hypomania, and the trauma response. All of these can be normal and adaptive when they occur at the right times under the right circumstances. They are similar to the activation of the sympathetic and parasympathetic nervous systems, which involve a complicated array of brain and body functions, some that get turned on and others that get turned off.

Depression is a normal reaction to many stressors, adversities, and losses. Almost everyone has been depressed at least once. It usually doesn’t last unrelentingly for two or more weeks, but it’s a normal brain response. Although it commonly includes changes in mood, energy, appetite, and sleep, these changes can be very different in different people. Some people appear to have overactivity of the appetite system and others appear to have underactivity, resulting in eating too much or too little, respectively. Likewise, some people can sleep too much and others can’t sleep enough. Distilling depression into distinct symptoms, some that represent overactive or underactive brain regions, is likely to be the most effective and accurate way to understand depression, even though depression often involves many symptoms.

Hypomania in many ways is the opposite of depression—people can feel great or euphoric, have increased energy, be more productive, and even get by on less sleep. This can also be normal. In fact, if it occurs in isolation, it’s not a diagnosable disorder according to DSM-5. Most people have experienced symptoms of hypomania at some point or another in life. This commonly occurs when people fall in love, but it can also occur when people are excited about a project or an accomplishment, or when they have a spiritual awakening. Again, it may not last five or more days, but it can occur, which suggests that these brain functions are hardwired into all of our brains.

The trauma response is also normal. These symptoms include flashbacks and nightmares, avoidance of situations that remind the person of the event, negative effects on mood and thinking (similar to depression), trouble sleeping, being on edge and hyperalert, and other symptoms. One research group studied women shortly after being raped and found that 94 percent of them had these types of symptoms in the first weeks.¹⁴ So, all of these responses can be “normal.”

These multifaceted brain adaptations become disorders when they are overactive. They can be activated at the wrong time, last too long, or result in excessive or exaggerated symptoms. In some cases, they can be activated out of the blue for no clear reason—a hyperexcitable activation of the system. In other cases, they can be activated for a clear reason, such as a major stressor in life, but then they fail to inactivate after an appropriate amount of time. They become “stuck” in an “on” position when they should be turning off. This is similar to hyperexcitable pain cells in many pain disorders. Sometimes they can fire for no clear reason, but other times, the slightest injury or just moving the wrong way can trigger pain.

Behavioral Disorders

Some disorders are seen primarily as behavioral—in particular, substance use and eating disorders. These deserve special attention as well. Recall that they show strong bidirectional relationships with all mental disorders. I have said that mental disorders can be understood broadly as overactive, underactive, or absent brain functions. But these are behaviors . . . ones that people “choose” to engage in. What do these behaviors have to do with the brain malfunctioning?

There are three ways to think about it. The first is that eating and using addictive substances are behaviors that are controlled by our brains. There are clear pathways that control cravings, appetite, motivation, self-control, impulsivity, and novelty seeking. So, in some cases, if these parts of the brain are overactive or underactive, they might drive people to engage in these behaviors, which can lead to problems. The second possibility is that people may have symptoms of other mental disorders (due to overactive or underactive brain regions) and use alcohol, drugs, or change eating behaviors to cope with those symptoms. This is commonly referred to as the self-medication hypothesis. The third possibility is that some people can be perfectly fine and “normal” and begin to engage in these behaviors. Some can start using drugs or alcohol due to peer pressure alone. A person can start dieting due to peer pressure alone. As I will discuss later, all of these behaviors can have powerful effects on metabolism and the brain. They can lead to metabolic abnormalities, which can lead to overactivity and underactivity of specific brain functions, that can then trap people in vicious cycles—ones that we call eating disorders and substance use disorders.

A Complex Puzzle

One of the challenges in identifying what causes mental illness is that the findings I’ve mentioned here, such as reduced default-mode network activity leading to depression, are not consistent across people with the same disorder, or even in the same person at different times. Other than in cases of developmental abnormalities or cell death, the symptoms wax and wane, and so can the neuroscience findings. That’s why we don’t yet have diagnostic tests. The developmental abnormalities are not consistent for specific disorders, either. They can affect a wide range of cell types and brain regions in different people, even people diagnosed with the same disorder. When looking at brain changes and the way the brain functions in mental illness, heterogeneity and inconsistent findings are the name of the game.

That’s a lot to account for. It’s no wonder that the puzzle of mental illness has been so difficult to solve. What makes different parts of the brain overactive or underactive, leading to symptoms of mental illness? What makes the symptoms wax and wane? What exactly is causing these developmental abnormalities or areas of cell shrinkage and death? Why are they different in different people? All of these questions need to be addressed by any theory that tries to account for all mental disorders. I’m excited to share with you that the brain energy theory can do it. And it’s all through one common pathway.