The Science of Mental Illness
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The Science of Mental Illness

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Information about Mental Illness and the Brain (Page 2 of 3)

Mental health professionals evaluate symptoms to make a diagnosis of mental illness.

5.2 Investigating Brain Function

Mental health professionals base their diagnosis and treatment of mental illness on the symptoms that a person exhibits. The goal for these professionals in treating a patient is to relieve the symptoms that are interfering with the person’s life so that the person can function well. Research scientists, on the other hand, have a different goal. They want to learn about the chemical or structural changes that occur in the brain when someone has a mental illness. If scientists can determine what happens in the brain, they can use that knowledge to develop better treatments or find a cure.

The techniques that scientists use to investigate the brain depend on the questions they are asking. For some questions, scientists use molecular or biochemical methods to investigate specific genes or proteins in the neurons. For other questions, scientists want to visualize changes in the brain so that they can learn more about how the activity or structure of the brain changes. Historically, scientists could examine brains only after death, but new imaging procedures enable scientists to study the brain in living animals, including humans. It is important to realize that these brain imaging techniques are not used for diagnosing mental illness. Mental illnesses are diagnosed by the set of symptoms that an individual exhibits. The imaging techniques described in the following paragraphs would not enable the mental health professional to diagnose or treat the patient more effectively. Some of the techniques are also invasive and expose patients to small amounts of radiation. Research studies using these tests are generally not conducted with children or adolescents.

One extensively used technique to study brain activity and how mental illness changes the brain is positron emission tomography (PET). PET measures the spatial distribution and movement of a radioactive chemical injected into the tissues of living subjects. Because the patient is awake, the technique can be used to investigate the relationship between behavioral and physiological effects and changes in brain activity. PET scans can detect very small (nanomolar) concentrations of tracer molecules and achieve spatial resolution of about 4 millimeters. In addition, computers can reconstruct images obtained from a PET scan in two or three dimensions.

PET requires the use of compounds that are labeled with positron-emitting isotopes. A positron has the same mass and spin as an electron but the opposite charge; an electron has a negative charge and a positron has a positive charge. A cyclotron accelerates protons into the nucleus of nitrogen, carbon, oxygen, or fluorine to generate these isotopes. The additional proton makes the isotope unstable. To become stable again, the proton must break down into a neutron and a positron. The unstable positron travels away from the site of generation and dissipates energy along the way. Eventually, the positron collides with an electron, leading to the emission of two gamma rays at 180 degrees from one another. The gamma rays reach a pair of detectors that record the event. Because the detectors respond only to simultaneous emissions, scientists can precisely map the location where the gamma rays were generated. The radioactive chemicals used for PET are very short lived. The half-life (the time for half of the radioactive label to disintegrate) of the commonly used radioisotopes ranges from approximately two minutes to less than two hours, depending on the specific compound. Because a PET scan requires only small amounts (a few micrograms) of short-lived radioisotopes, this technique can be used safely in humans.

photo of a scientist looking at PET scans
Figure 5. Scientists use a variety of imaging techniques to investigate brain structure and function.

PET scans can answer a variety of questions about brain function, including where the neurons are most active. Scientists use different radiolabeled compounds to investigate different biological questions. For example, radiolabeled glucose can identify parts of the brain that become more active in response to a specific stimulus. Active neurons metabolize more glucose than inactive neurons. Active neurons emit more positrons, and this shows as red or yellow on PET scans compared with blue or purple in areas where the neurons are not highly active. (Different computer enhancement techniques may use a different color scheme, but the use of a spectrum with red indicating high activity and blue indicating low activity is common.) Scientists can use PET to measure changes in the activity of specific brain areas in a person who has a mental illness. Scientists can also investigate how the mentally ill brain changes after a person receives treatment.

PET imaging is not the only technique that researchers use to investigate how mental illness changes the brain. Different techniques provide different information to scientists. Another important technique is magnetic resonance imaging (MRI). Unlike PET, which reveals changes in activity level, MRI is used to look at structural changes in the brain. For example, MRI studies reveal that the ventricles, or spaces within the brain, are larger in individuals who have schizophrenia compared with those of healthy individuals.

Other techniques that scientists use to investigate function in the living brain include single photon emission computed tomography (SPECT), functional magnetic resonance imaging (fMRI), and electroencephalography (EEG). Each technique has its own advantages, and each provides different information about brain structure and function. Scientists often use more than one technique when conducting their research.

Scientists believe that mental illnesses result from problems with the communication system in the brain.

6 The Causes of Mental Illnessesa

At this time, scientists do not have a complete understanding of what causes mental illnesses. If you think about the structural and organizational complexity of the brain together with the complexity of effects that mental illnesses have on thoughts, feelings, and behaviors, it is hardly surprising that figuring out the causes of mental illnesses is a daunting task. The fields of neuroscience, psychiatry, and psychology address different aspects of the relationship between the biology of the brain and individuals’ behaviors, thoughts, and feelings, and how their actions sometimes get out of control. Through this multidisciplinary research, scientists are trying to find the causes of mental illnesses. Once scientists can determine the causes of a mental illness, they can use that knowledge to develop new treatments or to find a cure.

6.1 The Biology of Mental Illnesses

Most scientists believe that mental illnesses result from problems with the communication between neurons in the brain (neurotransmission). For example, the level of the neurotransmitter serotonin is lower in individuals who have depression. This finding led to the development of certain medications for the illness. Selective serotonin reuptake inhibitors (SSRIs) work by reducing the amount of serotonin that is taken back into the presynaptic neuron. This leads to an increase in the amount of serotonin available in the synaptic space for binding to the receptor on the postsynaptic neuron. Changes in other neurotransmitters (in addition to serotonin) may occur in depression, thus adding to the complexity of the cause underlying the disease.

Scientists believe that there may be disruptions in the neurotransmitters dopamine, glutamate, and norepinephrine in individuals who have schizophrenia. One indication that dopamine might be an important neurotransmitter in schizophrenia comes from the observation that cocaine addicts sometimes show symptoms similar to schizophrenia. Cocaine acts on dopamine-containing neurons in the brain to increase the amount of dopamine in the synapse.

6.2 Risk Factors for Mental Illnesses

Although scientists at this time do not know the causes of mental illnesses, they have identified factors that put individuals at risk. Some of these factors are environmental, some are genetic, and some are social. In fact, all these factors most likely combine to influence whether someone becomes mentally ill.

Genetic, environmental, and social factors interact to influence whether someone becomes mentally ill.

Environmental factors such as head injury, poor nutrition, and exposure to toxins (including lead and tobacco smoke) can increase the likelihood of developing a mental illness.

Genes also play a role in determining whether someone develops a mental illness. The illnesses that are most likely to have a genetic component include autism, bipolar disorder, schizophrenia, and ADHD. For example, the observation that children with ADHD are much more likely to have a sibling or parent with ADHD supports a role for genetics in determining whether someone is at risk for ADHD. In studies of twins, ADHD is significantly more likely to be present in an identical twin than a fraternal twin. The same can be said for schizophrenia and depression. Mental illnesses are not triggered by a change in a single gene; scientists believe that the interaction of several genes may trigger mental illness. Furthermore, the combination of genetic, environmental, and social factors might determine whether a case of mental illness is mild or severe.

Figure 6
Figure 6. Scientists understand that mental illnesses are associated with changes in neurochemicals. For example, in people who have depression, less of the neurotransmitter serotonin (small circles) is released into the synaptic space than in people who do not have depression. Certain medications called selective serotonin reuptake inhibitors (SSRIs) relieve symptoms of depression by causing an increase in the amount of serotonin in the synaptic space.

Social factors also present risks and can harm an individual’s, especially a child’s, mental health. Social factors include

7 Treating Mental Illnessesb

At this time, most mental illnesses cannot be cured, but they can usually be treated effectively to minimize the symptoms and allow the individual to function in work, school, or social environments. To begin treatment, an individual needs to see a qualified mental health professional. The first thing that the doctor or other mental health professional will do is speak with the individual to find out more about his or her symptoms, how long the symptoms have lasted, and how the person’s life is being affected. The physician will also do a physical examination to determine whether there are other health problems. For example, some symptoms (such as emotional swings) can be caused by neurological or hormonal problems associated with chronic illnesses such as heart disease, or they can be a side effect of certain medications. After the individual’s overall health is evaluated and the condition diagnosed, the doctor will develop a treatment plan. Treatment can involve both medications and psychotherapy, depending on the disease and its severity.

At this time, most mental illnesses cannot be cured, but they can usually be treated effectively to minimize the symptoms and allow the individual to function in work, school, or social environments.

7.1 Medications

Medications are often used to treat mental illnesses. Through television commercials and magazine advertisements, we are becoming more aware of those medications. To become fully effective, medications for treating mental illness must be taken for a few days or a few weeks. When a patient begins taking medication, it is important for a doctor to monitor the patient’s health. If the medication causes undesirable side effects, the doctor may change the dose or switch to a different medication that produces fewer side effects. If the medication does not relieve the symptoms, the doctor may prescribe a different medication.2

pills of different shapes and sizes
Figure 7. Medicines are one part of an effective treatment plan for mental illnesses.

Sometimes, individuals who have a mental illness do not want to take their medications because of the side effects. It is important to remember that all medications have both positive and negative effects. For example, antibiotics have revolutionized treatment for some bacterial diseases. However, antibiotics often affect beneficial bacteria in the human body, leading to side effects such as nausea and diarrhea. Psychiatric drugs, like other medications, can alleviate symptoms of mental illness but can also produce unwanted side effects. People who take a medication to treat an illness, whether it is a mental illness or another disease, should work with their doctors to understand what medication they are taking, why they are taking it, how to take it, and what side effects to watch for.

Occasionally, the media reports stories in which the side effects of a psychiatric medication are tied to a potentially serious consequence, such as suicide. In these cases, it is usually very difficult to determine how much suicidal behavior was due to the mental disorder and what the role of the medication might have been. Medications for treating mental illness can, like other medications, have side effects. The psychiatrist or physician can usually adjust the dose or change the medication to alleviate side effects.

7.2 Psychotherapy

Psychotherapy is a treatment method in which a mental health professional (psychiatrist, psychologist, or other mental health professional) and the patient discuss problems and feelings. This discussion helps patients understand the basis of their problems and find solutions. Psychotherapy may take different forms. The therapy can help patients

Psychotherapy may occur between a therapist and an individual; a therapist and an individual and his or her family members; or a therapist and a group. Often, treatment for mental illness is most successful when psychotherapy is used in combination with medications. For severe mental illnesses, medication relieves the symptoms and psychotherapy helps individuals cope with their illness.3

Just as there are no medications that can instantly cure mental illnesses, psychotherapy is not a one-time event. The amount of time a person spends in psychotherapy can range from a few visits to a few years, depending on the nature of the illness or problem. In general, the more severe the problem, the more lengthy the psychotherapy should be.3

a Relevant to Lessons 2 and 3.

b Relevant to Lessons 4 and 5.


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