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Mental Disorders

Mental disorders–also called psychiatric disorders–are illnesses or medical conditions that develop in or affect the brain. These medical conditions disrupt a person’s thinking, feeling, mood, daily functioning and ability to relate to others. The American Psychiatric Association developed a classification system called the Diagnostic and Statistical Manual of Mental Disorders (DSM) to assist physicians and other healthcare professionals in diagnosing mental disorders. The DSM lists the many different conditions that are recognized as mental illnesses. The more common types include:

  • anxiety disorders
  • mood disorders, e.g. depression
  • psychotic disorders, e.g., schizophrenia
  • eating disorders
  • impulse control and addiction disorders
  • personality disorders.

According to the National Institutes of Health, one in four adults–or nearly 60 million Americans–experience a mental health disorder in a given year. Anxiety disorders, including panic disorder, obsessive-compulsive disorder (OCD), post-traumatic stress disorder (PTSD), affect nearly 20 percent of adults, an estimated 40 million individuals. Major depression, bipolar disorder and schizophrenia are among the top 10 leading causes of disability in the United States. Symptoms of mental disorders, which can range from mild to severe, vary depending on the type of disorder.

The cause of most mental illnesses is not known, although it appears that many conditions are caused by a combination of genetic, biological, psychological and environmental factors. Mental illness is treatable; diagnosed individuals can experience relief from their symptoms by actively participating in an individual treatment plan.

Molecular Imaging and Mental Illness

According to the National Institute of Mental Health (NIMH), advanced research including molecular imaging of the brain is expanding our understanding or mental disorders. Unlike neurological disorders that are characterized by lesions in the brain, mental illnesses appear to be disorders within the circuits of the brain.

Brain circuits are interconnected brain cells, or neurons, that process information. Some neurons send messages in the form of a chemical signal (called a neurotransmitter) and others send an electrical signal. The constant exchange of messages between neurons, is called neurotransmission and involves these basic steps:

  • a neuron is activated
  • neuron sends a signal across the synapse, tiny gaps between two neurons
  • the neurotransmitter binds to the receptor of a receiving cell
  • during the binding process the neurotransmitter’s message is passed on.

Mental illnesses–as well as other brain disorders such as Parkinson’s disease–are linked to a disruption in brain circuitry. Many brain disorders, such as depression, are associated with either an excess or a shortage of neurotransmitters, such as serotonin, dopamine, noradrenaline and glutamate. An increase in dopamine concentration plays a role in the development of schizophrenia and new research found an association between PTSD and lower levels of a specific serotonin neurotransmitter.

Using SPECT and PET techniques to study neurotransmitters and receptors, researchers are gaining new insights into the biology and treatment of brain disorders. PET and SPECT have been applied most widely to the study of schizophrenia and to investigate the pathophysiology and treatment of depression. Molecular imaging techniques are also being used to study:

  • mood, addiction and other behavioral disorders
  • post traumatic stress disorder (PTSD)
  • traumatic brain injury.