The following information comes from the National Institute of Mental Health.
Mental disorders are common. You may have a friend, colleague, or relative with a mental disorder, or perhaps you have experienced one yourself at some point. Such disorders include depression, anxiety disorders, bipolar disorder, attention deficit hyperactivity disorder (ADHD), and many others.
Some people who develop a mental illness may recover completely; others may have repeated episodes of illness with relatively stable periods in between. Still others live with symptoms of mental illness every day. They can be moderate, or serious and cause severe disability.
Through research, we know that mental disorders are brain disorders. Evidence shows that they can be related to changes in the anatomy, physiology, and chemistry of the nervous system. When the brain cannot effectively coordinate the billions of cells in the body, the results can affect many aspects of life.
Scientists are continually learning more about how the brain grows and works in healthy people, and how normal brain development and function can go awry, leading to mental illnesses.
How the Brain Works
Everything we do relies on neurons communicating with one another. Electrical impulses and chemical signals carrying messages across different parts of the brain and between the brain and the rest of the nervous system. When a neuron is activated a small difference in electrical charge occurs. This unbalanced charge is called an action potential and is caused by the concentration of ions (atoms or molecules with unbalanced charges) across the cell membrane. The action potential travels very quickly along the axon, like when a line of dominoes falls.
When the action potential reaches the end of an axon, most neurons release a chemical message (a neurotransmitter) which crosses the synapse and binds to receptors on the receiving neuron’s dendrites and starts the process over again. At the end of the line, a neurotransmitter may stimulate a different kind of cell (like a gland cell), or may trigger a new chain of messages.
Neurotransmitters send chemical messages between neurons. Mental illnesses, such as depression, can occur when this process does not work correctly. Communication between neurons can also be electrical, such as in areas of the brain that control movement. When electrical signals are abnormal, they can cause tremors or symptoms found in Parkinson’s disease.
- Serotonin—helps control many functions, such as mood, appetite, and sleep. Research shows that people with depression often have lower than normal levels of serotonin. The types of medications most commonly prescribed to treat depression act by blocking the recycling, or reuptake, of serotonin by the sending neuron. As a result, more serotonin stays in the synapse for the receiving neuron to bind onto, leading to more normal mood functioning.
- Dopamine—mainly involved in controlling movement and aiding the flow of information to the front of the brain, which is linked to thought and emotion. It is also linked to reward systems in the brain. Problems in producing dopamine can result in Parkinson’s disease, a disorder that affects a person’s ability to move as they want to, resulting in stiffness, tremors or shaking, and other symptoms. Some studies suggest that having too little dopamine or problems using dopamine in the thinking and feeling regions of the brain may play a role in disorders like schizophrenia or attention deficit hyperactivity disorder (ADHD).
- Glutamate—the most common neurotransmitter, glutamate has many roles throughout the brain and nervous system. Glutamate is an excitatory transmitter: when it is released it increases the chance that the neuron will fire. This enhances the electrical flow among brain cells required for normal function and plays an important role during early brain development. It may also assist in learning and memory. Problems in making or using glutamate have been linked to many mental disorders, including autism, obsessive compulsive disorder (OCD), schizophrenia, and depression.
Just as many neurons working together form a circuit, many circuits working together form specialized brain systems. We have many specialized brain systems that work across specific brain regions to help us talk, help us make sense of what we see, and help us to solve a problem. Some of the regions most commonly studied in mental health research are listed below.
- Amygdala—The brain’s “fear hub,” which activates our natural “fight-or-flight” response to confront or escape from a dangerous situation. The amygdala also appears to be involved in learning to fear an event, such as touching a hot stove, and learning not to fear, such as overcoming a fear of spiders. Studying how the amygdala helps create memories of fear and safety may help improve treatments for anxiety disorders like phobias or post-traumatic stress disorder (PTSD).
- Prefrontal cortex (PFC)—Seat of the brain’s executive functions, such as judgment, decision making, and problem solving. Different parts of the PFC are involved in using short-term or “working” memory and in retrieving long-term memories. This area of the brain also helps to control the amygdala during stressful events. Some research shows that people who have PTSD or ADHD have reduced activity in their PFCs.
- Anterior cingulate cortex (ACC)— the ACC has many different roles, from controlling blood pressure and heart rate to responding when we sense a mistake, helping us feel motivated and stay focused on a task, and managing proper emotional reactions. Reduced ACC activity or damage to this brain area has been linked to disorders such as ADHD, schizophrenia, and depression.
- Hippocampus—Helps create and file new memories. When the hippocampus is damaged, a person can’t create new memories, but can still remember past events and learned skills, and carry on a conversation, all which rely on different parts of the brain. The hippocampus may be involved in mood disorders through its control of a major mood circuit called the hypothalamic-pituitary-adrenal (HPA) axis.