The brain is a complex grouping of nerve cells and other structures that help us think, react to the environment, make decisions and plans, and carry them out. In conjunction with the nervous system, some parts of our brain are responsible for our vital bodily functions, such as breathing and the heartbeat. Other parts of our brain control learning and memory, our senses (sight, smell, hearing, taste, and touch), and emotions.

To keep the many functions of the body and mind working properly, the billions of nerve cells in the brain (which are also called neurons) must communicate with each other and work together frequently. Brain chemicals called neurotransmitters help to send electrical signals or messages from one neuron to another. At any given moment, millions of these messages are transmitted throughout the brain, allowing it to process information and send instructions to various parts of the body. In response, we engage in a wide range of behaviors, some of which we are aware of and can control, like making choices, and some of which are more automatic, like breathing.

There are many conditions which can affect our brain health, and this can have a wide range of effects on our ability to function normally. Scientific advances in recent years have made it clear that the brain plays a central role in mental health. We understand mental illnesses as conditions that negatively affect a person's thoughts, emotions, and behaviors. Mental illness disrupts one's ability to relate to others and to function when meeting the demands of daily life.

Mental illnesses include mood disorders such as major depression and bipolar disorder, schizophrenia, and anxiety disorders, to name a few. Researchers studying the role of the brain in these illnesses have found strong evidence that imbalances in certain types of neurotransmitters can cause abnormalities in the communication among neurons. When this occurs, the brain may not send the proper instructions to the body, which may, in turn, lead to certain symptoms of mental illness.

In addition to imbalances in brain chemicals, changes in the size and shape of actual structures in the brain can also contribute to certain mental illnesses. These neurological abnormalities observed in people with some types of mental illnesses are a good demonstration of the overlap between the symptoms of neurological and psychiatric illnesses. Because of the prominent brain abnormalities that have been observed, certain conditions that are considered to be mental illnesses, such as schizophrenia have been theorized by some scientists to be neurological diseases.

Dementia is another excellent example of the overlap between brain abnormalities and psychiatric symptoms. As an illness with both neurological and psychological symptoms, dementia affects thoughts, personality, feelings, and behavior. The causes of dementia, although not fully understood, have been in large part, traced to structural and chemical deterioration in the brain. For this reason, various types of dementia are diagnosed and treated by teams of professionals that include both neurologists and psychologists, both of whom are trained to assess and treat illnesses that involve brain health.