Reference delusions represent a common symptom in people diagnosed with schizophrenia. Patients who have delusions of reference may believe that neutral comments carry personal messages directed at them, which often come in negative forms. These communications can come from television, radio or pedestrians on the street. Messages can also come from objects or events that have no basis in reality. In addition to schizophrenia, symptoms can occur in patients with bipolar disorder, major depressive disorder, and dementia.

People who experience referral delusions absolutely believe these messages are real, which may include nonverbal cues from other people or real words. They may believe that the sole purpose of an event is specifically focused on revealing a missive to them. If the illusion involves an object, schizophrenics may believe it was placed there for the purpose of sending personal information, despite evidence to the contrary.

Delusions can be mood-linked or considered neutral. A schizophrenic suffering from depression may interpret delusions of reference with a sense of condemnation. If the patient suffers from a manic episode, the communication received can provoke a feeling of invincibility. When in a neutral state, the patient may feel that thoughts are entering their head.

One study found increased neural activity in various parts of the brain when reference delusions occurred. The researchers asked personal questions designed to provoke delusions and measure brain activity using MRI. Research results indicated that brain activity increased when patients strongly believed in delusions of reference. Generic and impersonal questions failed to get the same answers.

Delusions can focus on several themes, with persecutory delusions defining the most common symptom related to schizophrenia. These patients believe that someone wants to harm them when there is no evidence. They may think they are being followed or spied on as part of a conspiracy. Both delusions of persecution and delusions of reference fall into the category of non-bizarre symptoms, defined as probably not true but possible.

Bizarre delusions may include control delusions in which the patient believes that outside influences control his thoughts or actions. The patient may think that thoughts can be heard and manipulated by real or imaginary people, aliens or forces. Strange delusions cannot occur or be scientifically proven.

Other common delusions related to mental disorders include delusions of guilt and grandeur. A schizophrenic may believe he is responsible for a negative event when the patient had nothing to do with it. He or she may feel the need for punishment for imaginary sins. Delusions of grandeur usually give the patient a sense of remarkable power or talent without any evidence.