Delusion refers to a fixed belief that is firmly held despite solid evidence to the contrary.

The cause of delusion is not clear but genetic, neurological and biochemical factors have been suggested to play a role in the development of the condition.

Some research suggests that delusions may be caused by an imbalance in neurotransmitters, the brain’s chemical messengers. Some examples of other factors that may be involved include social isolation, widowhood, drug abuse, low socioeconomic status and stress.

Delusional disorder is a condition that is considered to lie within the same spectrum as schizophrenia, although individuals who suffer from delusion generally present with less severe symptoms and dysfunction.

One theory that has been developed to explain delusion is the genetic theory which states that individuals with close family members who have delusional disorder are more likely to develop the condition. Another theory is that some people have dysfunctional cognitive processing which means their explanations for the way their lives unfold are distorted and illogical. A third suggested theory is that delusions may be motivated or defensive, meaning that individuals who are already predisposed to delusional thinking start to experience delusions when life events or self-esteem issues become challenging to cope with. In these situations most sufferers tend to blame others for their difficulties, stress and failure and try to hold on to a positive opinion of themselves.

One study by Orrin Devinsky from the NYU Langone Medical Center demonstrated a particular pattern of injury in the frontal lobe and right hemisphere of the brain in individuals who have some forms of delusion. Devinksy suggests that cognitive deficits resulting from injury to the brain in the right hemisphere cause an over-compensation in the left hemisphere that leads to delusions.

Delusion is also more common among individuals with hearing or vision problems.