According to the National Institute of Mental Health, about 2.4 million American adults have some form of schizophrenia, a disorder that affects perception of reality.

Schizophrenia subtypes include:

paranoid , which causes people to believe they are being singled out for harm

, which causes people to believe they are being singled out for harm disorganized , which causes garbled speech and thought patterns and frequently causes the inability to handle basic daily activities (bathing, dressing appropriately for the weather) by oneself

, which causes garbled speech and thought patterns and frequently causes the inability to handle basic daily activities (bathing, dressing appropriately for the weather) by oneself catatonic , which ranges from the inability to move or speak on one extreme to being overly excitable (frenzied pacing, walking in circles) for no obvious reason on the other

, which ranges from the inability to move or speak on one extreme to being overly excitable (frenzied pacing, walking in circles) for no obvious reason on the other undifferentiated , in which symptoms are not well enough defined to permit classification into one of the other categories

, in which symptoms are not well enough defined to permit classification into one of the other categories residual, when the illness is no longer in an acute phase.

Schizophrenia symptoms generally first appear between ages 16 and 30, though men can have symptoms — such as hallucinations and delusions — before women do. Auditory hallucinations, in which sufferers hear voices in their heads, and unrealistic beliefs, such as possession of superpowers, are most common.

Schizophrenia also can affect cognition. For example, disorganized thinking can make it hard to connect thoughts logically. Other cognitive symptoms include problems with attention and working memory.

The exact cause of schizophrenia is unknown, though genetics and environmental factors may play a role. For example, altered brain structures, such as having less gray matter than average, may contribute to the onset of the disorder. Altered brain chemistry, specifically due to the neurotransmitter dopamine, also may be a factor.

The Dopamine Theory of Schizophrenia

Pharmacological treatments support the idea that an overactive dopamine system may result in schizophrenia: Medications that block dopamine receptors, specifically D2 receptors, reduce schizophrenia symptoms.

The brain regions known as the thalamus and the striatum are affected by dopaminergic activity. Manzano et al. explain that schizophrenia results in altered levels of D2 binding potential in those two regions of the brain. For example, the authors note that schizophrenia patients who do not take antipsychotic medications have a lower thalamic D2 binding potential. In addition, untreated schizophrenia patients have a higher number of D2 receptors in the striatum.

Creativity and Schizophrenia

Divergent thinking, which affects the way individuals arrive at ideas, also is affected by dopaminergic activity, according to Manzano et al. For example, when testing divergent thinking, participants are given an object, such as a stone, and asked different ways that it could be used. More creative people come up with more uses for the object.