Schizophrenia is one of several psychotic disorders described in the DSM. People with psychotic disorders lose contact with reality and often have delusions or hallucinations. People with schizophrenia have a wide range of symptoms, which can be classified into positive or negative symptoms.

Positive Symptoms

Positive symptoms involve the presence of altered behaviors. Examples of positive symptoms include delusions, hallucinations, disorganized speech, and disorganized behavior. Delusions are false beliefs that are strongly held despite contradictory evidence. Hallucinations are sensory or perceptual experiences that happen without any external stimulus. Hallucinations can occur in any sensory modality, but auditory hallucinations are most common in schizophrenia. Disorganized speech can also take many forms. For example, a person with schizophrenia may produce word salad, which consists of words and sentences strung together in an incoherent way. Examples of disorganized behavior include inappropriate gestures or laughter, agitated pacing, or unpredictable violence.

Negative Symptoms

Negative symptoms involve an absence or reduction of normal behavior. Negative symptoms include emotional flatness, social withdrawal, spare or uninflected speech, and lack of motivation.

Subtypes of Schizophrenia

Schizophrenia is classified into four subtypes, depending on the symptoms present at the time of evaluation:

  1. Paranoid type: Characterized by marked delusions or hallucinations and relatively normal cognitive and emotional functioning. Delusions are usually persecutory, grandiose, or both. Persecutory delusions involve a belief that one is being oppressed, pursued, or harassed in some way. Grandiose delusions involve the belief that one is very important or famous. This subtype usually happens later in life than the other subtypes. Prognosis may also be better for this subtype than for other subtypes.
  2. Disorganized type: Characterized by disorganized behavior, disorganized speech, and emotional flatness or inappropriateness.
  3. Catatonic type: Characterized by unnatural movement patterns such as rigid, unmoving posture or continual, purposeless movements, or by unnatural speech patterns such as absence of speech or parroting of other people’s speech.
  4. Undifferentiated type: Diagnosis given to a patient that does not meet criteria for paranoid, disorganized, or catatonic schizophrenia.

Etiology of Schizophrenia

As with other psychological disorders, researchers have studied the etiology of schizophrenia from different perspectives.

Biological Factors

Research suggests that genes, neurotransmitters, and brain abnormalities play a role in the onset of schizophrenia:

  • Genetic predisposition: Substantial evidence suggests that there is a genetically inherited predisposition to schizophrenia. For example, there is a concordance rate of about 48 percent for identical twins. The concordance rate for fraternal twins is considerably less, about 17 percent. Concordance rate refers to the percentage of both people in a pair having a certain trait or disorder. A person who has two parents with schizophrenia has about a 46 percent chance of developing schizophrenia. This probability is very high compared to the roughly 1 percent chance of developing schizophrenia in the general population.
  • Neurotransmitters: Some researchers have proposed that schizophrenia is related to an overabundance of the neurotransmitter dopamine in the brain. Other researchers have suggested that both serotonin and dopamine may be implicated. The neurotransmitter glutamate may also play a role in the disorder. Underdevelopment of glutamate neurons results in the overactivity of dopamine neurons.
  • Brain structure: Some researchers have suggested that schizophrenia may involve an inability to filter out irrelevant information, which leads to being overwhelmed by stimuli. With this idea in mind, researchers have looked for brain abnormalities in schizophrenia patients. The brains of people with schizophrenia do differ structurally from the brains of normal people in several ways. For example, they are more likely to have enlarged ventricles, or fluid-filled spaces. They are also more likely to have abnormalities in the thalamus and reduced hippocampus volume.
  • Brain injury: Another line of research suggests that injuries to the brain during sensitive periods of development can make people susceptible to schizophrenia later on in life. For example, researchers believe that viral infections or malnutrition during the prenatal period and complications during the birthing process can increase the later risk of schizophrenia. Some researchers have suggested that abnormal brain development during adolescence may also play a role in schizophrenia.


Many researchers believe stress plays a role in bringing on schizophrenia in people who are already biologically vulnerable to this disorder.

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