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 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 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:
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
type: Characterized by disorganized behavior, disorganized
speech, and emotional flatness or inappropriateness.
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.
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.
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
Many researchers believe stress plays a role in bringing on
schizophrenia in people who are already biologically vulnerable to this