Hallucinations and ViolenceThe relationship between hallucinations and violent
behavior has been the subject of debate. Some research
has found a modest positive relationship between hallu-
cinations and violence, whereas other studies found no
immediate relationship. Dale E. McNeil and colleagues
studied the relationship between command hallucina-
tions and violence in a sample of 130 inpatients who
were diagnosed with schizophrenia. They found that
30% of the inpatients reported that they had experi-
enced command hallucinations to hurt someone else in
the past year, while 22% of the patients reported that
they complied with those command hallucinations.
These findings suggest that patients who experienced
command hallucinations were almost twice as likely to
engage in violent behavior as patients who did not
experience command hallucinations. Other studies
have reported compliance for command hallucinations
of violence ranging from 39.2% to 88.5%. Compliance
with command hallucinations has been found to be
related to whether or not the person recognizes the hal-
lucinated voice, with those recognizing the voice being
more likely to obey the command.Hallucinations and Schizophrenia
Hallucinations are most commonly associated with
schizophrenia. Patients with schizophrenia may experi-
ence auditory and/or visual hallucinations. Some
research suggests that auditory hallucinations can be
caused by high levels of the neurotransmitter dopamine
in the patient’s brain. Researchers have found evidence,
however, both to support and to refute the dopamine
hypothesis. The evidence that most strongly supports the
dopamine hypothesis comes from the effects of drugs
such as amphetamines and cocaine. These drugs are
known to increase the levels of dopamine in the brain and
can result in psychotic symptoms, including hallucina-
tions, when large doses are consumed over long periods.
Several studies have found that when patients with schiz-
ophrenia were administered drugs that produce increased
dopamine levels, up to 75% of them had significant
increases in their hallucinations and psychotic symp-
toms, while control subjects without schizophrenia
showed no effects on being administered the same drugs.
Further evidence supporting the dopamine hypothesis
was found following the discovery of a class of drugs
known as phenothiazines, which include antipsychotic
medications. These drugs bind to dopamine receptorsand have been found to decrease the positive symptoms
of schizophrenia, including hallucinations.
With the advent of more sophisticated brain imaging
techniques such as positron emission tomography (PET)
scanning, newer findings challenged the dopamine
hypothesis. In PET studies with schizophrenic patients,
researchers found that in some patients, more than 90%
of the dopamine receptors were blocked by the antipsy-
chotic drugs, yet there was no observed diminution
in psychotic symptoms, including hallucinations.
However, the patients in this study had been receiving
treatment with antipsychotic medications for more than
30 years. In another study, researchers found that 90%
to 95% of patients who were only recently diagnosed
with schizophrenia responded to antipsychotic medica-
tions, and scans of their brains revealed that only 60% to
70% of the dopamine receptors were blocked. Finally, in
recent years, atypical antipsychotic medications have
been developed to treat schizophrenia. While equally as
effective as the typical antipsychotic medications, these
atypical antipsychotic medications block fewer of the
dopamine receptors (about 60–70%). Thus, confronted
by some evidence that supports and other evidence that
refutes the dopamine hypothesis, research continues
into the etiology of schizophrenia.
There has also been a great deal of research investi-
gating the structural and functional abnormalities in the
brains of patients with schizophrenia. Researchers have
found that some people with schizophrenia have changes
in the density of the brain’s gray matter in the frontal
and temporal lobes. If these differences in brain struc-
ture were present since birth, then they could result in
dopamine hypersensitivity as described above, result-
ing in psychotic symptoms such as hallucinations.
Researchers have also noted abnormal patterns in
brain activity among patients with schizophrenia. More
specifically, abnormalities were found in the corollary
discharge mechanism, which enables people to distin-
guish between internal and external stimuli. Studies with
electroencephalograms (EEGs) of the brains of patients
with schizophrenia that were taken while the patients
were talking found that the corollary discharges from the
frontal cortex of the brain (the area where thoughts are
produced) did not provide information to the auditory
cortex (the area in which sounds are interpreted) that
the sounds that were detected were self-generated.
Therefore, this dysfunction would lead patients with
schizophrenia to perceive internal stimuli as being gener-
ated by external sources, thereby producing auditory
hallucinations.346 ———HallucinationsH-Cutler (Encyc)-45463.qxd 11/19/2007 10:49 AM Page 346