With normal hearing, sound waves start a series of vibrations that send signals to the brain, according to Macalester College. But, with auditory hallucinations, there are no incoming auditory stimuli to cause the sounds. Auditory hallucinations range from individual sounds, like a hand clap, to more complex ones, like speech. The National Institutes of Health (NIH) states that auditory hallucinations are caused by disorders of the brain, like schizophrenia and post-traumatic stress disorder (PTSD), or drug abuse.
Schizophrenia
A psychiatric disorder that affects about 1 percent of adults in the United States, schizophrenia has symptoms of psychosis, states the National Institute of Mental Health (NIMH). The most common type of hallucinations in schizophrenic patients is auditory, where patients hear voices. These imaginary voices "talk" to the patient about her behavior, may give her orders or warn her about impending dangers. These types of hallucinations can also been seen in other disorders with psychotic symptoms, like certain forms of depression and bipolar disorder.
Auditory hallucinations in schizophrenia are caused by changes in normal brain activity. When a schizophrenic patient's brain is scanned with a PET scan or fMRI, the paralimbic regions, subcortical nuclei and limbic structures are activated, which are brain regions associated with auditory hallucinations, according to "A Functional Neuroanatomy of Hallucinations in Schizophrenia" by DA Silberweig et al. Research by Christian Gaser et al in "Neuroanatomy of 'Hearing Voices': A Frontotemporal Brain Structural Abnormality Associated with Auditory Hallucinations in Schizophrenia" adds that schizophrenic patients have a decrease in brain volume in the primary auditory cortex, inferior supramarginal gyrus and inferior right prefrontal gyri.
PTSD
While not common, the University of Pennsylvania Behavioral Health Department explains that some PTSD patients experience auditory hallucinations. A PTSD patient with auditory hallucinations can hear either voices, like schizophrenic patients, or ringing in his ears. PTSD is a type of anxiety that stems from a traumatic experience. In severe cases, the patient's brain structure can be altered by the excess release of certain stress hormones, like cortisol, which results in the auditory hallucinations.
Hallucinogens
A group of illicit drugs, hallucinogens can mimic psychosis, similar to what is experienced by schizophrenic patients. New England College states that LSD, or lysergic acid diethylamide, produces severe auditory hallucinations by altering chemicals in the brain, which temporarily impacts normal brain function. LSD can also result in visual hallucinations, as well as flashbacks and disorientation.
References
- Macalester College: What are Auditory Hallucinations?
- NIMH: Schizophrenia
- University of Pennsylvania Behavioral Health Department: Post-Traumatic Stress Disorder
- New England College: Wellness Information
- Cerebral Cortex: "Neuroanatomy of 'Hearing Voices': A Frontotemporal Brain Structural Abnormality Associated with Auditory Hallucinations in Schizophrenia"; Christian Gaser et al; January 2004
