Sunday, June 7, 2015

Auditory Hallucination

A paracusia, or auditory hallucination, is a form of hallucination that involves perceiving sounds without auditory stimulus.  Auditory hallucinations need to be distinguished from endaural phenomena in which sounds are heard without any external acoustic stimulation but arise from disorders of the ear or auditory system.

A common form of auditory hallucination involves hearing one or more talking voices. This may be associated with psychotic disorders such as schizophrenia or mania, and holds special significance in diagnosing these conditions.  However, individuals may hear voices without suffering from diagnosable mental illness.

There are three main categories into which the hearing of talking voices can often fall: a person hearing a voice speak one's thoughts, a person hearing one or more voices arguing, or a person hearing a voice narrating his/her own actions.  These three categories do not account for all types of auditory hallucinations.

Other types of auditory hallucination include exploding head syndrome and musical ear syndrome.  In the latter, people will hear music playing in their mind, usually songs they are familiar with. Reports have also mentioned that it is also possible to get musical hallucinations from listening to music for long periods of time.  This can be caused by: lesions on the brain stem (often resulting from a stroke); also, sleep disorders such as narcolepsy, tumors, encephalitis, or abscesses.  Other reasons include hearing loss and epileptic activity.

Potential Causes

Associated diseases

The premier cause of auditory hallucinations in the case of psychotic patients is schizophrenia.  In those cases, patients show a consistent increase in activity of the thalamic and strietal subcortical nuclei, hypothalamus, and paralimbic regions; confirmed via PET scan and fMRI.  Other research shows an enlargement of temporal white matter, frontal gray matter, and temporal gray matter volumes (those areas crucial to both inner and outer speech) when compared to control patients.  This implies both functional and structural abnormalities in the brain can induce auditory hallucinations, both of which may have a genetic component.  Mood disorders have also been known to cause auditory hallucinations, but tend to be milder than their psychosis induced counterpart. Auditory hallucinations are a relatively common sequelae of Major Neurocognitive Disorders (formerly dementia) such as Alzheimer's disease.

Non-disease associated causes

Auditory hallucinations have been known to manifest as a result of intense stress, sleep deprivation, drug use, and errors in development of proper psychological processes.  Genetic correlation has been identified with auditory hallucinations, but most work with non-psychotic causes of auditory hallucinations is still ongoing.

High caffeine consumption has been linked to an increase in the likelihood of experiencing auditory hallucinations. A study conducted by the La Trobe University School of Psychological Sciences revealed that as few as five cups of coffee a day could trigger the phenomenon.

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