An auditory hallucination, or paracusia, is a form of hallucination that involves perceiving sounds without auditory stimulus. While experiencing an auditory hallucination, the affected person hears a sound or sounds that did not come from the natural environment.
A common form of auditory hallucination involves hearing one or more voices without a speaker present, known as an auditory verbal hallucination. This may be associated with psychotic disorders, most notably schizophrenia, and this phenomenon is often used to diagnose these conditions. However, individuals without any mental disorders may hear voices, including those under the influence of mind-altering substances, such as cannabis, cocaine, amphetamines, and PCP due to cannabis-induced psychotic disorder or stimulant psychosis, respectively.
There are three main categories into which the hearing of talking voices 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 their own actions. These three categories do not account for all types of auditory hallucinations.
Hallucinations of music also occur. In these, people more often hear snippets of songs that they know, or the music they hear may be original. They may occur in mentally sound people and with no known cause. Other types of auditory hallucinations 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. These hallucinations can be caused by: lesions on the brain stem (often resulting from a stroke), sleep disorders such as narcolepsy, tumors, encephalitis, or abscesses. This should be distinguished from the commonly experienced phenomenon of earworms, memorable music that persists in one's mind. Reports have also mentioned that it is also possible to get musical hallucinations from listening to music for long periods of time. Other causes include hearing loss and epileptic activity.
In the past, the cause of auditory hallucinations was attributed to cognitive suppression by way of executive function failure of the frontoparietal sulcus. Newer research has found that they coincide with the left superior temporal gyrus, suggesting that they are better attributed to speech misrepresentations. It is assumed through research that the neural pathways involved in normal speech perception and production, which are lateralized to the left temporal lobe, also underlie auditory hallucinations. Auditory hallucinations correspond with spontaneous neural activity of the left temporal lobe, and the subsequent primary auditory cortex. The perception of auditory hallucinations corresponds to the experience of actual external hearing, despite the absence of any sound itself.
Associated with diagnoses
Schizophrenia
In people with psychosis, the premier cause of auditory hallucinations is schizophrenia, and these are known as auditory verbal hallucinations (AVHs). In schizophrenia, people show a consistent increase in activity of the thalamic and striatal subcortical nuclei, hypothalamus, and paralimbic regions; confirmed by PET and fMRI scans. 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 (healthy) control groups. This implies that functional and structural abnormalities in the brain, both of which may have a genetic component, can induce auditory hallucinations.
Auditory verbal hallucinations attributed to an external source, rather than internal, are considered the defining factor for the diagnosis of schizophrenia. The voices heard are generally destructive and emotive, adding to the state of artificial reality and disorientation seen in psychotic patients. The causal basis of hallucinations has been explored on the cellular receptor level. The glutamate hypothesis, proposed as a possible cause for schizophrenia, may also have implications in auditory hallucinations, which are suspected to be triggered by altered glutamatergic transmission.
Studies using dichotic listening methods suggest that people with schizophrenia have major deficits in the functioning of the left temporal lobe by showing that patients do not generally exhibit what is a functionally normal right ear advantage. Inhibitory control of hallucinations in patients has been shown to involve failure of top-down regulation of resting-state networks and up-regulation of effort networks, further impeding normal cognitive functioning.
Not all who experience hallucinations find them to be distressing. The relationship between an individual and their hallucinations is personal, and everyone interacts with their troubles in different ways. People may hear solely malevolent voices, solely benevolent voices, or a mix of the two; some individuals see the hallucinations as either malevolent or benevolent and not believing the voice.
Mood disorders and dementias Auditory hallucinations may also occur in mood disorders (e.g., depression and bipolar disorder), and 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.
Transient causes Auditory hallucinations have been known to manifest as a result of intense stress, sleep deprivation, and drug use. Auditory hallucinations can also occur in mentally healthy individuals during the altered state of consciousness while falling asleep (hypnagogic hallucinations) and waking up (hypnopompic hallucinations).
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. Intoxication of psychoactive drugs such as PCP, amphetamines, cocaine, marijuana and other substances can produce hallucinations in general, especially in high doses. Withdrawal from certain drugs such as alcohol, sedatives, hypnotics, anxiolytics, and opioids can also produce hallucinations, including auditory.
Extreme altitude mountain climbers, especially lone ones, can experience auditory hallucinations due to a combination of hypoxia, social isolation and stress.Brugger P, Regard M, Landis T, Oelz O. Hallucinatory experiences in extreme-altitude climbers. Neuropsychiatry Neuropsychol Behav Neurol. 1999 Jan;12(1):67-71
Pathophysiology The following areas of the brain have been found to be active during auditory hallucinations, through the use of fMRIs.
Transverse temporal gyri (Heschl's gyri): found within the primary auditory cortex. Left temporal lobe: processes semantics in speech and vision, including primary auditory cortex. Broca's area: speech and language comprehension. Superior temporal gyrus: contains primary auditory cortex. Primary auditory cortex: processes hearing and speech perception. Globus pallidus: Regulation of voluntary movement.
Treatments
Medication The primary means of treating auditory hallucinations is antipsychotic medications which affect dopamine metabolism. If the primary diagnosis is a mood disorder (with psychotic features), adjunctive medications are often used (e.g., antidepressants or mood stabilizers). These medical approaches may allow the person to function normally but are not a cure as they do not eradicate the underlying thought disorder.
Therapy Cognitive behavioral therapy has been shown to help decrease the frequency and distressfulness of auditory hallucinations, particularly when other psychotic symptoms were presenting. Enhanced supportive therapy has been shown to reduce the frequency of auditory hallucinations, the violent resistance the patient displayed towards said hallucinations, and an overall decrease in the perceived malignancy of the hallucinations. Other cognitive and behavioural therapies have been used with mixed success.
Another key to therapy is to help patients see that they do not need to obey the voices that they are hearing. It has been seen in patients with schizophrenia and auditory hallucinations that therapy might help confer insight into recognising and choosing to not obey the voices that they hear.
Others Between 25% and 30% of schizophrenia patients do not respond to antipsychotic medication which has led researchers to look for alternate sources to help them. Two common methods to help are electroconvulsive therapy and repetitive transcranial magnetic stimulation (rTMS). Electroconvulsive therapy or ECT has been shown to reduce psychotic symptoms associated with schizophrenia, mania, and depression, and is often used in psychiatric hospitals.
Transcranial magnetic stimulation when used to treat auditory hallucinations in patients with schizophrenia is done at a low frequency of 1 Hertz to the left temporoparietal cortex.
History
Ancient history
Presentation
In the ancient world, auditory hallucinations were often viewed as either a gift or curse by God or the gods (depending on the specific culture). According to the Greek historian Plutarch, during the reign of Tiberius (A.D. 14–37), a sailor named Thamus heard a voice cry out to him from across the water, "Thamus, are you there? When you reach Palodes, take care to proclaim that the great god Pan is dead."Plutarch, Moralia Book 5:17, De defectu oraculorum ("The Obsolescence of Oracles").
The oracles of ancient Greece were known to experience auditory hallucinations while breathing in certain psychoactive vapors (such as the smoke from bay leaves), while the more pervasive delusions and symptomatology were often viewed as possession by demonic forces as punishment for misdeeds.
Treatments
Treatment in the ancient world is ill-documented, but there are some cases of therapeutics being used to attempt treatment, while the common treatment was sacrifice and prayer in an attempt to placate the gods. During the Middle Ages, those with auditory hallucinations were sometimes subjected to trepanning or trial as a witch. In other cases of extreme symptomatology, individuals were seen as being reduced to animals by a curse; these individuals were either left on the streets or imprisoned in insane asylums. It was the latter response that eventually led to modern psychiatric hospitals.
Pre-modern
Presentation
Auditory hallucinations were rethought during the enlightenment. As a result, the predominant theory in the western world beginning in the late 18th century was that auditory hallucinations were the result of a disease in the brain (e.g., mania), and treated as such.
Treatments
There were no effective treatments for hallucinations at this time. Conventional thought was that clean food, water, and air would allow the body to heal itself (sanatorium). Beginning in the 16th century insane asylums were first introduced in order to remove "the mad dogs" from the streets. These asylums acted as prisons until the late 18th century. This is when doctors began the attempt to treat patients. Often attending doctors would douse patients in cold water, starve them, or spin patients on a wheel. Soon, this gave way to brain-specific treatments with the most famous examples including lobotomy, shock therapy, and branding the skull with a hot iron.
Society and culture Notable cases Robert Schumann, a famous music composer, spent the end of his life experiencing auditory hallucinations. One night he claimed to have been visited by the ghost of Schubert and wrote down the music that he was hearing. Thereafter, he began making claims that he could hear an angelic choir singing to him. As his condition worsened, the angelic voices developed into demonic ones.