Musical hallucinations

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Musical hallucinations (also known as auditory hallucinations, auditory Charles Bonnet Syndrome, and Oliver Sacks' syndrome [1] ) describes a neurological disorder in which the patient will hallucinate songs, tunes, instruments and melodies. The source of these hallucinations are derived from underlying psychotic illness or hearing impairment. These hallucinations are often rare and are followed by mental decline. [2] A majority of patients who have symptoms of musical hallucinations are older and have onset conditions predisposing them to the disease. While there is no set form of treatment, research has discovered medications and alternative therapies to be successful in alleviating the hallucinations.

Contents

Description

In 73 individual cases reviewed by Evers and Ellger, 57 patients heard tunes that were familiar, while 5 heard unfamiliar tunes. These tunes ranged from religious pieces to childhood favorites, and also included popular songs from the radio. Vocal and instrumental forms of classical music were also identified in most patients. Keshavan found that the consistent feature of musical hallucinations was that it represented a personal memory trace. Memory traces refer to anything that may seem familiar to the patient, which indicate why certain childhood or familiar songs were heard. [3] [4]

For the case of an 84 year old widow who complained of hearing sounds, she described her symptoms as pleasant, but also sought for treatment because she felt distracted. The music that played over her head was similar to the hymns and songs sung at her own wedding. Moreover, she had been widowed for a while and had no signs of psychiatric disorders. However, she did have hypertension, hyperthyroidism, and osteoporosis. From these diagnosis it was theorized that the distress from the illnesses manifested the hallucinations. Through further analysis, researchers found that due the unexpected origin of the hallucinations, there is no clear diagnosis or treatments to carry out.

Another case, which studies a 74-year-old woman, described her symptoms as music that would play in short verses of patriotic and children's songs. [5] These symptoms would occur when the patient was alone and much more frequently when driving. Researchers suspected her hearing loss as a factor for developing the hallucinations. Moreover, through further analysis the patient had a medical history of hypertension, hyperlipidemia, and atrial fibrillations.

Oftentimes, cases are commonly found in the elderly, but a 29-year-old female reported hearing music for one week. Prior to her hallucinations, the patient had undergone surgery for intraventricular and intracranial hemorrhages. Following her recovery, she mentioned the onset of hallucinations followed by headaches. [6] Through scans, doctors found no neurological impairments, but prescribed her with medication. For her, the symptoms only lasted a year due to the treatment of quetiapine, which she responded well to.

Causes

Musical hallucinations can occur in people who are physically and mentally healthy, and for them, there is no known cause. [7] Most people find their musical hallucinations obtrusive, and wish to be rid of them, while others welcome them. In addition, investigators have pointed to factors that are associated with musical hallucinations. Evers and Ellgers compiled a significant portion of musical hallucination articles, case studies etc. and were able to categorize five major etiologies:

Hypoacusis

Hypoacusis is defined as impairment in hearing or deafness. Hypoacusis is one of five etiologies of musical hallucinations, and is the most common in the case studies reviewed by Evers and Ellgers. [3] According to Sanchez et al. 2011, there have been suggestions that pontine lesions could alter the central auditory system's function causing hypoacusis and musical hallucinations. [8] [9]

Psychiatric disorders

A case study by Janakiraman et al. 2006, revealed a 93‑year‑old woman with major depressive disorder who experienced musical hallucinations while treated with electroconvulsive therapy (ECT). Investigators found that the patient's depression symptoms were inversely related to her hallucinations and primarily stemmed from the ECT treatment. The patient had no known abnormalities in hearing, suggesting that musical hallucinations could arise from a variety of sources including psychiatric illnesses. After a complete course of ECT, her hallucinations dissipated, also suggesting that they can be acute. [10]

According to Evers and Ellgers, some other major psychiatric disorders that contribute to musical hallucinations include schizophrenia and depression. Some patients who have schizophrenia experience musical hallucinations due to their ongoing psychosis, but there are some cases that do so without psychosis. There are also a very small percentage of musical hallucination cases due to obsessive-compulsive disorder (OCD). [3]

Several different types of psychiatric disorders can be precursors for Musical Hallucinations. according to Blom and Coebergh, Bipolar Disorder and personality disorders can increase the chances of musical hallucinations. Likewise, cocaine dependence can elevate the symptoms.

Focal brain lesions

Among the handful of cases that Evers and Ellgers studied, major lesion sites included the temporal cortex; however, the specific location and laterality (left vs. right temporal cortex) was variable. Many cases of focal brain lesions had comorbidity with hearing impairment (see hypoacusis), epileptic activity and intoxication. [3] There have also been several findings of acute musical hallucinations in patients with dorsal pons lesions post-stroke and encephalitis potentially due to disruption of connections between the sensory cortex and reticular formation. [11] Also, any kind of traumatic lesion imposed on the brain can be a risk factor for Musical Hallucinations.

Epilepsy

Epileptic brain activity in musical hallucinations originates in the left or right temporal lobe. [3] In a specific case studied by Williams et al. 2008, a patient who received a left temporal lobectomy in order to treat epilepsy was diagnosed with musical hallucinations post-surgery. The patient also had multiple additional risk factors that could have accounted for the hallucinations including mild neuropsychiatric dysfunction and tinnitus. [12] The causation of hallucination through epilepsy is linked to seizure episodes. Through experiments, researchers have found that patients with epilepsy and hallucinations will respond to antiepileptics and surgery [13]

Intoxication

Intoxication accounts for a small percentage of musical hallucination cases. Intoxication leads to either withdrawal or inflammatory encephalopathy, which are major contributors to musical hallucinations. Some of the drugs that have been found to relate to musical hallucinations include salicylates, benzodiazepines, pentoxifylline, propranolol, clomipramine, amphetamine, quinine, imipramine, a phenothiazine, carbamazepine, marijuana, paracetamol, phenytoin, procaine, and alcohol. General anesthesia has also been associated with musical hallucinations. [3] In a case study by Gondim et al. 2010, a seventy–seven-year-old woman with Parkinson's disease (PD) was administered amantadine after a year of various other antiparkinsonian treatments. Two days into her treatment, she started to experience musical hallucinations, which consisted of four musical pieces. The music persisted until three days after cessation of the drug. Although the patient was taking other medications at the same time, the timing of onset and offset suggested that amantadine either had a synergistic effect with the other drugs or simply caused the hallucinations. Although the case wasn't specific to intoxication, it leads to the idea that persons with PD who are treated with certain drugs can experience musical hallucinations. [14]

Other risk factors

In summary, musical hallucinations can be separated into five categories according to their cause: hypoacusis, psychiatric disorders, brain lesions, epilepsy, and substance use. However, certain factors can trigger hallucinations, these factors include, old age, social isolation and even gender. [15] Many cases highlight female patients who have the disease. Overall, psychiatric disorders and neurological disease lead to hallucinations, but certain factors, such as age and gender play a role in heightening the causation.

Imaging

Positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) show that musical hallucinations activate a wide variety of areas in the brain including the following: auditory areas, motor cortex, visual areas, basal ganglia, brainstem, pons, tegmentum, cerebellum, hippocampi, amygdala, and peripheral auditory system. [16]

Treatment

To date, there is no successful method of treatment that "cures" musical hallucinations. There have been successful therapies in single cases that have ameliorated the hallucinations. Some of these successes include drugs such as neuroleptics, antidepressants, and certain anticonvulsive drugs. A musical hallucination was alleviated, for example, by antidepressant medications given to patients with depression. [3] Sanchez reported that some authors have suggested that the use of hearing aids may improve musical hallucination symptoms. [9] They believed that the external environment influences the auditory hallucinations, showing worsening of symptoms in quieter environments than in noisier ones. [8] [17] [18] Oliver Sacks' patient, Mrs. O'C, reported being in an "ocean of sound" despite being in a quiet room due to a small thrombosis or infarction in her right temporal lobe. After treatment, Mrs. O'C was relinquished of her musical experience but said that, "I do miss the old songs. Now, with lots of them, I can't even recall them. It was like being given back a forgotten bit of my childhood again." Sacks also reported another elderly woman, Mrs. O'M, who had a mild case of deafness and reported hearing musical pieces. When she was treated with anticonvulsive medications, her musical hallucinations ceased but when asked if she missed them, she said "Not on your life." [19]

Researchers found that patients with musical hallucinations respond well to the drug Donepezil, making it another potential treatment for the condition. Donepezil, which belongs to a class of medication called acetylcholinesterase inhibitors, is most commonly used to treat dementia in patients with Alzheimer's disease. Although it cannot cure Alzheimer's, it can provide patients with a better quality of life by inhibiting the loss of function and improving the ability to think. [20] For patients with musical hallucinations, the medication keeps them more aware and stimulated to control the onset symptoms of hallucinations. Overall, with few adverse effects, research has found that donepezil is an effective and safe choice of treatment. [21]

History

According to Oliver Sacks' Hallucinations , the first known medical report of musical hallucinations was published in 1846, by French alienist Jules Baillarger. [16] However, the first scientific description of the disorder was reported in the early 1900s. In the last three decades, Berrios has reported case studies in 1990 and 1991 along with Keshavan et al. in 1992. Berrios concluded that confirmed diagnoses of deafness, ear disease, brain disease, advanced age and drug use are all important factors in the development of musical hallucinations. After analyzing 46 cases, Berrios found a female predominance of 80% in women over the age of 60. The study concluded that musical hallucinations were more likely to be seen in elderly women affected by deafness or brain disease than in individuals with no psychiatric illness at all. [22] [4]

Keshevan and Berrios were the first authors to identify classes of musical hallucinations. These classes consisted of hearing loss, coarse brain disease (i.e. tumors), epileptic disorder, stroke, and psychiatric disorder. Although no statistical analyses were performed, the authors stated that deafness was the most strongly related factor in musical hallucinations and that there was a female predominance, which could entail a genetic component. [3] [22] [4]

Related Research Articles

Psychosis is a condition of the mind that results in difficulties determining what is real and what is not real. Symptoms may include delusions and hallucinations, among other features. Additional symptoms are incoherent speech and behavior that is inappropriate for a given situation. There may also be sleep problems, social withdrawal, lack of motivation, and difficulties carrying out daily activities. Psychosis can have serious adverse outcomes.

<span class="mw-page-title-main">Hallucination</span> Perception in the absence of external stimulation that has the qualities of real perception

A hallucination is a perception in the absence of an external stimulus that has the qualities of a real perception. Hallucinations are vivid, substantial, and are perceived to be located in external objective space. Hallucination is a combination of two conscious states of brain wakefulness and REM sleep. They are distinguishable from several related phenomena, such as dreaming, which does not involve wakefulness; pseudohallucination, which does not mimic real perception, and is accurately perceived as unreal; illusion, which involves distorted or misinterpreted real perception; and mental imagery, which does not mimic real perception, and is under voluntary control. Hallucinations also differ from "delusional perceptions", in which a correctly sensed and interpreted stimulus is given some additional significance. Many hallucinations happen also during sleep paralysis.

Schizoaffective disorder is a mental disorder characterized by abnormal thought processes and an unstable mood. This diagnosis requires symptoms of both schizophrenia and a mood disorder: either bipolar disorder or depression. The main criterion is the presence of psychotic symptoms for at least two weeks without any mood symptoms. Schizoaffective disorder can often be misdiagnosed when the correct diagnosis may be psychotic depression, bipolar I disorder, schizophreniform disorder, or schizophrenia. This is a problem as treatment and prognosis differ greatly for most of these diagnoses.

The Fregoli delusion is a rare disorder in which a person holds a delusional belief that different people are in fact a single person who changes appearance or is in disguise. The syndrome may be related to a brain lesion and is often of a paranoid nature, with the delusional person believing themselves persecuted by the person they believe is in disguise.

Encephalopathy means any disorder or disease of the brain, especially chronic degenerative conditions. In modern usage, encephalopathy does not refer to a single disease, but rather to a syndrome of overall brain dysfunction; this syndrome has many possible organic and inorganic causes.

The mental status examination (MSE) is an important part of the clinical assessment process in neurological and psychiatric practice. It is a structured way of observing and describing a patient's psychological functioning at a given point in time, under the domains of appearance, attitude, behavior, mood and affect, speech, thought process, thought content, perception, cognition, insight, and judgment. There are some minor variations in the subdivision of the MSE and the sequence and names of MSE domains.

The syndrome of subjective doubles is a rare delusional misidentification syndrome in which a person experiences the delusion that they have a double or Doppelgänger with the same appearance, but usually with different character traits, that is leading a life of its own. The syndrome is also called the syndrome of doubles of the self, delusion of subjective doubles, or simply subjective doubles. Sometimes, the patient is under the impression that there is more than one double. A double may be projected onto any person, from a stranger to a family member.

Neuropsychiatry is a branch of medicine that deals with psychiatry as it relates to neurology, in an effort to understand and attribute behavior to the interaction of neurobiology and social psychology factors. Within neuropsychiatry, the mind is considered "as an emergent property of the brain", whereas other behavioral and neurological specialties might consider the two as separate entities. Those disciplines are typically practiced separately.

<span class="mw-page-title-main">Emergency psychiatry</span> Clinical application of psychiatry in emergency settings

Emergency psychiatry is the clinical application of psychiatry in emergency settings. Conditions requiring psychiatric interventions may include attempted suicide, substance abuse, depression, psychosis, violence or other rapid changes in behavior.

<span class="mw-page-title-main">Arachnoid cyst</span> Medical condition

Arachnoid cysts are cerebrospinal fluid covered by arachnoidal cells and collagen that may develop between the surface of the brain and the cranial base or on the arachnoid membrane, one of the three meningeal layers that cover the brain and the spinal cord. Primary arachnoid cysts are a congenital disorder whereas secondary arachnoid cysts are the result of head injury or trauma. Most cases of primary cysts begin during infancy; however, onset may be delayed until adolescence.

Auditory verbal agnosia (AVA), also known as pure word deafness, is the inability to comprehend speech. Individuals with this disorder lose the ability to understand language, repeat words, and write from dictation. Some patients with AVA describe hearing spoken language as meaningless noise, often as though the person speaking was doing so in a foreign language. However, spontaneous speaking, reading, and writing are preserved. The maintenance of the ability to process non-speech auditory information, including music, also remains relatively more intact than spoken language comprehension. Individuals who exhibit pure word deafness are also still able to recognize non-verbal sounds. The ability to interpret language via lip reading, hand gestures, and context clues is preserved as well. Sometimes, this agnosia is preceded by cortical deafness; however, this is not always the case. Researchers have documented that in most patients exhibiting auditory verbal agnosia, the discrimination of consonants is more difficult than that of vowels, but as with most neurological disorders, there is variation among patients.

Phantosmia, also called an olfactory hallucination or a phantom odor, is smelling an odor that is not actually there. This is intrinsically suspicious as the formal evaluation and detection of relatively low levels of odour particles is itself a very tricky task in air epistemology. It can occur in one nostril or both. Unpleasant phantosmia, cacosmia, is more common and is often described as smelling something that is burned, foul, spoiled, or rotten. Experiencing occasional phantom smells is normal and usually goes away on its own in time. When hallucinations of this type do not seem to go away or when they keep coming back, it can be very upsetting and can disrupt an individual's quality of life.

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.

<span class="mw-page-title-main">Cortical deafness</span> Medical condition

Cortical deafness is a rare form of sensorineural hearing loss caused by damage to the primary auditory cortex. Cortical deafness is an auditory disorder where the patient is unable to hear sounds but has no apparent damage to the structures of the ear. It has been argued to be as the combination of auditory verbal agnosia and auditory agnosia. Patients with cortical deafness cannot hear any sounds, that is, they are not aware of sounds including non-speech, voices, and speech sounds. Although patients appear and feel completely deaf, they can still exhibit some reflex responses such as turning their head towards a loud sound.

Musical ear syndrome (MES) describes a condition seen in people who have hearing loss and subsequently develop auditory hallucinations. "MES" has also been associated with musical hallucinations, which is a complex form of auditory hallucinations where an individual may experience music or sounds that are heard without an external source. It is comparable to Charles Bonnet syndrome and some have suggested this phenomenon could be included under this diagnosis.

Auditory agnosia is a form of agnosia that manifests itself primarily in the inability to recognize or differentiate between sounds. It is not a defect of the ear or "hearing", but rather a neurological inability of the brain to process sound meaning. While auditory agnosia impairs the understanding of sounds, other abilities such as reading, writing, and speaking are not hindered. It is caused by bilateral damage to the anterior superior temporal gyrus, which is part of the auditory pathway responsible for sound recognition, the auditory "what" pathway.

Neuroscientists have learned much about the role of the brain in numerous cognitive mechanisms by understanding corresponding disorders. Similarly, neuroscientists have come to learn much about music cognition by studying music-specific disorders. Even though music is most often viewed from a "historical perspective rather than a biological one" music has significantly gained the attention of neuroscientists all around the world. For many centuries music has been strongly associated with art and culture. The reason for this increased interest in music is because it "provides a tool to study numerous aspects of neuroscience, from motor skill learning to emotion".

Schizophrenia is a primary psychotic disorder, whereas, bipolar disorder is a primary mood disorder which can also involve psychosis. Both schizophrenia and bipolar disorder are characterized as critical psychiatric disorders in the Diagnostic and Statistical Manual of Mental Disorders fifth edition (DSM-5). However, because of some similar symptoms, differentiating between the two can sometimes be difficult; indeed, there is an intermediate diagnosis termed schizoaffective disorder.

<span class="mw-page-title-main">Tactile hallucination</span>

Tactile hallucination is the false perception of tactile sensory input that creates a hallucinatory sensation of physical contact with an imaginary object. It is caused by the faulty integration of the tactile sensory neural signals generated in the spinal cord and the thalamus and sent to the primary somatosensory cortex (SI) and secondary somatosensory cortex (SII). Tactile hallucinations are recurrent symptoms of neurological diseases such as schizophrenia, Parkinson's disease, Ekbom's syndrome and delirium tremens. Patients who experience phantom limb pains also experience a type of tactile hallucination. Tactile hallucinations are also caused by drugs such as cocaine and alcohol.

Musicogenic seizure, also known as music-induced seizure, is a rare type of seizure, with an estimated prevalence of 1 in 10,000,000 individuals, that arises from disorganized or abnormal brain electrical activity when a person hears or is exposed to a specific type of sound or musical stimuli. There are challenges when diagnosing a music-induced seizure due to the broad scope of triggers, and time delay between a stimulus and seizure. In addition, the causes of musicogenic seizures are not well-established as solely limited cases and research have been discovered and conducted respectively. Nevertheless, the current understanding of the mechanism behind musicogenic seizure is that music triggers the part of the brain that is responsible for evoking an emotion associated with that music. Dysfunction in this system leads to an abnormal release of dopamine, eventually inducing seizure.

References

  1. ↑ Blom, Jan Dirk; Coebergh, Jan Adriaan F.; Lauw, René; Sommer, Iris E. C. (2015). "Musical Hallucinations Treated with Acetylcholinesterase Inhibitors". Frontiers in Psychiatry. 6: 46. doi: 10.3389/fpsyt.2015.00046 . ISSN   1664-0640. PMC   4387860 . PMID   25904872.
  2. ↑ Golden, Erin C.; Josephs, Keith A. (December 2015). "Minds on replay: musical hallucinations and their relationship to neurological disease". Brain: A Journal of Neurology. 138 (Pt 12): 3793–3802. doi: 10.1093/brain/awv286 . ISSN   1460-2156. PMID   26446167.
  3. 1 2 3 4 5 6 7 8 Evers, S; Ellger, T (2004). "The clinical spectrum of musical hallucinations". Journal of the Neurological Sciences. 227 (1): 55–65. doi:10.1016/j.jns.2004.08.004. PMID   15546592. S2CID   23786425.
  4. 1 2 3 Keshavan, M.S.; David, A.S.; Steingard, S.; Lishman, W.A. (1992). "Musical hallucinations: a review and synthesis". Cognitive and Behavioral Neurology. 3 (3): 211–23.
  5. ↑ Brunner, Jacob P.; Amedee, Ronald G. (2015). "Musical Hallucinations in a Patient with Presbycusis: A Case Report". The Ochsner Journal. 15 (1): 89–91. ISSN   1524-5012. PMC   4365855 . PMID   25829887.
  6. ↑ Doluweera, Yasira; Suraweera, Chathurie (2018-06-27). "Those Who Hear Music: Three Cases on Musical Hallucinations". Case Reports in Psychiatry. 2018: 1–3. doi: 10.1155/2018/9361382 . PMC   6040295 . PMID   30050719.
  7. ↑ Deutsch, D. (2019). "Hallucinations of music and speech". Musical Illusions and Phantom Words: How Music and Speech Unlock Mysteries of the Brain. Oxford University Press. ISBN   9780190206833. LCCN   2018051786.
  8. 1 2 Hammeke, TA; McQuillen, MP; Cohen, BA (1983). "Musical hallucinations associated with acquired deafness". Journal of Neurology, Neurosurgery, and Psychiatry. 46 (6): 570–2. doi:10.1136/jnnp.46.6.570. PMC   1027453 . PMID   6875592.
  9. 1 2 Sanchez, TG; Rocha, SC; Knobel, KA; Kii, MA; Santos, RM; Pereira, CB (2011). "Musical hallucination associated with hearing loss". Arquivos de Neuro-Psiquiatria. 69 (2B): 395–400. doi: 10.1590/s0004-282x2011000300024 . PMID   21625772.
  10. ↑ Janakiraman, R; Wildgoose, K; Seelam, K (2006). "ECT associated musical hallucinations in an elderly patient: a case report". Annals of General Psychiatry. 5: 10. doi: 10.1186/1744-859X-5-10 . PMC   1557851 . PMID   16889667.
  11. ↑ Schielke, E; Reuter, U; Hoffmann, O; Weber, JR (2000). "Musical hallucinations with dorsal pontine lesions". Neurology. 55 (3): 454–5. doi:10.1212/wnl.55.3.454. PMID   10932294. S2CID   35439732.
  12. ↑ Williams, VG; Tremont, G; Blum, AS (2008). "Musical hallucinations after left temporal lobectomy". Cognitive and Behavioral Neurology. 21 (1): 38–40. doi:10.1097/WNN.0b013e318165a9e1. PMID   18327022. S2CID   6121424.
  13. ↑ Coebergh, Jan A. F.; Lauw, R. F.; Bots, R.; Sommer, I. E. C.; Blom, J. D. (2015-06-16). "Musical hallucinations: review of treatment effects". Frontiers in Psychology. 6: 814. doi: 10.3389/fpsyg.2015.00814 . ISSN   1664-1078. PMC   4468361 . PMID   26136708.
  14. ↑ Gondim, Francisco de Assis Aquino; Costa, Helida A.; Taunay, Tauily C.D.; de Oliveira, Gisele R.; Ferreira, Jamile Magalhães; Rola, Francisco H. (2010). "Transient amantadine‑induced musical hallucinations in a patient with Parkinson's disease". Movement Disorders. Wiley-Blackwell. 25 (10): 1505–1506. doi:10.1002/mds.22553. ISSN   0885-3185. PMID   20629118. S2CID   6506795.
  15. ↑ Alvarez Perez, Purificacion; Garcia-Antelo, Maria Jose; Rubio-Nazabal, Eduardo (2017-02-28). ""Doctor, I Hear Music": A Brief Review About Musical Hallucinations". The Open Neurology Journal. 11: 11–14. doi: 10.2174/1874205X01711010011 . ISSN   1874-205X. PMC   5420178 . PMID   28567134.
  16. 1 2 Sacks, Oliver (2012). Hallucinations (1st American ed.). New York: Alfred A. Knopf. ISBN   978-0-307-95724-5.
  17. ↑ Miller, TC; Crosby, TW (Mar 1979). "Musical hallucinations in a deaf elderly patient". Annals of Neurology. 5 (3): 301–2. doi:10.1002/ana.410050314. PMID   443762. S2CID   11598486.
  18. ↑ Ross, Elliott D. (1975-02-10). "Musical Hallucinations in Deafness". Journal of the American Medical Association. 231 (6): 620–2. doi:10.1001/jama.1975.03240180056018. PMID   1172847.
  19. ↑ Sacks, Oliver (1998). The man who mistook his wife for a hat and other clinical tales (1st Touchstone ed.). New York, NY: Simon & Schuster. ISBN   978-0-684-85394-9.
  20. ↑ "Donepezil: MedlinePlus Drug Information". medlineplus.gov. Retrieved 2020-12-11.
  21. ↑ Ukai, Satoshi; Yamamoto, Masakiyo; Tanaka, Michio; Shinosaki, Kazuhiro; Takeda, Masatoshi (2007). "Donepezil in the treatment of musical hallucinations". Psychiatry and Clinical Neurosciences. 61 (2): 190–192. doi:10.1111/j.1440-1819.2007.01636.x. ISSN   1440-1819. PMID   17362438. S2CID   39830178.
  22. 1 2 Berrios, GE (1990). "Musical hallucinations. A historical and clinical study". British Journal of Psychiatry. 156 (2): 188–94. doi:10.1192/bjp.156.2.188. PMID   2180526. S2CID   3210326.
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