Amusia is an innate or acquired inability to perceive and reproduce musical rhythms, melodies. Patients with amusia lose the ability to master musical notation, cannot perform vocal parts and instrumental compositions, do not recognize familiar melodies. Oral speech is preserved at the same time. Diagnostic examination includes neuroimaging studies (brain CT or MRI), assessment of musical abilities. Treatment of the underlying neurological disorder and music therapy lead to improvement of impaired functions.
Amusia, or musical agnosia, is a violation of one or more basic processes of processing musical signals. Deficient perception of music can be acquired or innate. Congenital amusia is also known as “tone deafness”, it affects about 5% of the world’s population. The prevalence of acquired cases is unknown, but more often a disorder of musical abilities is diagnosed in women over 50 years of age. The majority of them are right-handed, left-handed and ambidextrous occur in isolated cases.
Congenital musical agnosia, presumably, is genetically determined – this is indicated by studies demonstrating that close relatives often have similar violations of the processing of musical information. Most likely, this disorder is associated with structural changes in the frontal and temporal lobes of the predominantly right hemisphere of the brain.
Acquired amusia occurs as a result of pathological processes developing in the right auditory cortex or simultaneously in both hemispheres:
- brain infarction;
- hemorrhagic stroke;
- traumatic brain injury;
- brain tumors;
- neurodegenerative diseases;
- arteriovenous malformation;
- neurosurgical operations.
Known cases of amusia differ in the causes, mechanisms of development and anatomical localization of the lesion. It is believed that the right primary (Brodman field 41) and the secondary auditory cortex (field 42) are crucial for the perception of music. Comparative studies of right-handed people with ischemic stroke in the area of the right and left middle cerebral artery show that patients with damage to the right hemisphere develop more severe amusia than those with damage to the left brain.
The right hemisphere is responsible for reproducing the melodic contour in general terms, while the left hemisphere performs analytical processing tasks, encodes each note and interval in this melodic contour. The musical rhythm is processed in several areas, and a violation of its processing is found in patients with right-sided or left-sided cerebral injuries. The right hemisphere is involved in the process of learning and memorizing unfamiliar melodies, and the recognition of familiar melodies depends more on the left hemisphere.
According to MRI data, people with congenital amusia have less white matter than healthy individuals, especially in the area of the right inferior frontal gyrus. This probably leads to a weakening of the frontotemporal connections and a deterioration in the ability to process musical sounds.
Attempts to classify amusia cause controversy regarding the criteria for its division, since the violation of musical abilities is considered quite rare and little studied phenomenon. Thus, the American neuropsychologist A.L. Benton identified more than 10 types of amusia, including receptive and expressive. Modern clinical classification distinguishes the following variants of amusia:
- motor – loss of the ability to sing, hum or whistle a melody;
- sensory (musical deafness) – loss of the ability to distinguish notes;
- instrumental (musical apraxia) – loss of the ability to play a musical instrument;
- musical amnesia is the inability to recognize well – known pieces of music;
- musical agraphy ‒ inability to write music;
- musical alexia is the inability to read notes.
Patients with congenital musical agnosia have difficulty understanding music, although their physical and phonemic hearing, as well as other cognitive functions, remain, as a rule, unaffected. Concomitant neurological disorders (hearing, vision, dizziness, memory loss) are usually characteristic of acquired amusia. In some cases, aphasia, alexia, agraphy, dysprosody may occur.
The spectrum of disorders accompanying amusia is different: patients may lose the ability to sing, recognize melodies, play musical instruments, read sheet music, write music. At the same time, in some cases perception may be disrupted, in others ‒ performance, in the third ‒ musical memory, and in the fourth – the whole complex of processes of processing musical material.
Sometimes patients stop experiencing aesthetic pleasure from listening to their favorite tunes. Emotional connection with music is lost, patients cannot understand the meaning of the melody, characterize it (tempo, mood, etc.), name the sounding instruments. Music can even become unpleasant – it is compared to the grinding of metal, annoying noise. Patients stop attending concerts and listening to music at home.
Amusia can affect not only professional musicians and passionate music lovers, but even those who do not have musical education and special knowledge. However, since the latter group of patients often does not realize the musical deficit and does not report it, these cases of amusia are not taken into account in the general statistics.
Amusia does not lead to somatic complications. Rather, it can cause psychological discomfort and a decrease in the quality of life of musically gifted people. If the disorder occurs in a professional musician, then the possibility of continuing a musical career is called into question. The consequences of the underlying disease are dangerous to health: stroke, head injury, growing tumor, progressive neurodegenerative process, etc. In the countries of Southeast Asia, where tonal languages are used (tone expresses lexical and grammatical differences), amusia leads to difficulties in understanding speech and active utterance.
Patients with amusia need neurological and neuropsychological examination. The first group of diagnostic methods is aimed at verifying the causes of the disorder, the second – at determining the presence and type of musical agnosia.
- Neuroimaging methods. In order to detect the lesion (nature, localization, prevalence), CT or MRI scanning of brain structures is performed. Recording of the activity of auditory processing of music is carried out using magnetoencephalography. fMRI and PET-CT are used for scientific purposes.
- Neuropsychological tests. The Montreal Amusia Assessment Battery (MBEA) is used for standardized assessment of musical abilities. It consists of 6 tests to assess the perception of melody, musical intervals, scales, rhythm, meter and memory. Other types of memory, attention, and visual-spatial functions are also being investigated.
Treatment of musical disorders includes therapy of the underlying disease, neuropsychological correction, melodic-intonation therapy. Patients who have suffered a stroke are prescribed pharmacotherapy, physical rehabilitation (mechanotherapy, physical therapy), logotherapy. Surgical interventions are performed in patients with a neurosurgical profile: removal of intracranial hematomas, embolization of brain AVMs, removal of cerebral tumors. Patients with cerebral degenerations, along with drug therapy, are shown psychotherapy, neuropsychological correction.
Generally accepted methods of correction of amusia have not been proposed for today. The development of rehabilitation programs is experimental. They are based on the use of rhythmic exercises, music therapy, vocalotherapy, training of auditory attention. It is possible to improve musical abilities with congenital amusia through systematic purposeful music education.
Prognosis and prevention
Both primary and secondary amusia occur more often than is diagnosed in clinical neurology. Congenital forms of musical hearing impairment are better amenable to correction than acquired ones. Some patients are forced to permanently abandon music classes, professions, attending concerts, because they lose their skills, and music causes them negative emotions.
Prevention of amusia is associated with a reduction in risk factors for stroke, head injuries, cerebral tumors, dementia. It is necessary to monitor nutrition, blood pressure, maintain mental and physical activity.