[8] Clinical, or expressive, symptoms include the loss of ability to sing, write musical notation, and/or play an instrument.
Additionally, brain damage to the receptive dimension affects the faculty to discriminate tunes (receptive or sensorial amusia), the ability to read music (musical alessia), and the ability to identify songs that were familiar prior to the brain damage (amnesic amusia).
Those with congenital amusia show impaired performance on discrimination, identification and imitation of sentences with intonational differences in pitch direction in their final word.
[15] Research has been shown that amusia may be related to an increase in size of the cerebral cortex, which may be a result of a malformation in cortical development.
[19] This protocol has at its center the Montreal Battery of Evaluation of Amusia (MBEA),[20] which involves a series of tests that evaluate the use of musical characteristics known to contribute to the memory and perception of conventional music,[21] but the protocol also allows for the ruling out of other conditions that can explain the clinical signs observed.
[2] An individual is considered amusic if they perform two standard deviations below the mean obtained by musically competent controls.
[citation needed] This musical pitch disorder represents a phenotype that serves to identify the associated neuro-genetic factors.
[citation needed] Congenital amusia, commonly known as tone deafness or a tin ear,[7] refers to a musical disability that cannot be explained by prior brain lesion, hearing loss, cognitive defects, or lack of environmental stimulation,[21] and it affects about 4% of the population.
[23] They are unable to recognize or hum familiar tunes even if they have normal audiometry and above-average intellectual and memory skills.
Also, they do not show sensitivity to dissonant chords in a melodic context, which, as discussed earlier, is one of the musical predispositions exhibited by infants.
[citation needed] This could be evidence that the ability to reproduce and distinguish between notes may be a learned skill; conversely, it may suggest that the genetic predisposition towards accurate pitch discrimination may influence the linguistic development of a population towards tonality.
[17] A study was published in 2009 which investigated the neural and cognitive mechanisms that underlie acquired amusia and contribute to its recovery.
Amusia is a common occurrence following an ischemic MCA stroke, as evidenced by the 60% of patients who were found to be amusic at the one-week post-stroke stage.
[2] The opposite scenario can also occur, in which the individual loses pitch discrimination capabilities, but can sense and appreciate the tonal context of the work.
A patient can undergo brain damage that renders them unable to recognize familiar melodies that are presented without words.
However, the patient maintains the ability to recognize spoken lyrics or words, familiar voices, and environmental sounds.
[2] Many research studies of individuals with amusia show that a number of cortical regions appear to be involved in processing music.
Some report that the primary auditory cortex, secondary auditory cortex, and limbic system are responsible for this faculty, while more recent studies suggest that lesions in other cortical areas, abnormalities in cortical thickness, and deficiency in neural connectivity and brain plasticity may contribute to amusia.
While various causes of amusia exist, some general findings that provide insight to the brain mechanisms involved in music processing are discussed below.
[29] In addition, the right anterolateral part of Heschl's gyrus (primary auditory cortex) is also concerned with processing pitch information.
[33] Therefore, a lack of involvement and networking between bilateral temporal cortices and neural motor centers may contribute to both congenital and acquired amusia.
Studies suggest that there is a rich interconnection between the right temporal gyrus and frontal cortical areas for working memory in music appreciation.
[39] In 1865, Jean-Baptiste Bouillaud described the first series of cases that involved the loss of music abilities that were due to brain injury.
[40][41] Later, during the late nineteenth century, several influential neurologists studied language in an attempt to construct a theory of cognition.
[42] While the possibility that certain individuals may be born with musical deficits is not a new notion, the first documented case of congenital amusia was published only in 2002.
[21] The study was conducted with a female volunteer, referred to as Monica, who declared herself to be musically impaired in response to an advertisement in the newspaper.
Monica also scored above average on a standard intelligence test, and her working memory was evaluated and found to be normal.
Results showed that Monica could barely detect a pitch change as large as two semitones (whole tone), or half steps.
[2] In conclusion, Monica's learning disability arose from a basic problem in pitch discrimination, which is viewed as the origin of congenital amusia.
While a method of treatment for people with amusia has not been defined, tone differentiation techniques have been used on amusic patients with some success.