Let me begin with a personal reflection. I think the human brain has a mission that sets it apart from other species. Our mission is to create brain. All cultures and for thousands of years in the beginning of our history as a species have needed to carve, paint, sing or tell beautiful stories.
Unfortunately we need to eat and for this hunt and work, health and for that we need doctors, nurses ... we need to take shelter or harbor and that makes it "distracted" the brain from its main function but retain the need to be creative in our work.
At present we ignore the "biological purpose 'music has probably its biological function is vital for social cohesion and its advantage is not individual but the collective ( 1 ). Although only a few individuals become expert musicians all have experience of it, even to become avid listeners since childhood.
In every culture the experience that produces the music is similar. Establish a communication system aimed primarily at the emotions of the listener, can arouse emotional responses in a subject not specifically trained for listening to music, although you could say that we all suffer in some way a 'cultural amusia' for some perception of melodies are highly valued in one culture but foreign in others.
Similar to what happens with verbal language functions, music and language are based on a common structural basis in the cerebral cortex responsible for processing, we also know that there are neural mechanisms for processing different linguistic activity, conditioned by the difference in the structure of language literacy in different cultures, with the example shown the unique expression of aphasia in patients who use a language based on ideograms such as Chinese and Japanese. On this basis, we might think that just happens to language, more or less selective lesions can produce defects in perception or production of music.
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The term " amusia "we owe it to Knoblauch also first designed a model cognitive processing of music based on a model diagrammatic , as has been done with the linguistic processes. He assumed that only occur in amusia musicians ( 2 ).
Amusia is defined as a neurological defect involves an alteration in auditory perception, reading, writing and musical performance and is not due to motor or sensory impairment. The term is usually reserved for defects that appear isolated and are due to a focal lesion or at least initially focal, being less used when the defect is related to dementia or psychiatric illness. Is the term used to describe congenital amusia subjects who are unable to recognize the melodies or discriminate the difference between the tones, but have no other neurological defect and having had adequate exposure to ambient music ( 3 ).
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If you mean by "language" the human ability to communicate his thoughts or feelings may mean the term deficits amusia "language", especially for subjects who have received some degree of schooling in this field. Moreover, the execution of a score requires significant training activity that facilitates automation of the motor act to be smooth and harmonious using either an instrument or voice.
Amusia is a very rare cause for complaint, except as professional musicians or music lovers in the functional defect that cause is sufficiently low, however in recent years, interest in the systematic search for these patients has led to better understanding of some phenomena in the processing of music.
As for the musical information processing requires the involvement of both frontal and temporal lobes, injury amusia can appear in any of them on a unilateral or bilateral, it probably does so systematically explored such as language or motor activity, would verify that it is a much more common than we think.
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It is important to understand what we mean when we use the word music. If we define as "the art of combining sounds in time", any type of sound produced by any object, used properly, can be interpreted as music, and is characterized by the combination of different tones (the variation in a determined sequence produces the melody) in a time sequence of variable duration (rhythm) and differentiated in different rings (due to different harmonics produced by each instrument), can be developed at different speeds.
Singing is a skill that is acquired early in childhood ( 4 ) and probably because our first source is the maternal singing is highly satisfactory against the general statements is a skill spread evenly across the population, if we refer to familiar tunes and well known in the environment, maintaining accurate memories of both melody and rhythm, but the ability of each subject can be variable ( 5 ).
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The amusia are more than agnosia but in general, patients with auditory agnosia also have some degree of amusia, especially patients with non-verbal agnosia content, however there are patients with agnosia for music that can identify other non-verbal sounds ( 6 ) or can identify the music, despite the difficulty in understanding environmental sounds ( 7 ). This suggests that there is a more or less specific and differential for music and for sound environmental sounds or verbal content of these mechanisms being qualitatively and quantitatively different.
Like with auditory agnosia is important to remember that the representation of auditory stimuli is bicortical, with variability between individuals and a certain degree of contralateral preference representation, so frequently as in other modalities auditory agnosia appears after bitemporal lesions, although there are cases described by unilateral injury. In this regard it is important to note that the right hemisphere may perform simple procedures such as extraction of tone but more complex processes like the melodic and rhythmic organization require the activity of the left hemisphere ( 8 ).
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The identification of the melody of a well-known piece of music is mainly based on the recognition of the correct alternation of tones with a relative distance between them that allows us to discriminate between the most acute and most serious, this distance should be kept even if we change starting tone, it is so important that the initial note is "do" or "F" if the relative distances with the following notes is the same in both cases identify the same piece as it retains the same melodic scheme. Then we need to identify the song in our repertoire of familiar tunes like lexicons need to identify with our verbal language, which implies the existence of an abstract representation and a storage system of tones that the subject is able to recognize.
Probably sounds with common characteristics or similar frequency are grouped as a single auditory object ( 15 ). A change in the emission rate in the timbre of the instrument or rate does not produce a significant distortion in the recognition of the part, an error in the sequence of tones will be recognized as foreign to the part and if it is sufficiently important can reach to prevent identification.
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With regard to the perception of one component of the melody, pitch, we do not know the exact mechanism used. Except for the few individuals who possess the ability to discriminate and therefore heard correctly name a single tone which is what is called "absolute pitch" ( 9 ), we perceive and isolated pure tones (which would be independent of melodic contour) is its more or less rapid sequencing which allows us to distinguish distances between a tone and the next, we perceive therefore fundamentally tonal grouping units that behave somewhat similarly to a compound word by the grouping of different sounds (letters ).
Thus a score are 'reasons' which are grouped into "sentences" pronounced a certain way, which identifies the temporary component of it, and are easily identifiable when they reappear in the course of the piece though be modified in the other components "non core" (rhythm, timbre, etc.)..
By way of example, can be heard here two instrumental versions of the British national anthem. They have different pitch and speed (the second is faster and a little more serious tone), but both are clearly "God Save the Queen": listen to the version 1 , and then can listen to the version 2 .
Also drawn up separately the perception of the temporal process of the melody ( 1 ), but later integrate both sequence information for the musical. There is one reported case of a musician following a heart attack suffered a right temporoparietal amusia hard to discriminate and reproduce new sounds, suggesting that the right temporal lobe has a higher activity for this function ( 10 ).
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Obviously, this ability of perception of time intervals is independent of the technical knowledge of music and that training can provide us with your purchase, thus allowing playback interval sequences leading to the ability that in Spain is called "sing by ear." It is important to remember that the slight modification of these time intervals as lengthening the end of a sentence, slow down a passage, and so on., Facilitates emotional component in the expression of music, for this reason it can make a very moving musical performance without need to be a 'knower schooled "in the same.
In fact, at least in the cultural environment of the authors, the interpreters of popular song and a very marked passion component (the most typical example is the flamenco music) often have they learned to sing listening to "their elders" and have never studied music. His ability to convey affection is even higher than in school musicians ( 11 ). It is possible that this may be facilitated by greater use of the right hemisphere when developing his musical activity with respect to school musicians for the musical language, using analytical components in the process of perception of music with the participation of the hemisphere left ( 12 ).
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Figure reproduced with permission. License number: 2060361286595. From: Robert J. Zatorre, Joyce L. Chen and Virginia B. Penhune. When the brain plays music: auditory-motor perception and Interactions in music production. Nature Reviews Neuroscience 2007, 8 (7) :547-558. © Nature Publishing Group 2007.
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Studies comparing the perception of melody between musicians and non-musicians shows that musicians have a better sense of melody with their right ear while non-musicians show a dominance in the left ear perception probably because this function is so processed different in both. If we consider that musicians can discriminate the difference between two tones is likely to accurately identify melodic sequences using their ability to distinguish intervals (most characteristic activity of the left hemisphere), while non-musicians receive the melody more holistic (which is defined as the contour of the melody) why there is a difference between groups in the dominance of the cerebral hemispheres in processing the melody ( 13 ).
The understanding of music thus implies sequential analysis and the overall ( gestalt ) information with bi-hemispheric activity probably cooperating in her left hemisphere for analytic components and the right in the emotional components more intense than in speech. It is possible that the perception of 'natural' music is located in the right hemisphere, dominant in the perception of musical material of the tunes, and let their professional learning and the holistic and analytical acquired at various levels of musical structure making certain functions to be assumed by the left hemisphere because of their greater expertise to the analysis of temporal patterns. However, according to the tasks and the stimuli presented and of course subjects, lateralization may vary.
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If we admit that there is a system of reading and writing, which allows us to understand and reproduce the same way by different readers the same information and communication component that has a clear, in my opinion there is no doubt that the music for a subject "schooled" it has all the characteristics that define a language, therefore the rational thing would be that the musicians are bilingual subjects presenting the peculiarity of using an alphabetic script language and another in which the visuospatial component is paramount. The notation can not be considered strictly ideographic, so that the musicians really amusia have a similar behavior to some of bilingual aphasia. Professionals schooled in the musical language of injuries affecting the left hemisphere, in the case of musicians (professional or otherwise) who can not read or write music the lesion involves the right hemisphere.
We may have to rethink the concept of amusia and consider only those defects as such or issue of perception of music in non-formal learning under the same, although some emotional component disperceptivos problems or his own " musicality 'of music to be common in both groups and consider the musical language aphasias for defects that appear in the subject readers-writers own peculiar language.
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Briefly discuss a clinical case.
The first case of a discrepancy between verbal and musical language was made in 1745. The patient had hemiparesis with aphasia right, could only say "yes", but could sing hymns already learned, both in its melody and the lyrics and can continue singing a hymn to initiate the examiner. This same patient preserved automatic speech in the sense that he could recite prayers without singing, as long as the "recite" with a sense of rhythm.
Since then, there are many quotes from people with aphasia and preservation of singing with or without words, with or without altering the perception of tone or rhythm, being the most frequent description of subjects with aphasia in which the issue was preserved well-known songs.
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The best known case of amusia by their social impact is that of Maurice Ravel. Was studied in 1948 by Alajouanine ( 14 ). She presented apraxia ideomotor, alexia , agraphia and aphasia Wernicke and probably suffered from frontotemporal dementia can be a primary progressive aphasia, but described apraxia could be a corticobasal degeneration. At the start of their symptoms predominated aphasic symptoms and the difficulty to produce music. In the original description refers to a syndrome in which progressive evolution Alajouanine uses the phrase "memory, trial, affection and aesthetic taste were intact" and so was notified that the "musical thinking" was able to recognize melodies tones, deliberately introduced errors in a score for the tones and rhythms, yet was unable to sing or play the piano, either spontaneously or by imitation and dictation, he could not nominate, sing or play written notes, could write music but This content was very poor, but better than the writing of words and the copy was virtually impossible. Refer attending concerts and maintain clear and gaining critical listening pleasure of it and apparently could devise his compositions properly. Famously Ravel which describes itself "I have a head full of music but I can not write."
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Another well-known case, probably for the same reasons although its popularity is much lower, is the Russian composer Shebalin studied by Luria in 1965 ( 15 ), suffered a first vascular event with right hemiparesis and aphasia that evolved favorably. After this episode and wrote actively for 6 years and even led the Moscow Conservatory. Suffered another stroke , which is what Luria attended, which resulted in a Wernicke aphasia with abundant paraphasias .
After a slight initial improvement in functional defect caused a relatively important throughout his life, with alexia and agraphia, was able to continue composing, as their peers with the same skill as always, Shostakovich Symphony V said of her that:
"He was a brilliant and creative work, full of high emotions, optimistic and full of life. This symphony composed during his illness, is the creation of a great teacher. "
Apparently had a large temporal and parietal lesion postsangrado lower left. It is obvious that a defect in understanding the spoken language does not have to interfere with the ideation of musical language, otherwise it would be like asserting that a patient with Wernicke's aphasia can not develop ideas.
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Handel suffered several strokes with right hemiparesis and aphasia interrupting its activity as a songwriter after all but was able to take it up forever, even after the third, which describes that "lost his creativity," but he could re-enter months later.
Haydn featured a story about 8 years of evolution of gait disturbance, character change, depression , memory loss, "there are days when I lose the ideas" that made it less and composing more slowly. In his last two years was frank dementia. Presented during his illness episodes that may correspond with transient ischemic attacks so it is possible that his disease was a vascular dementia subcortical.
I would speculate that the syndrome of Gilles de la Tourette Mozart probably would have suffered some impact on his creativity, after all the neurotransmitter dopamine is involved in the control of emotion, but that's another story.
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