Neuropsychology

Brains out of tune

Is lack of musical ability simply the result of failure to practise? Probably not, if new investigations are anything to go by. They show that a disorder akin to dyslexia affects the processing of pitch.

There was an old fellow of Sheen whose musical sense was not keen. He said: “It is odd, I can never tell 'God save the weasel' from 'Pop goes the Queen'!”

The old fellow of Sheen was in good company. Two presidents of the United States, Ulysses S. Grant (Fig. 1) and Theodore Roosevelt1, were tone deaf, as was Che Guevara2. Music educators often ascribe3 lack of musical aptitude to lack of practice. But in a paper published in Brain4, accompanied by a case report in Neuron5, Isabelle Peretz and colleagues suggest that 'congenital amusia' is a developmental disorder that can be placed alongside developmental dyslexia and specific language impairment.

Figure 1: “I only know two tunes.
figure1

BETTMANN/CORBIS Inset: CORBIS

One of them is Yankee Doodle and the other isn't.” So said the tone-deaf Ulysses S. Grant (inset) to a reporter. Music annoyed Grant, so the band shown here, playing at his second inauguration in 1873, is unlikely to have set his toes tapping. Peretz and colleagues4,5 consider such 'congenital amusia' to be due to impaired processing of musical pitch.

The possibility that people can be subject to a selective, potentially inborn deficit of music processing has been entertained for more than a hundred years. But there have been only a few anecdotal reports to support such a notion. For example, the neuropsychologist Norman Geschwind described6 a man from a family with several musically impaired members who was fluent in three foreign languages yet could not sing a song, discriminate the pitch of two tones, or keep a rhythm, despite having had music lessons as a child.

Peretz and colleagues4,5 set out to put these observations on firmer grounds. To rule out a general learning disorder, they selected 11 subjects from a larger group of self-declared unmusical volunteers who had achieved a high level of education, had been exposed to music during childhood lessons, and had been unsuccessful in mastering music from the start. Previous research has shown that memory for songs and different aspects of music — such as interval (the pitch difference between two tones), contour (the general direction in which a melody is moving), rhythm (the local temporal structure of a piece) and metre (its global temporal structure) — can be distinguished and are selectively impaired in patients with damage to particular parts of their brain7.

When their unmusical subjects were given a standardized battery of tests assessing these different dimensions, Peretz and co-workers found that there was a general failure in those tests involving pitch perception, whereas results in rhythm and metre tasks were more varied. In addition, the unmusical subjects were also insensitive to distortions of familiar tunes, and indifferent to dissonant chords. But they had no problem in recognizing familiar voices, environmental sounds and song lyrics. So a pitch-processing deficit was at the heart of the subjects' problems.

Peretz and colleagues next asked whether this deficit is specific to music, or whether it extends to other domains that depend on pitch information, such as language. In spoken language, crucial information is transmitted by modulating the pitch contour, or prosody. Consider, for example, the differences in intonation between “She is rich?” and “She is rich.” Questions are indicated by a final rise in pitch of the order of six semitones, whereas for statements the pitch falls by about three semitones. The unmusical subjects had no difficulties in picking up these differences — that is, they could detect whether a stimulus was spoken as a question or as a statement — which suggests that the deficit is selective for music-like stimuli and spares the language domain.

What is the cause of this remarkable disturbance in pitch processing? Is it congenital, as Peretz and colleagues maintain? And if so, does it indicate the existence of a specific, genetically determined music-processing system? In support of the view that the deficit is hereditary, the authors point out that 6 of the 11 subjects described one of their parents, as well as some of their siblings, as unmusical, with other family members being said to be 'normal' musically.

These family histories hardly qualify as hard evidence. But fortunately it turns out that, as far back as 1925, geneticists found evidence for the heritability of pitch discrimination8. Last year, this issue was re-examined by Drayna et al.9 using state-of-the-art genetic modelling on a large sample of identical (monozygotic) and fraternal (dizygotic) twins in Britain. Such twin studies allow the influence of shared environments to be separated from that of shared genes. Drayna et al.9 presented subjects with a set of simple popular tunes, some of which had been altered by inserting a wrong note. The subjects differed greatly in their ability to detect the altered melodies, and genetic model-fitting indicated a heritability of pitch discrimination of 70–80%.

Does this mean, then, that the basic building-blocks of our music-processing system are to a large part inherited? Hundreds of pages have been filled over the past 150 years with attempts to explain the appearance of music, starting with Charles Darwin10, who believed that systems of calling in animals have a musical quality and evolved into speech. This view is echoed in a recent article by Gray et al.11, which draws parallels between the songs of birds, whales and humans. Steven Pinker, the outspoken cognitive neuroscientist, on the other hand, notes that “of [all] mental faculties... music shows the clearest signs of not being [adaptive]”12 and probably occurred as an epiphenomenon, as “auditory cheesecake”.

The new data provided by Peretz et al.4,5 establish congenital amusia as a specific developmental disorder. But to go further and help settle the debate, combined behavioural and genetic study of subjects with music-processing deficits will be needed to reveal more about the biological origins of our musical faculty.

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Correspondence to Thomas F. Münte.

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Münte, T. Brains out of tune. Nature 415, 589–590 (2002). https://doi.org/10.1038/415589a

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