Amusia

In 1878, Professor Grant Allen reported a man who was unable to perceive differences in pitch. The subject described that attending concerts was similar to sitting in a room for a few hours while nothing happened. Allen later termed his subject’s “auditory abnormality” as note-deafness and his studies became the first record of congenital amusia in medical literature. Amusia is now the common term used to describe learning disabilities related to pitch differentiation, music memory, and music recognition.

Congenital Amusia

To assess the extent of amusia’s effects, in 2001 Dr. Isabelle Peretz performed several behavioral studies on 11 amusic individuals and 20 control subjects. The tests were comprised of individual tones, familiar tunes, lyrics, dissonance, and speech. The results showed that amusia is not caused by complications in the auditory system, since the subjects could readily differentiate speech intonations. Additionally, all the subjects were musically educated as children and adults, ruling out lack of musical exposure as a cause.

Ultimately, amusia was found to be specific to fine-grained pitch perception, which is required to appreciate music but not necessarily speech. This was demonstrated when amusic individuals could not report the difference between original classical pieces and dissonant versions where the pitch was shifted by a semitone. Subjects also had slight difficulties recognizing familiar tunes based on temporal cues such as rhythm. These behavioral studies provided a foundation for determining the neurological basis of amusia.

In 2006, an event-related potential study (ERP) was used to examine the neural wave patterns of amusic individuals. The amusic brain did not respond to pitches that differed by one semi-tone, whereas the brains of control subjects could easily detect the difference. In order to better map the amusic brain, researchers used a neuroimaging technique called voxel-based morphometry, which captures brain images and, using statistical mapping, localizes focal brain points into voxels.

Voxel-based mapping made it clear that amusic individuals had considerably less white matter in their inferior frontal gyrus (IFG) compared to the control.  Likewise, an excess of grey matter was found in the IFG, a characteristic shared by other neurological disorders, such as dyslexia. This provided strong evidence for the involvement of the inferior frontal gyrus in musical pitch encoding and melodic pitch memory. Still, further studies are necessary to verify causation of congenital amusia by the relative levels of white and grey matter in this region of the brain.

Conclusion

To many music lovers, such a disorder might seem like a fate worse than death. Preferences aside, continued research into congenital amusia may provide insight into the neural circuitry underlying our ability to understand and appreciate music while simultaneously exposing the ways improper wiring can cause musical learning disabilities.