an abstract from an article by Isabelle Peretz, Elvira Brattico, Miika Jarvenpaa, and Mari Tervaniemi in Brain. A Journal of Neurology

Like language, music engagement is universal, complex and presentearly in life. However, ~4% of the general population experiencesa lifelong deficit in music perception that cannot be explainedby hearing loss, brain damage, intellectual deficiencies orlack of exposure. This musical disorder, commonly known as tone-deafnessand now termed congenital amusia, affects mostly the melodicpitch dimension. Congenital amusia is hereditary and is associatedwith abnormal grey and white matter in the auditory cortex andthe inferior frontal cortex. In order to relate these anatomicalanomalies to the behavioural expression of the disorder, wemeasured the electrical brain activity of amusic subjects andmatched controls while they monitored melodies for the presenceof pitch anomalies. Contrary to current reports, we show thatthe amusic brain can track quarter-tone pitch differences, exhibitingan early right-lateralized negative brain response. This suggestsnear-normal neural processing of musical pitch incongruitiesin congenital amusia. It is important because it reveals thatthe amusic brain is equipped with the essential neural circuitryto perceive fine-grained pitch differences. What distinguishesthe amusic from the normal brain is the limited awareness ofthis ability and the lack of responsiveness to the semitonechanges that violate musical keys. These findings suggest that,in the amusic brain, the neural pitch representation cannotmake contact with musical pitch knowledge along the auditory-frontalneural pathway.

So, in essence, and pushing this issue a bit further:  this is like autism with regard to music?  Just like an individual with autism who can perfectly well see and hear – but then doesn’t know what to do with this sensory input (what does it mean when someone “smiles”??), an individual with an amusic brain can hear and distinguish musical details just as well as everyone else – but what is being heard has no meaning because there is no “contact with music pitch knowledge” due to a “lack of responsiveness”.

The question, as always, is:  what do we do – now that we know?