“Tone Deaf”-
A review on Congenital Amusia
By Lena Meredith
We’ve all got a “tone-deaf” friend, right? You play that song in the car that everyone wants to sing along to, and somehow you can always hear that one person who, no matter the circumstance, sings along but just can’t seem to stay in the key or sing the correct pitch? As it turns out, this isn’t just your friend being a terrible singer. If they truly are unable to match pitches and sing along, they could have something called congenital amusia. Isabelle Peretz defines this as “lifelong musical disabilities that cannot be attributed to intellectual disability, lack of exposure, or brain damage after birth” (Peretz, 2016). Now, note that while this includes pitch malfunctions, it can be so much worse. In his book Musicophila, author Oliver Sacks recounts his experience with a woman who had severe congenital amusia. She described all music simply as the banging of pots and pans, which was of course a horribly unpleasant experience that she could not understand for most of her life.
This link is a brief interview with Oliver Sacks about amusia from his book –
https://www.youtube.com/watch?v=dtkfaroKDfI&feature=youtu.be
So what is it, really? Isabelle Peretz discusses amusia in her paper Neurobiology of Congenital Amusia, which was published in 2016. To clarify, the term “congenital” just means it has been present since birth. Though there are other types, the most common form of congenital amusia is the classic tone-deafness we all think of, which affects around 4.2% of the world’s population. Amusia is also hereditary, so it can be passed down from previous generations.
In her paper, Peretz discusses many aspects of congenital amusia, which first and foremost, is musical pitch. Amusics (those with this condition) cannot recognize a pitch change smaller than two semitones. Semitones are simply half steps in western tonal music, or the distance between the pitch of two keys on a piano. Amusics cannot recognize any change less than two of these half steps. The fascinating thing about this disorder is that it doesn’t usually coincide with any kind of speech disorder, despite the fact that speech also involves small pitch changes (although amusics do struggle with subtle tonal changes in speech).
Here’s how they tested pitch perception — the brain responds to abnormalities in any kind of pattern with something called a mismatch negativity (MMN) response, which happens very early in the overall process of auditory processing. This applies to tonal changes, so one study looked at brain responses in amusics to tonal mismatches. Interestingly enough, fMRI studies have shown amusics do have MMN responses, meaning their brain does recognize this small pitch change, but they do not consciously notice it. In other words, this form of amusia involves a disconnect between what the brain automatically responds to and the person’s ability to actually draw on this information and consciously report it (so the deficit happens later in the process). They could even often report to a researcher if the interval they heard went up or down, so somehow these “detection” neural systems are separate from these “action” neural systems.
Let’s not forgot that amusics can still enjoy music. In fact, very few amusics deprive themselves of all music. Only the most extreme cases (like the woman interviewed by Oliver Sacks) find all music to be displeasing, incoherent sounds thrown together. The average person with congenital amusia can still recognize large pitch changes in addition to tempo, timbre, key clarity, etc., and as such music can still affect their emotions and their internal state.
This next part may get tricky but bear with me — what’s happening here in an amusic’s brain? We know there’s a disconnect between pitch detection and conscious recognition, but where does that actually occur? Peretz mentioned abnormalities in the brain of amusics in the inferior frontal gyrus (IFG) and the auditory cortex, as well as disrupted communication between these two areas. Essentially, each of these areas have a higher amount of grey matter than normal (more synapses and general “processing power” than normal). The tract between these two areas, called the right arcuate fasciculus, has reduced volume. This means there is a deficit when it comes to communication between the IFG and the auditory cortex, which Peretz says could be to blame for congenital amusia.
The figure above demonstrates the pathway of information (left flowchart) that shows sound input from the cochlea in the ear to the brainstem to the primary auditory cortex (A1) to the superior temporal gyrus (STG) to the inferior frontal gyrus (IFG). As shown, amusics have complications within the arcuate fasciculus (right picture), which connects A1 and the IFG.
The flow chart also demonstrates a feedback loop. In an average individual, this feedback loop would be used to, for example, adjust their singing when they hear they are off key. In amusics, this feedback loop is disrupted, which has to do with their inability to judge their pitch accuracy and keep it in their memory.
Peretz goes on to discuss how congenital amusia is related to prosopagnosia (the inability to recognize faces) and dyslexia (an impairment in acquiring reading skills). All three of these disorders involve many different networks in the brain and are all caused by a disruption of some sort of connection from one relevant region to the next. With amusia specifically, Peretz emphasized it’s not something that only involves the auditory cortex as one might initially think but that the IFG is very relevant as well. While there is, unfortunately, no currently known way for amusics to improve in their recognition of small pitch differences, most amusics still can and do enjoy music and incorporate it into their lives.
References -
Peretz, I. (2016). Neurobiology of Congenital Amusia. Trends in Cognitive Sciences, 20(11), 857–67.
Sacks, O. (2007). Musicophilia: Tales of Music and the Brain. Knopf Doubleday Publishing Group.
