Amusia and stroke

Although a complete musical anti-talent myself, that doesn’t prohibit me from fully enjoying the works of the masters in the art. When my family is out of earshot, I even bellow – because it cannot be called music – from the top of my lungs alongside the most famous tenors ever recorded. A couple of days ago I loaded one of my most eclectic playlists. While remembering my younger days as an Iron Maiden concert goer (I never said I listen only to classical music :D) and screaming the “Fear of the Dark” chorus, I wondered what’s new on the front of music processing in the brain.

And I found an interesting recent paper about amusia. Amusia is, as those of you with ancient Greek proclivities might have surmised, a deficit in the perception of music, mainly the pitch but sometimes rhythm and other aspects of music. A small percentage of the population is born with it, but a whooping 35 to 69% of stroke survivors exhibit the disorder.

So Sihvonen et al. (2016) decided to take a closer look at this phenomenon with the help of 77 stroke patients. These patients had an MRI scan within the first 3 weeks following stroke and another one 6 months poststroke. They also completed a behavioral test for amusia within the first 3 weeks following stroke and again 3 months later. For reasons undisclosed, and thus raising my eyebrows, the behavioral assessment was not performed at 6 months poststroke, nor an MRI at the 3 months follow-up. It would be nice to have had behavioral assessment with brain images at the same time because a lot can happen in weeks, let alone months after a stroke.

Nevertheless, the authors used a novel way to look at the brain pictures, called voxel-based lesion-symptom mapping (VLSM). Well, is not really novel, it’s been around for 15 years or so. Basically, to ascertain the function of a brain region, researchers either get people with a specific brain lesion and then look for a behavioral deficit or get a symptom and then they look for a brain lesion. Both approaches have distinct advantages but also disadvantages (see Bates et al., 2003). To overcome the disadvantages of these methods, enter the scene VLSM, which is a mathematical/statistical gimmick that allows you to explore the relationship between brain and function without forming preconceived ideas, i.e. without forcing dichotomous categories. They also looked at voxel-based morphometry (VBM), which a fancy way of saying they looked to see if the grey and white matter differ over time in the brains of their subjects.

After much analyses, Sihvonen et al. (2016) conclude that the damage to the right hemisphere is more likely conducive to amusia, as opposed to aphasia which is due mainly to damage to the left hemisphere. More specifically,

“damage to the right temporal areas, insula, and putamen forms the crucial neural substrate for acquired amusia after stroke. Persistent amusia is associated with further [grey matter] atrophy in the right superior temporal gyrus (STG) and middle temporal gyrus (MTG), locating more anteriorly for rhythm amusia and more posteriorly for pitch amusia.”

The more we know, the better chances we have to improve treatments for people.

104-copy

unless you’re left-handed, then things are reversed.

References:

1. Sihvonen AJ, Ripollés P, Leo V, Rodríguez-Fornells A, Soinila S, & Särkämö T. (24 Aug 2016). Neural Basis of Acquired Amusia and Its Recovery after Stroke. Journal of Neuroscience, 36(34):8872-8881. PMID: 27559169, DOI: 10.1523/JNEUROSCI.0709-16.2016. ARTICLE  | FULLTEXT PDF

2.Bates E, Wilson SM, Saygin AP, Dick F, Sereno MI, Knight RT, & Dronkers NF (May 2003). Voxel-based lesion-symptom mapping. Nature Neuroscience, 6(5):448-50. PMID: 12704393, DOI: 10.1038/nn1050. ARTICLE

By Neuronicus, 9 November 2016

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