Friday, April 19, 2013

The Curious Case of the Earworm (Part 1)

I have had “Thrift Shop” stuck in my head for what seems like days.Yes, it is always on the radio, and yes, I usually listen to it when it is playing. Don't judge me. But why (*Stella scream* wwhhhhyyyyy!) has it established a permanent residence in my brain? I’m going to use a few studies to make the case that it isn’t my fault; I’m led around by my biochemistry. Basically, I’m blaming it on my neurons.

Hmmm…where to start. Let’s try to figure out why we like a song (or music in general) in the first place. A study by Valorie Salimpoor et al. in 2011 suggests that it comes down to the biochemistry of pleasure. We, as humans, as animals, find many things in our lives to be pleasurable. Why is this? Well, our brain tells us so. Pleasure is, in essence, a reward for a good stimulus. In the brain, it is largely mediated by dopamine, which also works to reinforce and motivate these behaviors. Now, most people will agree that music is a pleasurable stimulus, but as an abstract stimulus (one not directly related to survival) is it regulated by the same dopamine pathways? In this 2011 study, subjects were asked to select their own “highly pleasurable music” to play for these tests (since musical preferences are so individualized). Then the researchers used PET scanning to estimate dopamine release. Since there are physiological changes that occur during moments of extreme pleasure, they also used the “chills” or “musical frission” response, an objective phychophysiological measurement of clear and discrete patterns of autonomic nervous system arousal. To tease out the response to the music versus the anticipation of the music, they combined the temporal specificity of functional MRI (through the temporal profile of blood oxygenation level - BOLD) with the neurochemical specificity of the PET scan.

Salimpoor's group found that the pleasure experienced when listening to music is associated with dopamine activity, that there was a positive correlation between the intensity of “chills” and dopamine release, and an increased BOLD response. In fact, dopamine levels surge during key passages of favorite music and just in anticipation of it. This release is pivotal for establishing and maintaining the behavior, making listening to music a valued experience.

Ok, biochemistry…check. Let’s go bigger: What parts of your brain light up when you hear music you like? Salimpoor et al. has published a new study in the April 2013 edition of Science that looks at neural processes active when this pleasurable musical event is happening. Specifically, they look at the reward value the first time a song is heard. We now know that dopamine is involved in familiar music, so what about previously unheard music? To test this, the researchers recruited people, asked them to share their musical tastes (“indie” and “electronic” were the most popular), and used music excerpts selected from a music-recommendation software to pick a unheard song within that preference. To assess reward value, to see if participants liked a song enough that they wanted to hear it again, they were given the option purchase the music with their own money (I know if I have to use my own money then I make sure I love it). Then the participants underwent fMRI scans while listening to musical excerpts and were asked to provide bids of how much they were willing to spend for each song.

The researchers found that the reward value (amount of the bid) was directly related to the region of the brain associated with positive prediction error (the NAcc for you brain folks), or pleasant surprises. Increased functional connectivity with this region was made with the auditory cortices, the region known to play a role in the retrieval of previously stored sound information (STG), and the areas implicated in beat processing (caudate and premotor areas). Additionally, increased connectivity was found in regions associated with emotional processing and value-guided decision-making (VMPFC, OFC, and amygdala), but only when sounds gain reward values. When added to the dopamine findings, the activity in these brain regions suggests that when you hear new music your brain looks at its stored information about sound relationships and makes a decision on whether or not to like it based on previous listening experiences and the expectations of tonal events associated with that type of music. If you like it, then your brain gives you a pleasure reward and you end up using your money to buy the song (or otherwise find ways to hear it again). If you like it better than you expected, you get even more delight.

Now we know why we like the song and want to hear it again (and again and again…).In the next post we will go further and explore what turns this likeable song into an earworm. Or is it its likeablity at all? (insert cliffhanger music here…dun dun duuuunnnn…)

ResearchBlogging.orgSalimpoor, V., Benovoy, M., Larcher, K., Dagher, A., & Zatorre, R. (2011). Anatomically distinct dopamine release during anticipation and experience of peak emotion to music Nature Neuroscience, 14 (2), 257-262 DOI: 10.1038/nn.2726

ResearchBlogging.orgSalimpoor, V., van den Bosch, I., Kovacevic, N., McIntosh, A., Dagher, A., & Zatorre, R. (2013). Interactions Between the Nucleus Accumbens and Auditory Cortices Predict Music Reward Value Science, 340 (6129), 216-219 DOI: 10.1126/science.1231059

...and an article in ScienceNOW "Why Your Brain Loves That New Song"

(image via rockandtheology)

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