How your brain helps you get your groove on

I wrote this for a science writing competition. I did not win (here is the piece that won for the journal article I chose to explain), so I am publishing my entry here.

The paper (it’s open access, so no paywalls!): Grahn, J.A. & Rowe, J.B. (2013) Finding and feeling the musical beat: Striatal dissociations between detection and prediction of regularity. Cerebral Cortex23(4), 913-921.

The abstract: I’m going to start putting these at the end of my post because I am conceited and think you should read my explanation first.

At some point in our lives, we have likely all encountered That Guy or That Gal who just can’t seem to dance to a beat. That Guy is often found on the dance floor at a wedding reception, flailing his limbs with wild abandon but no regularity. That Gal may be in your Zumba class, perpetually a quarter to a half-second behind the music while the rest of the class is shaking their hips in sync. Why can’t That Guy and That Gal just get with the beat?

Hint: look towards the back of the room.

Did you find That Gal? Image from Brittany Carlson, Wikimedia Commons

Being able to recognize a musical beat requires two things. First, one must be able to find the beat – the steady time intervals that underlie a piece of music or rhythmic sequence. Second, one must be able to maintain an internal sense of that beat as the music continues.

The ability to find a beat lets you start dancing in time to the music, while the ability to maintain a beat lets you continue moving your limbs in a regular fashion as the music plays on. Researchers at the University of Western Ontario and Cambridge University have found that we use one part of our brain, the cerebellum, to look for the beat, and another part of our brain, the basal ganglia, to maintain it.

In the study by neuroscientists Jessica Grahn and James Rowe, 24 healthy adults listened to a series of rhythms while their brain function was measured using magnetic resonance imaging. Some of the rhythms had underlying beats of a variety of tempos. Others had no underlying beat whatsoever.

In a clever design twist, the different rhythms were consecutively strung together so that sometimes the beat stayed the same while the rhythm changed, sometimes the beat became faster or slower, sometimes the beat disappeared entirely, and sometimes a beat emerged from a beat-less rhythm. This design allowed the experimenters to measure how brain function changed when participants searched for a beat when there was none to find or when an existing beat was continued or altered in a new rhythm.

I also developed a strong lower back.

I developed excellent beat finding skills on my college drumline.

The cerebellum, a brain structure that sits right above the spinal cord, was more active when participants listened to rhythms that lacked a beat than when they listened to rhythms with a beat. The neuroscientists interpreted this to mean that the cerebellum is looking for a beat before a regular rhythm can be detected. Scientists already know that the cerebellum helps coordinate our motor movements, and this study suggests that it does so in part by paying extra attention to irregular timing.

In contrast, another part of the brain called the basal ganglia was more active when listening to beat rhythms than when listening to non-beat rhythms. Furthermore, its activity level differed depending on the relative tempos of the rhythms: it was active when a beat changed tempo to become faster or slower, it was even more active when a beat maintained the same tempo but switched to a new rhythm, and it was most active when both the current beat and current rhythm stayed the same.

My, what lovely ROIs you have!

The basal ganglia (in hot colors) maintains our sense of the beat. From Figure 7 of the paper.

Finally, the basal ganglia did not differentiate between a non-beat rhythm and the first appearance of a rhythm with a beat, indicating that the basal ganglia do not pay attention to the emerging presence of a beat when there was none before. This graded level of activity in the basal ganglia suggests that it works to maintain our sense of the beat and favors continuity and similarity – it works the hardest when it meets a reliable rhythm and slacks off a bit as the rhythm changes.

Note that putamen is NOT pronounced put-a-men.

Structures in the left and right basal ganglia show no significant responses to the presence of a new beat but do show significant responses to existing beats, even if they’re changing. From Figure 7 in the paper.

Scientists already know that the basal ganglia play an important role in generating and maintaining movement, as well as in learning and reward processing. Movement disorders such as Parkinson’s disease, in which patients have difficulty initiating movement, and Huntington’s disease, in which patients have difficulty stopping and controlling movements, are both linked to damage to the basal ganglia.

Understanding exactly how different parts of the brain enable us to control and coordinate our movements helps scientists figure out what deficits to expect from people with neurological damage and how those deficits could be treated. As a result of this study, we now know that healthy basal ganglia let us maintain our sense of regular rhythm – a sense that is important for anything that involves syncing movement to a regular beat, including walking, speaking, and, of course, dancing like a champ.

The abstract: Perception of temporal patterns is critical for speech, movement, and music. In the auditory domain, perception of a regular pulse, or beat, within a sequence of temporal intervals is associated with basal ganglia activity. Two alternative accounts of this striatal activity are possible: “searching” for temporal regularity in early stimulus processing stages or “prediction’ of the timing of future tones after the beat is found (relying on continuation of an internally generated beat). To resolve between these accounts, we used functional magnetic resonance imaging (fMRI) to investigate different stages of beat perception. Participants heard a series of beat and nonbeat (irregular) monotone sequences. For each sequence, the preceding sequence provided a temporal beat context for the following sequence. Beat sequences were preceded by nonbeat sequences, requiring the beat to be found anew (“beat finding” condition), or by beat sequences with the same beat rate (“beat continuation”), or a different rate (“beat adjustment”). Detection of regularity is highest during beat finding, whereas generation and prediction are highest during beat continuation. We found the greatest striatal activity for beat continuation, less for beat adjustment, and the least for beat finding. Thus, the basal ganglia’s response profile suggests a role in beat prediction, not in beat finding.

ResearchBlogging.orgGrahn, J., & Rowe, J. (2012). Finding and Feeling the Musical Beat: Striatal Dissociations between Detection and Prediction of Regularity Cerebral Cortex, 23 (4), 913-921 DOI: 10.1093/cercor/bhs083

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