Neural Representations of Beat and Rhythm in Motor and Association Regions

Humans perceive a pulse, or beat, underlying musical rhythm. Beat strength correlates with activity in the basal ganglia and SMA, suggesting these regions support beat perception. However, the basal ganglia and SMA make up a general timing network active during rhythm and timing perception, regardless of beat. Therefore, activity in these regions may represent basic rhythmic features, in addition to beat. Using RSA, we characterized the neural representation of rhythm in the basal ganglia, SMA, and across the whole brain. During fMRI, participants heard 12 rhythms - 4 strong-beat, 4 weak-beat, and 4 non-beat. Multi-voxel activity patterns for each rhythm, and for the mean of each condition, were tested for uniqueness. Activity patterns in beat-sensitive regions should alter as a function of beat strength, eliciting greater dissimilarities between rhythms with different beat strength than between rhythms with similar beat strength. Indeed, mean activity patterns in the putamen and SMA were significantly dissimilar for strong-beat and non-beat conditions, and dissimilarity between activity patterns across all 12 rhythms correlated with beat strength models, not basic rhythmic features. Whole-brain analyses also identified beat-sensitivity in the IFG, and inferior parietal cortex. These findings build upon univariate work suggesting that motor and association regions are beat-sensitive.