Neural Representation of a Rhythm Depends on Its Interval Ratio

Rhythm is determined solely by the relationship between the time intervals of a series of events. Psychological studies have proposed two types of rhythm representation depending on the interval ratio of the rhythm: metrical and nonmetrical represen-tation for rhythms formed with small integer ratios and nonin-teger ratios, respectively. We used functional magnetic reso-nance imaging to test whether there are two neural representations of rhythm depending on the interval ratio. The subjects performed a short-term memory task for a seven-tone rhythm sequence, which was formed with 1:2:4, 1:2:3, or 1:2.5: 3.5 ratios. The brain activities during the memory delay period were measured and compared with those during the retention of a control tone sequence, which had constant intertone inter-vals. The results showed two patterns of brain activations; the left premotor and parietal areas and right cerebellar anterio