The Journal of Neuroscience, November 15, 1999, 19(22):10074-10081
Neural Representation of a Rhythm Depends on Its Interval
Ratio
Katsuyuki
Sakai1, 2,
Okihide
Hikosaka1,
Satoru
Miyauchi3,
Ryousuke
Takino4,
Tomoe
Tamada5,
Nobue Kobayashi
Iwata2, and
Mathew
Nielsen3
1 Department of Physiology, Juntendo University School
of Medicine, Tokyo 113-0033, Japan, 2 Department of
Neurology, Division of Neuroscience, Graduate School of Medicine,
University of Tokyo, Tokyo 113-0033, Japan,
3 Communications Research Laboratory, Kobe 651-24, Japan,
4 Shiraume Gakuen College, Tokyo 187-8570, Japan, and
5 Exploratory Research for Advanced Technology, Japan
Science and Technology Corporation, Kyoto 619-02, Japan
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 representation for rhythms formed
with small integer ratios and noninteger ratios, respectively. We used
functional magnetic resonance 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 intervals. The results showed two patterns
of brain activations; the left premotor and parietal areas and right
cerebellar anterior lobe were active for 1:2:4 and 1:2:3 rhythms,
whereas the right prefrontal, premotor, and parietal areas together
with the bilateral cerebellar posterior lobe were active for 1:2.5:3.5
rhythm. Analysis on individual subjects revealed that these activation
patterns depended on the ratio of the rhythms that were produced by the subjects rather than the ratio of the presented rhythms, suggesting that the observed activations reflected the internal representation of
rhythm. These results suggested that there are two neural
representations for rhythm depending on the interval ratio, which
correspond to metrical and nonmetrical representations.
Key words:
rhythm; short-term memory; metrical representation; nonmetrical representation; interval ratio; cerebellar anterior lobe; cerebellar posterior lobe; right hemisphere; left hemisphere
Copyright © 1999 Society for Neuroscience 0270-6474/99/192210074-08$05.00/0
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