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Abstract:
Abstract: Ivry (1996) suggested that the timing of short (ms)
intervals involves the cerebellum whilst long (seconds or longer)
intervals engage the basal ganglia and frontal cortex. We tested
this hypothesis using H215O PET. Prior to scanning, the 8 subjects
were familiarised with 'short' (500ms) and 'long' (2s) intervals
marked by 50ms onset and offset tones. During scanning subjects
performed three tasks: short interval estimation, long interval
estimation and a control reaction time task. In the timing
conditions, a 50ms tone marked interval onset and subjects
estimated the long or short interval then pressed a response button
to mark the offset. In the control condition subjects pressed the
response button as soon as possible after tone presentation. Tone
presentation rate was identical across conditions. Short interval
estimation increased rCBF in anterior cingulate, middle temporal
gyrus, SMA, superior frontal gyrus, the superior and mesial frontal
gyrus, caudate nucleus and cerebellum. Long interval estimation
significantly activated lateral premotor cortex, SMA, anterior
cingulate, dorsolateral prefrontal cortex, putamen and cerebellum.
More posteriorally, superior and inferior parietal cortex and
cuneus were also activated. The findings do not support the
hypothesis but suggest that fronto-striatal areas and the
cerebellum are significantly activated with estimation of long and
short intervals, while more posterior areas are activated during
estimation of long intervals.
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