  We report experimental observations of the core dynamics of multi-armed,
rotating spirals in Rayleigh-Benard convection for a fluid with Prandtl number
near one. In addition to the large-scale rotation of the spirals, we found a
cyclic core motion within a central area of radius r = appr. (n lambda/2),
where n is the number of spiral arms ending in the core and lambda is the
wavelength of the pattern. The dynamics of the core was much faster than the
large-scale spiral rotation. We observed multi-armed spirals for which the two
periods were commensurate and others for which they were incommensurate.
