  The continuum variability of optically selected Active Galactic Nuclei (AGN)
is found to be consistent with that expected from a simple Poissonian process,
in which the total luminosity of an object is produced by the multiple
superposition of identical pulses. The energies, time-scales and rates of the
pulses are found to be in the range of those expected from supernovae which
generate fast evolving remnants in a nuclear starburst.However, radio-loud AGN
don't follow the predictions of that simple scenario.
