  Within the framework of the internal-external shocks model for gamma-ray
bursts, we study the various mechanisms that can give rise to quiescent times
in the observed gamma-ray light-curves. In particular, we look for the
signatures that can provide us with evidence as to whether or not the central
engine goes dormant for a period of time comparable to the duration of the
gaps. We show that the properties of the prompt gamma-ray and X-ray emission
can in principle determine whether the quiescent episodes are due to a
modulated relativistic wind or a switching off of the central engine. We
suggest that detailed observations of the prompt afterglow emission from the
reverse shock will strongly constrain the possible mechanisms for the
production of quiescent times in gamma-ray bursts.
