  We show that synchronism can significantly impact on network behaviours, in
particular by filtering unstable attractors induced by a constraint of
asynchronism. We investigate and classify the different possible impacts that
an addition of synchronism may have on the behaviour of a Boolean automata
network. We show how these relate to some strong specific structural
properties, thus supporting the idea that for most networks, synchronism only
shortcuts asynchronous trajectories. We end with a discussion on the close
relation that apparently exists between sensitivity to synchronism and
non-monotony.
