  We use classical molecular dynamics simulations to study the dynamics of
sodium atoms in amorphous Na$_2$O-4SiO$_2$. We find that the sodium
trajectories form a well connected network of pockets and channels. Inside
these channels the motion of the atoms is not cooperative but rather given by
independent thermally activated hops of individual atoms between the pockets.
By determining the probability that an atom returns to a given starting site,
we show that such events are not important for the dynamics of this system.
