  We are interested in comparing properties of symplectic mapping class groups
of symplectic manifolds of dimension four or higher with properties of
classical mapping class groups of surfaces. For $n \geq 2$, consider a
configuration of Lagrangian $S^n$s in a Weinstein domain $M^{2n}$. If it is
analogous, in some sense that we make precise, to a configuration of exact
Lagrangian $S^1$s on a surface $\Sigma$, we show that any relation between Dehn
twists in the $S^n$s must also hold between the $S^1$s. Such analogous pairs of
configurations include plumbings of $T^\ast S^1$s and $T^\ast S^n$s with the
same plumbing graph, and vanishing cycles for a two-variable singularity and
for its stabilisation. We give a number of corollaries for subgroups of
symplectic mapping class groups.
