Commuting maps on the Heisenberg algebra

Given a ring $R$ with center $Z(R)$, we say a linear map $f:R\to R$ is commuting if $[f(x),x]=0$ for all $x\in R$. Such a map has a standard form if there exists $\lambda \in R$ and additive $\mu :R\to Z(R)$ such that $f(x)=\lambda x+\mu (x)$ for all $x\in R$. We characterize the linear commuting maps over the $n\times n$ Heisenberg algebra, showing that such maps need not be of the standard form.