Let $(R,m)$ be a complete regular local ring. Let $U=\operatorname{Spec}R-\{m\}$ be the complementary open set of a closed point in $\operatorname{Spec}R$, and let $I$ be the ideal of $R$. Then it is stated that $\operatorname{H}^0(\hat{U},\mathcal{O}_\hat{U})=\varprojlim_{x\in U\cap V(I)}\mathcal{O}_{\hat{U},x}$, where $\hat{U}$ is the completion of $U$ along $V(I)\cap U$.
Why $\operatorname{H}^0(\hat{U},\mathcal{O}_\hat{U})$ can be written as the inverse limit as above? What is the arrow in this inverse system? I know $\mathcal{O}_{\hat{U}}$ can be expressed as $\varprojlim \mathcal{O}_U/\mathcal{I}^n$ where $\mathcal{I}$ is the sheaf of ideals.