area as the turning point of the minimal surface approaches the horizon.\
A second important aspect of the entanglement entropy we are interested in concerns the case of a spatial region $A$ in the boundary made by two disjoint regions, i.e. $A= A_1 \cup A_2$ with $ A_1 \cap A_2 = \emptyset$. In this case the natural quantity to consider is the mutual information $M_A \equiv S_{A_1}+S_{A_2}-S_{A_1 \cup A_2}$ because it is UV finite. For some spin chains and two dimensional conformal field theories interesting results have been obtained [@Caraglio:2008pk; @Furukawa:2008uk; @Calabrese:2009ez; @Alba:2009ek; @Fagotti:2010yr; @Casini:2005rm; @Casini:2008wt; @Casini:2009vk]. The models considered in these papers have small central charges (order of the unity).\
In the context of the holographic correspondence, the case of disjoint regions has been addressed in [@Ryu:2006bv; @Ryu:2006ef; @Hirata:2006jx; @Headrick:2007km; @Hubeny:2007re; @Headrick:2010zt]. An interesting feature of the holographic entanglement entropy is the transition of the mutual information from zero value to a positive value (the mutual information cannot be negative, as a consequence a strong subadditivity inequality) [@Hirata:2006jx; @Headrick:2010zt]. This transition should be a large $c$ effect, which is the regime where the holographic prescription works, since there no signal of it e.g. for the compactified boson [@Furukawa:2008uk; @Calabrese:2009ez], 