Atomistic calculations of the ½〈1 1 0〉 screw dislocation core structure in MgO have been carried out showing the influence of high pressure (up to 100 GPa) on the core spreading. Calculations rely on a periodic arrangement of dislocation quadrupoles. Comparison between first principles and pairwise potential simulations show a remarkable agreement. Our results confirm that the dislocation core evolves from a spreading in {1 1 0} (at low pressure) to a narrower configuration spread in {1 0 0} as pressure increases. The periodic dipole method enables us also to record the pressure induced core energy variations.