A method and a control system (20) are provided for determining a relation between stimulation settings for a brain stimulation probe (10) and a corresponding V-field. The brain stimulation probe (10) comprises multiple stimulation electrodes (11). The V-field is an electrical field in brain tissue surrounding the stimulation electrodes (11). The method comprises sequentially applying a test current to n stimulation electrodes (11), n being a number between 2 and the number of stimulation electrodes (11) of the brain stimulation probe (10), for each test current at one of the n stimulation electrodes (11), measuring a resulting excitation voltage at m stimulation electrodes, m being a number between 2 and the number of stimulation electrodes (11) of the brain stimulation probe (10), from the stimulation settings and the measured excitation voltages, deriving an (m*{acute over (η)}) coupling matrix, an element (q, p) in the coupling matrix reflecting an amount of electrical impedance between two of the stimulation electrodes (11), and using the coupling matrix for determining the relation between the stimulation settings and the corresponding V-field.