Fitting a brain neurostimulator electrode array comprises positioning at least a first electrode in a desired target structure in a first cerebral hemisphere, and positioning at least a second electrode in a corresponding target structure in a contralateral cerebral hemisphere. Electrical stimuli are applied from the first electrode to the desired target structure. Neural responses observed at the second electrode in response to the electrical stimuli are recorded. The fitting of at least one of the first electrode and second electrode is assessed by reference to the recorded neural responses.