1. A system for applying electrical stimulation to a cortical stimulation site proximate to the surface of the cortex of a patient, the system comprising: a stimulus unit having a pulse system including a first terminal that can be biased at a first polarity and a second terminal that can be biased at a second polarity; a surface electrode assembly having a support member configured to be implanted in the patient at the stimulation site, a plurality of surface contacts carried by the support member, and a first lead attached to the surface contacts, wherein the first lead is configured to be attached to the first terminal of the pulse system for biasing the surface contacts at the first polarity; and a return contact detached from the surface electrode assembly and configured to be coupled to the second terminal of the pulse system to be biased at the second polarity, wherein the return contact is configured to be spaced apart from the stimulation site in operation.