Preliminary observations with a technique for measuring current spread in the rat brain

Intracranial spread of current from monopolar and bipolar electrode configurations was evaluated by using a motor effect of VII nerve stimulation. A tripolar electrode was lowered through the medulla toward the nerve in 1 mm steps; the currents necessary to produce threshold levels of sustained vibrissae vibration with monopolar and bipolar combinations of tips were determined at each step. Bipolar stimulation had a steep gradient and its effects were largely confined to a region within 2 mm of the minimum threshold point. Monopolar stimulation had a broader gradient and spread further. This technique appears promising for quantitative evaluation of ICS characteristics.