Electrical Impedance as a Locating Method in Human Stereotactic Surgery

During stereotactic surgery, electrical impedance was measured by means of a roving electrode technique with a sine wave current of 10 kc. Impedance showed a characteristic decrease when the electrode was passing through the thalamus and consequently the impedance profile corresponding to the thalamic area exhibited the characteristic shape of a ‘frying pan’. By observing the impedance, it is possible to differentiate the thalamic gray matter from the surrounding structures with some accuracy.