Some possible neurological applications of applied potential tomography

The applicability of applied potential tomography (APT) to imaging neuronal discharge and spreading depression in the brain has been assessed with single channel impedance measurements. Stimulation of frog sciatic nerve, rat cortex and human subjects produced no changes in impedance measured at 50 kHz greater than 0.02%, which suggests that APT systems currently in use could not image neuronal discharge in practice. Larger changes in impedance of about 40% during spreading depression could be reproducibly measured on rat cortex, and could be simulated by a mathematical model. The signal was attenuated but detectable when measured on the dura and outside the skull. Spreading depression could provide a useful model for the development of APT in the brain, which, if achievable, could lead to applications of clinical value in neurology and neurosurgery.