  We study the effect of lesions on our four-electrode measurements of the
ionic conductivity of (1 cm3) samples of human brain excised from patients
undergoing pediatric epilepsy surgery. For most (about 94 %) samples the
low-frequency ionic conductivity rises upon increasing the applied frequency.
We attributed this behavior to the long-range (0.4 mm) diffusion of solvated
sodium cations before encountering impenetrable blockages such as cell
membranes, blood vessels and cell walls. By contrast, the low-frequency ionic
conductivity of some (6 %) brain tissue samples falls with increasing applied
frequency. We attribute this unusual frequency-dependence to the electric-field
induced liberation of sodium cations from traps introduced by the unusually
severe pathology observed in samples from these patients. Thus, the anomalous
frequency-dependence of the ionic conductivity indicates trap-producing brain
lesions.
