Intracranial injection of Ca**2** plus or Mg**2** plus left bracket 20 mu 1, 40 mM right bracket in chronically implanted neonatal chicks resulted in an almost immediate synchronization of the hyperstriatal EEG, accompanied by behavioral depression. During successive testing days, the animals appeared to recover behaviorally but never showed any sustained EEG arousal. By contrast, animals treated with sodium chloride recovered completely within the first hour after the injection. The chick forebrain, being so highly sensitive to small perturbations of the extracellular concentrations of either divalent cations, was therefore chosen for investigating, in vitro, the possible interactions between extracellular weak voltage gradients, induced by vhf radiations, and ionic movements in cerebral tissue. In the present experiment, **4**5Ca**2** plus fluxes from irradiated brains are compared at various frequencies of amplitude modulation of the carrier wave.