Retrograde amnesia gradients by subconvulsive and high convulsive transcranial currents in chicks.

Either a subconvulsive or a high convulsive current was delivered transcranially at various intervals after a learning trial to independent groups of newly hatched chicks. The one-trial learning involves suppression of the chicks' predilection to peck at a small shiny bead. The effect of current on retention was measured one day later. Results indicate a current-sensitive memory consolidation period of about 30 seconds that cannot be appreciably prolonged by a tenfold increase in current intensity and a simultaneous twofold increase in current duration. On the other hand, at comparable trial-to-current intervals within this brief consolidation period, more retention deficit was caused by the higher current. Beyond this critical period, both currents still effected some retention deficit, but it did not seem to vary with the trial-to-current interval from one minute to 24 hours. Overt muscular convulsion was unnecessary for the retrograde amnesia effect. The subconvulsive current may be a more pure agent for consolidation studies because the high, convulsive current may affect test performance in ways other than disrupting the consolidation processes.