Biorhythmic state dependency and the efficacy of a reminder treatment for recovery from ECS-induced amnesia in the rat



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Current evidence of fluctuating levels of retention performance associated with different phases of a 12-hour internal biorhythm suggests that the effect of any memory related treatment may also vary, depending upon the time selected for administration. Using an ECS-induced experimental amnesia paradigm, a series of experiments were conducted to investigate the amount of recovery from amnesia resulting from the administration of reminder treatments at various post-training intervals associated with different phases of the internal biorhythm. The results of Experiment 1 demonstrated evidence of biorhythmic oscillations in retention performance for a one-trial, passive-avoidance step-down task. In Experiment 2, subjects were trained on the step-down task and rendered amnesic with ECS. Kinesthetic reminders, given at various intervals after training, failed to show any differential effects when retention was measured immediately after the reminder treatment, irrespective of when the reminder and retention test occurred. For Experiment 3, kinesthetic reminders, supplied at different intervals prior to a 24-hour retention test and again during the test, produced some recovery when both reminders were presented during equivalent phases of the biorhythmic function, indicating a summation of effects. A passive-avoidance step-through task was used in Experiment 4 and foot shock reminders were administered at different intervals post-acquisition. Maximum levels of recovery from amnesia were observed immediately, 12 or 24 hours after training, when retention was measured 15 minutes after the reminder treatments. For Experiment 5, all subjects displayed some recovery on a 24-hour retention test following a reminder foot shock, but only those subjects reminded at 6 hours displayed near maximum levels of recovery. The results of these experiments suggest that the time selected for administration of various reminder treatments partially determines the amount of recovery from amnesia evidenced on a retention test. The use of reminders in conjunction with the presence of biorhythmically determined information resulted in complete recovery when retention was measured shortly after the treatment. On a 24-hour deficit, evidence of near complete recovery arising from a 6 hour reminder represents somewhat of a paradox. A competition/interference gradient associated with the presence or absence of biorhythmic information was proposed to account for the dilemma.