Functional dissociation of acute and persistent cognitive deficits accompanying amygdala-kindled seizures

The effects of amygdala-kindled seizures on cognitive function were examined using long-delay flavor-aversion and passive-avoidance conditioning paradigms in rats. Experiments were conducted to compare the functional consequences of unilateral and bilateral kindled seizures (transient deficits) with those due to a kindling history only (persistent deficits). Animals with a history of unilateral or bilateral kindling demonstrated flavor-aversion conditioning that varied inversely with the delay separating saccharin (CS) and lithium (US). Unilateral stimulation during the CS-US interval produced an attenuation of flavor-aversion conditioning that was independent of delay value; bilateral stimulation eliminated conditioning all together. The effects of kindling and kindled seizures on passive-avoidance conditioning were functionally identical. Animals with a history of unilateral kindling demonstrated strong evidence of conditioning with no effect of posttraining seizures. In contrast, animals with a history of bilateral kindling were impaired in a passive-avoidance task. The impairment was evident in the presence or absence of seizure induction during training. Electrographic and behavioral indices of epileptiform activity produced by unilateral and bilateral stimulation failed to reveal any differences in seizure duration or severity. The results support the conclusion that cognitive disruption by amygdala-kindled seizures is task-dependent, does not show a temporal dependence, and cannot be explained on the basis of electrographic or behavioral measures of seizure severity alone.