Sustained dorsal hippocampal activity is not obligatory for either the maintenance or retrieval of long-term spatial memory.

Memories are initially stored in a labile state and are subject to modification by a variety of treatments, including disruption of hippocampal function. We infused a sodium channel blocker (or CNQX) to inactivate the rat dorsal hippocampus reversibly for 1 week following training on a task of spatial memory (the water maze). Previous work with conventional lesions has established that the dorsal hippocampus is essential for both the acquisition and expression of memory in this task. The question in the present study was whether chronic disruption of neuronal activity in the dorsal hippocampus after training would abolish memory or whether memory would survive extended disruption of hippocampal activity. As expected from earlier work, we found that performance was impaired during the infusion period. The critical test occurred 1 week after the lesion was reversed. We found that retention of the water maze recovered to control levels. Accordingly, sustained hippocampal activity following training is not obligatory for either the maintenance of long-term spatial memory or its subsequent retrieval.