Unilateral hippocampal blockade reveals that one hippocampus is sufficient for learning a passive avoidance task.

Understanding hippocampal participation in memory processes is one of the goals in neuroscience research. By blocking the hippocampus unilaterally in Wistar rats, we assessed the contribution of this brain structure to memory in a passive avoidance task. Subjects were distributed into four groups. Group 1 received tetrodotoxin (TTX) in the right hippocampus during acquisition and retrieval phases. Group 2 had the same procedure as group 1, except that the contralateral hippocampus was blocked during retrieval. Subjects from group 3 acquired the task with saline (both hippocampi intact) and retrieved with the right hippocampus inactivated. Finally, group 4 received TTX unilaterally 2 min after acquisition to determine the hippocampal role in consolidation. Results showed that group 2 was impaired, compared with the other groups, during retrieval. These findings reveal that the hippocampal contribution to this task differs from that in other tasks considered to be hippocampus dependent.