Inactivating one hippocampus impairs avoidance of a stable room-defined place during dissociation of arena cues from room cues by rotation of the arena

Unilateral intrahippocampal injections of tetrodotoxin were used to tempora rily inactivate one hippocampus during specific phases of training in an ac tive allothetic place avoidance task. The rat was required to use landmarks in the room to avoid a room-defined sector of a slowly rotating circular a rena. The continuous rotation dissociated room cues from arena cues and mov ed the arena surface through a part of the room in which foot-shock was del ivered. The rat had to move away from the shock zone to prevent being trans ported there by the rotation. Unilateral hippocampal inactivations profound ly impaired acquisition and retrieval of the allothetic place avoidance. Po sttraining unilateral hippocampal inactivation also impaired performance in subsequent sessions. This allothetic place avoidance task seems more sensi tive to hippocampal disruption than the standard water maze task because th e same unilateral hippocampal inactivation does not impair performance of t he variable-start, fixed hidden goal task after procedural training. The re sults suggest that the hippocampus not only encodes allothetic relationship s amongst landmarks, it also organizes perceived allothetic stimuli into sy stems of mutually stable coordinates. The latter function apparently requir es greater hippocampal integrity.