Reversible neural inactivation reveals hippocampal participation in several memory processes

Studies of patients and animals with brain lesions have implicated the hipp ocampal formation in spatial, declarative/relational and episodic types of memory. These and other types of memory consist of a series of interdepende nt but potentially dissociable memory processes-encoding, storage, consolid ation and retrieval. To identify whether hippocampal activity contributes t o these processes independently, we used a novel method of inactivating syn aptic transmission using a water-soluble antagonist of AM PA/kainate glutam ate receptors. Once calibrated using electrophysiological and two-deoxygluc ose techniques in vivo, drug or vehicle was infused chronically or acutely into the dorsal hippocampus of rats at appropriate times during or after tr aining in a water maze. Our findings indicate that hippocampal neural activ ity is necessary for both encoding and retrieval of spatial memory and for either trace consolidation or long-term storage.