I do not believe a rat with a removed hippocampus can navigate a morris water maze.They certainly can not learn to navigate it, but it looks like retention is damaged as well: Memory generally falls into three categories for humans anyway, verbal visual and spatial (sometimes visual and spatial are combined into visuospatial). Memories are not necessarily stored in equal parts through out the brain either, it varies widely depending on the individual and the type of memory. If you look at a picture and encode it to long term memory, you will have the vast majority of that memory encoded visually. If you read an abstract paper about something technical, you will encode the vast majority of that paper verbally. It is simply inefficient to try and recall a picture with verbal memory, just as it is essentially impossible to visually recall an abstract system without a whole lot of support from verbal memory. There are many ways to remember and process information, although some strategies are far superior to others. A human without a hippocampus cannot form spatial memories, so every time they try to solve such a maze they are starting with essentially zero knowledge of the path they have taken in previous iterations of trying to solve the maze, and zero ability to orient themselves. However, they can remember verbal information, and depending on the sort of maze they may be able to remember a series of turns and encode the solution to the maze as 'left, down, right, up, left, left' or something. Not the best strategy for solving the maze but it could work I imagine. As far as a rat goes though, I think they are totally fucked on solving a maze if their hippocampus is destroyed.