Evidence for extrahippocampal involvement in place learning and hippocampal involvement in path integration

A Behavioral Analysis of the Spatial Learning Deficit Induced by the NMDA Receptor Antagonist MK-801 (Dizocilpine) in the Rat

“…This indicates that MK-801-treated rats can utilize visual cues, although their cue-mediated navigation abilities are impaired. Importantly, unlike rats with gross lesions of the hippocampus they did not return to the previous location of the platform after it had been moved to a new location (Morris et al 1982;Whishaw et al 1995;Whishaw and Jarrad 1996;Whishaw and Tomie 1997). In contrast, the 0.05 mg/kg group and the control group were slightly impaired in their acquisition performance on the first trials after the platform was moved to the new location indicating that these two groups used a spatial search strategy.…”

“…This approach differs from the frequently used visible platform version in which the animal has to climb onto the platform protruding from the water Cain et al 1997;Saucier et al 1996;Whishaw et al 1995;Whishaw and Jarrad 1996;Whishaw and Tomie 1997). In the present study, retention was always tested The behavioral tests used in these studies discriminate unspecific drug effects from those on learning and memory.…”

The hippocampal debate: are we asking the right questions?

“…This was quickly taken as proof of O'Keefe and Nadel's cogniti6e map hypothesis [126]. But, since those initial studies, it has been shown that animals with a variety of hippocampal impairments could, in fact learn the hidden-platform water maze if they were given appropriate training [41,49,[232][233][234][235] The issue, of course, is that the water maze is not solved by a hippocampus in isolation, it is solved by a navigational system involving many structures beyond the hippocampus. These non-hippocampal structures may be able to solve the water maze under specific training paradigms.…”

“…In particular, as predicted by O'Keefe and Nadel [150], non-hippocampal navigation systems require immediate sensory cues off of which they can trigger the response (for example, hippocampal animals can beacon to a visible cue [49]). When immediate cues are not available, non-hippocampal navigation systems can learn to trigger off more complex cues if given sufficient training and if the complex cues are sufficiently different (for example, if they are first overtrained with a visible platform [234]). …”

“…Hippocampally-impaired animals can find the hidden platform if they are always started from the same location [49,235], if a cue is available toward which they can swim [49], if a cue is available from which they can generate a heading vector [162], or if they are overtrained first with a visible platform [234]. One of the best examples of a specific training paradigm that allows animals to show place learning with hippocampal lesions is training the animal with a shrinking platform [41].…”