Abstract
The Morris water maze represents the de-facto standard for testing hippocampal function in laboratory rodents. In the field of adult hippocampal neurogenesis, however, using this paradigm to assess the functional relevance of the new neurons yielded surprisingly inconsistent results. While some authors found aspects of water maze performance to be linked to adult neurogenesis, others obtained different results or could not demonstrate any effect of manipulating adult neurogenesis. In this review we discuss evidence that the large diversity of protocols and setups used is an important aspect in interpreting the differences in the results that have been obtained. Even simple parameters such as pool size, number, and configuration of visual landmarks, or number of trials can become highly relevant for getting the new neurons involved at all. Sets of parameters are often chosen with implicit or explicit concepts in mind and these might lead to different views on the function of adult-generated neurons. We propose that the classical parameters usually used to measure spatial learning performance in the water maze might not be particularly well-suited to sensitively and specifically detect the supposedly highly specific functional changes elicited by the experimental modulation of adult hippocampal neurogenesis. As adult neurogenesis is supposed to affect specific aspects of information processing only in the hippocampus, any claim for a functional relevance of the new neurons has to be based on hippocampus-specific parameters. We also placed a special emphasis on the fact that the dentate gyrus (DG) facilitates the differentiation between contexts as opposed to just differentiating places. In conclusion, while the Morris water maze has proven to be one of the most effective testing paradigms to assess hippocampus-dependent spatial learning, new and more specific questions ask for new parameters. Therefore, the full potential of the water maze task remains to be tapped.
Highlights
Adult hippocampal neurogenesis deserves much of its attention due to the fact that it adds new functional neurons to a brain structure that is of particular importance for learning and memory processes (Kempermann, 2012)
In conclusion, the variety of setups, protocols, and parameters used to address the functional contribution of adult neurogenesis to spatial learning in the water maze task do not always reflect the specific prerequisites presumed to be necessary to get the new neurons involved
The significant mismatch between the inconsistent results from numerous water maze experiments and the rather homogenous theoretical concepts proposed for the functional relevance of adult neurogenesis is taking the classical ways to set up and analyze a water maze experiment into question
Summary
Adult hippocampal neurogenesis deserves much of its attention due to the fact that it adds new functional neurons to a brain structure that is of particular importance for learning and memory processes (Kempermann, 2012). Since a large number of studies has shown that many aspects of spatial learning depend on an intact and fully functional hippocampus and given that for at least some species the generation of new hippocampal neurons in the adult brain appears to provide an advantage in evolution (Kempermann, 2012), it is somewhat surprising that neither a significant reduction nor an increase of adult neurogenesis were consistently found to result in a strong and specific phenotype in the water maze task.
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
