Morris water maze: a versatile and pertinent tool for assessing spatial learning and memory

Abstract

Since its development about 40 years ago (1981-2021), Morris water maze has turned into a very popular tool for assessing spatial learning and memory. Its many advantages have ensured its pertinence to date. These include its effectiveness in evaluating hippocampal-dependent learning and memory, exemption from motivational differences across diverse experimental manipulations, reliability in various cross-species studies, and adaptability to many experimental conditions with various test protocols. Nonetheless, throughout its establishment, several experimental and analysis loopholes have galvanized researchers to assess ways in which it could be improved and adapted to fill this gap. Therefore, in this review, we briefly summarize these developments since the early years of its establishment through to the most recent advancements in computerized analysis, offering more comprehensive analysis paradigms. In addition, we discuss the adaptability of the Morris water maze across different test versions and analysis paradigms, providing suggestions with regard to the best paradigms for particular experimental conditions. Hence, the proper selection of the experimental protocols, analysis paradigms, and consideration of the assay's limitations should be carefully considered. Given that appropriate measures are taken, with various adaptations made, the Morris water maze will likely remain a relevant tool to assess the mechanisms of spatial learning and memory.

Keywords: Morris water maze; hippocampal-dependent learning and memory; spatial learning and memory.

Fig. 1.

The anatomy of the rodent hippocampus. Place cells (complex spiking pyramidal cells) have been found in the CA3 and CA1 of the hippocampus. Image of the whole brain with the coronal sectioning of the hippocampal structure was created from an open access software (Allen Brain Atlas − Brain Explorer^® 2). Pentagonal cells represent granular neurons of dentate gyrus, whereas triangular cells represent pyramidal neurons of CA3 and CA1.

Fig. 2.

The Barnes Maze. Animal is placed at the centre of the maze platform. Ample visual cues are placed in the test room as spatial guides for navigational purposes. Animal may employ various search strategies to locate the target hole, as illustrated in the figure.

Fig. 3.

The discovery of the hippocampal place cells led to the development of Radial Arm Maze (RAM) and Morris Water Maze (MWM). Since then, MWM has been undergoing varieties of improvements and adaptations, including in the computational neuroscience, human and animal studies.

Fig. 4.

(A) Four equally sized quadrants in the MWM pool. (B) The quadrants further divided with peripheral ring (each quadrant comprises internal and external area, giving rise to eight sub-quadrants in total). (C) Peripheral ring shaded in pink for thigmotaxis evaluation. N=North; E=East; S=South; W=West.

Fig. 5.

Illustrated animal swimming paths and predicted results for normal versus sedated animals during the 60 s-probe trial with different analysis parameters: (A) time spent; (B) distance in the target quadrant. Target quadrant shaded in pink.