Morris water maze
Encyclopedia
The Morris water navigation task is a behavioral procedure widely used in behavioral neuroscience
to study spatial learning and memory
. It was developed by neuroscientist Richard G. Morris in 1981, who used it to show that lesions of the hippocampus
impaired spatial learning.
In the typical paradigm, a rat or mouse is placed into a small pool of water—back-end first to avoid stress, and facing the pool-side to avoid bias—which contains an escape platform hidden a few millimeters below the water surface. Visual cues, such as colored shapes, are placed around the pool in plain sight of the animal. The pool is usually 1.2 to 1.8 meter in diameter and 60 centimeters deep. The pool can also be half-filled with water to 30 centimeters in depth. A sidewall above the waterline prevents the rat from being distracted by laboratory activity. When released, the rat swims around the pool in search of an exit while various parameters are recorded, including the time spent in each quadrant of the pool, the time taken to reach the platform (latency
), and total distance traveled. The rat's escape from the water reinforces its desire to quickly find the platform, and on subsequent trials (with the platform in the same position) the rat is able to locate the platform more rapidly. This improvement in performance occurs because the rat has learned where the hidden platform is located relative to the conspicuous visual cues. After enough practice, a capable rat can swim directly from any release point to the platform.
blocker APV
perform poorly in the Morris water maze, suggesting that NMDA receptors play a role in learning. And since long-term potentiation
(LTP) also requires NMDA receptors, spatial learning may require LTP.
Liang et al. reported in 1994 that acquisition requires both NMDA
and AMPA receptor
s, consolidation requires NMDA receptors.
Initial studies in the early eighties suggested that laboratory mice seemed to have a tendency to float, perhaps leading to their perceived uncooperativeness in the water maze. Thus, it was suggested that mice did not actually aim to find the platform, but simply waited until the technician rescued them, though watermazes have now been utilized extensively in thousands of published experiments with transgenic and knock out mice. The key with using mice is to use procedures that minimize stress (e.g., handling the mice for a few minutes every day before the start of training can reduce stress during training and improve performance in this task). Also, it is important to avoid using mouse strains that are blind or that lack spatial navigation (e.g. have unknown genetic or/and neuroanatomical lesions that disrupt hippocampal function).
, which is the time it takes to find the platform. However, rats and mice can cheat. They might develop search techniques that do not rely on spatial information, still getting to the platform relatively quickly. There are several analyzes that can tease out true spatial learning, many of which use probe trials during training: the escape platform is removed and the mice or rats are allowed to search for it for a fixed time (often 60 seconds). Analysis of the probe trial is made easier with a video tracker that traces the swimming patterns of the animals while searching for the platform. Commercial systems come with a suite of analysis features to extract measures such as time and path in quadrants, near platform, in any specified area. The Gallagher measure looks for average distance to platform. The Whishaw corridor test measures time and path in a strip from swim-start to platform.
Behavioral neuroscience
Behavioral neuroscience, also known as biological psychology, biopsychology, or psychobiology is the application of the principles of biology , to the study of physiological, genetic, and developmental mechanisms of behavior in human and non-human animals...
to study spatial learning and memory
Spatial memory
In cognitive psychology and neuroscience, spatial memory is the part of memory responsible for recording information about one's environment and its spatial orientation. For example, a person's spatial memory is required in order to navigate around a familiar city, just as a rat's spatial memory is...
. It was developed by neuroscientist Richard G. Morris in 1981, who used it to show that lesions of the hippocampus
Hippocampus
The hippocampus is a major component of the brains of humans and other vertebrates. It belongs to the limbic system and plays important roles in the consolidation of information from short-term memory to long-term memory and spatial navigation. Humans and other mammals have two hippocampi, one in...
impaired spatial learning.
Overview
In the typical paradigm, a rat or mouse is placed into a small pool of water—back-end first to avoid stress, and facing the pool-side to avoid bias—which contains an escape platform hidden a few millimeters below the water surface. Visual cues, such as colored shapes, are placed around the pool in plain sight of the animal. The pool is usually 1.2 to 1.8 meter in diameter and 60 centimeters deep. The pool can also be half-filled with water to 30 centimeters in depth. A sidewall above the waterline prevents the rat from being distracted by laboratory activity. When released, the rat swims around the pool in search of an exit while various parameters are recorded, including the time spent in each quadrant of the pool, the time taken to reach the platform (latency
Latency (engineering)
Latency is a measure of time delay experienced in a system, the precise definition of which depends on the system and the time being measured. Latencies may have different meaning in different contexts.-Packet-switched networks:...
), and total distance traveled. The rat's escape from the water reinforces its desire to quickly find the platform, and on subsequent trials (with the platform in the same position) the rat is able to locate the platform more rapidly. This improvement in performance occurs because the rat has learned where the hidden platform is located relative to the conspicuous visual cues. After enough practice, a capable rat can swim directly from any release point to the platform.
Pharmacological manipulation
Various drugs can be applied to test subjects before, during, or after maze training, which can reveal information about physical ability. For example rats treated with the NMDA receptorNMDA receptor
The NMDA receptor , a glutamate receptor, is the predominant molecular device for controlling synaptic plasticity and memory function....
blocker APV
APV (NMDAR antagonist)
AP5 or APV is a selective NMDA receptor antagonist that competitively inhibits the ligand binding site of NMDA receptors....
perform poorly in the Morris water maze, suggesting that NMDA receptors play a role in learning. And since long-term potentiation
Long-term potentiation
In neuroscience, long-term potentiation is a long-lasting enhancement in signal transmission between two neurons that results from stimulating them synchronously. It is one of several phenomena underlying synaptic plasticity, the ability of chemical synapses to change their strength...
(LTP) also requires NMDA receptors, spatial learning may require LTP.
Liang et al. reported in 1994 that acquisition requires both NMDA
NMDA receptor
The NMDA receptor , a glutamate receptor, is the predominant molecular device for controlling synaptic plasticity and memory function....
and AMPA receptor
AMPA receptor
The α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor is a non-NMDA-type ionotropic transmembrane receptor for glutamate that mediates fast synaptic transmission in the central nervous system . Its name is derived from its ability to be activated by the artificial glutamate analog AMPA...
s, consolidation requires NMDA receptors.
Comparison to conventional mazes
The Morris water navigation task has some advantages over conventional mazes such as the T-maze. For instance, there are no local cues such as scent traces and there is no fixed escape-formula; the rat makes good progress in the trials because it wants to escape. Rats (but not mice) can be considered to be natural swimmers – they are not distressed but they do want to find the platform.Initial studies in the early eighties suggested that laboratory mice seemed to have a tendency to float, perhaps leading to their perceived uncooperativeness in the water maze. Thus, it was suggested that mice did not actually aim to find the platform, but simply waited until the technician rescued them, though watermazes have now been utilized extensively in thousands of published experiments with transgenic and knock out mice. The key with using mice is to use procedures that minimize stress (e.g., handling the mice for a few minutes every day before the start of training can reduce stress during training and improve performance in this task). Also, it is important to avoid using mouse strains that are blind or that lack spatial navigation (e.g. have unknown genetic or/and neuroanatomical lesions that disrupt hippocampal function).
Water maze analysis
The earliest and classic measure of learning is latencyLatency (engineering)
Latency is a measure of time delay experienced in a system, the precise definition of which depends on the system and the time being measured. Latencies may have different meaning in different contexts.-Packet-switched networks:...
, which is the time it takes to find the platform. However, rats and mice can cheat. They might develop search techniques that do not rely on spatial information, still getting to the platform relatively quickly. There are several analyzes that can tease out true spatial learning, many of which use probe trials during training: the escape platform is removed and the mice or rats are allowed to search for it for a fixed time (often 60 seconds). Analysis of the probe trial is made easier with a video tracker that traces the swimming patterns of the animals while searching for the platform. Commercial systems come with a suite of analysis features to extract measures such as time and path in quadrants, near platform, in any specified area. The Gallagher measure looks for average distance to platform. The Whishaw corridor test measures time and path in a strip from swim-start to platform.