Cognitive Function Assays

Water Maze

The water maze can assess spatial learning and memory. In the typical paradigm, a rat or mouse is placed into a pool of water, which contains an escape platform hidden a few millimeters below the water surface. Visual cues, such as high contrast shapes, are placed around the pool in plain sight of the animal. Several measures are analyzed by an automated tracking system, including the escape latency (the time taken to reach the platform) the time spent in each quadrant of the pool, total distance traveled and swim speed.

Object Recognition and Object Placement

These tests of recognition and spatial memory are based on rodents’ robust preferential exploration of novel objects. The mouse is placed in an opaque arena, which contains two identical objects (such as plastic, glass or ceramic items) after which the animal is returned to the home cage. After a suitable retention interval, the subject is returned to the arena in which one of the familiar objects has been replaced with a novel object. Normal animals consistently explore the novel object in preference to the familiar one. A preference score (time exploring the novel object/total object exploration) of 50% indicates chance performance.

Spatial memory and pattern recognition can also be assessed using a variation of this protocol. In the object placement task, the animal is first exposed to two identical objects, as before, but in the test trial one of the objects has been displaced in space. Normal rodents preferentially explore the displaced object.

These tasks do not require food or water deprivation and are very similar to tests of visuospatial working memory conducted in humans. These can be repeated in the same subjects and are thus useful for longitudinal and/or rescue studies (1)

Conditioned Taste Aversion

This one-trial form of associate memory is based on rodents’ reliable aversion to flavors that have previously been paired with sickness. In conditioned taste aversion, the subject is exposed to flavored water for several days. Then, one of the flavors of water is paired with injection (LiCl) that causes nausea. The subject is later given a choice between the paired and non-paired flavor (2).

Spontaneous Alternation

When exposed to a Y-shaped arena, rodents naturally alternate their exploration of the three arms. Animals with navigational, spatial or attention deficits tend to re-visit arms they have just entered. Total activity can be measured by the number of arms entered whereas correct spontaneous alternation is analyzed by tracking software as the pattern of arm entries (3).

Delayed Alternation

Subjects are first placed in the start arm of a Y or T Maze. Upon leaving the start arm, subjects choose between entering either the left or the right goal arm. With repeated trials, the animals should show less of a tendency to enter a previously visited arm. The percentage of correct choices in total, per each trial and per block of 5 trials is recorded. The delayed alternation can be either spontaneous (i.e. animals freely allowed to choose which arm to enter) or forced (i.e. one arm is block off during exploration and the animal must chose the alternate arm during test). (4, 5)

Labyrinth Maze

Spatial learning and memory can be assessed in a labyrinth maze, using palatable food/drink or social contact as a reward. Learning is assessed as decreased time to reach the goal in successive trials, and memory as the maintenance of established levels after suitable retention intervals (6).

Social Discrimination

Social discrimination memory utilizes the natural tendency of rodents to prefer novel conspecifics rather than familiar ones. This first trial of the test is actually a social preference assay, and is also useful for measuring the social withdrawal relevant to depression, anxiety and deficits in social interaction typical of autism spectrum disorders. In the second trial, subjects are exposed to a novel or a familiar conspecific. When memory systems are intact, rodents preferentially explore the novel stimulus animal. As this test is based on olfaction, it is useful especially when animals have deficits in the visual or auditory system (7).

Marble Burying

The marble burying test is a useful model of neophobia (8), anxiety (8-14) and obsessive-compulsive behavior (15-18). It has also been proposed that the test may have predictive validity for the screening of novel antidepressants (19-22), anxiolytics (22, 23) and antipsychotics (24-26). It is also a measure of the general health and well being of the animals and may be relevant to behavioral perseverance.

Conditioned Fear

Fear conditioning assesses the freezing response that takes place following pairing of an unconditioned stimulus (US), such as foot shock, with a conditioned stimulus(CS), such as a particular context or a cue (e.g. light or sound) (27).

References

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