Assessments of Cognitive Function Following Traumatic Brain Injury - Animal Models of Acute Neurological Injuries: Injury and Mechanistic Assessments - page 216

to diffi culties with executive function, attention and information
processing speed, all of which require some degree of working
memory ( 17 ).

The MWM apparatus is a large circular tank (180 cm diameter by
45 cm high) fi lled with water to a depth of 30 cm. MWM tanks are
commercially available. The water is often made opaque by addi-
tion of approximately 500 ml of nontoxic white latex paint. The
water temperature should be maintained between 23 and 26°C
with a heater. A hidden escape platform (10 cm in diameter, located
2 cm below the water surface) is placed about 45 cm from the
outside of the maze wall. Several extra-maze visual cues (e.g., pictures,
shapes, or fl ag) are placed on the walls around the water maze and
remain in a constant position throughout tests. It is very important
that no intra-maze cues exist. The animal's movements within
the MWM are recorded and analyzed with a video camera and a
Windows-compatible software package (e.g., Videomax, Columbus
Instruments, OH).

2.1.1. Morris Water Maze
Apparatus

In the spatial navigation task of the MWM, animals are given four
trials per day over several consecutive days (4-5 days). It is impor-
tant that animals are suffi ciently handled before testing begins. On
each day of MWM testing, rats are placed in a pool by hand in one
of four locations (North, South, East, and West) facing the wall of
the tank. Each animal must start a trial at each of the four loca-
tions on each day. The order of starting locations is randomized
each day to minimize practice effects. The goal platform is placed
45 cm from the outside wall in the southeast quadrant and remains
constant throughout testing. Rats are given a maximum of 120 s
to fi nd the goal. After this time, rats are placed on the goal and
held there for 30 s. The rats are then removed from the maze and
placed in an incubator until the next trial. Average latencies to
reach the goal platform on each day of testing are the predomi-
nant outcome measure, but distance and swim speed can also be
calculated. Probe trials can be used to test for memory retention
following completion of the acquisition training. The probe trial
is performed no less than 6 h after completion of the last trial of
MWM training. In a standard probe trial, the goal platform is
removed and animals are returned to the maze for a specifi ed
amount of time, generally 60 s. The amount of time animal spent
in the quadrant where the goal was previously located during
acquisition can be calculated.
A visual platform version of the MWM can be done to ensure
performance is not affected by visual, motor, or other noncogni-
tive defi cits. In this version of the task, the platform should be
clearly visible to the animals.

2.1.2. Morris Water Maze
Procedure: Spatial
Navigation