Novel object recognition test
The NORT is used to evaluate declarative memory and object recognition
and has an essential application in the study of cognitive alterations.
The test was performed in a Plexiglas box (40 cm×40 cm×65 cm) and the
task procedures consist of three phases: habituation, training, and
test. The rats were habituated to the test box for 20 min on the
habituation phase (24 h before the training phase). During the training
phase, two identical objects were placed in opposite walls of the
testing box, and the animals were allowed to explore for 10 min. Then,
we changed one object to a different shape and color in the test phase,
and a test session of 10 min was performed after a retention interval of
either 2 h. The behavior of the subjects in each trial was recorded on
video, and the exploration time was scored by an observer blinded to the
experimental conditions. Exploration was defined as sniffing, biting,
licking or touching the object with the nose. Turning around or sitting
on the object was not considered exploratory behavior. During the test
session, a discrimination index (DI) was calculated using the formula
(B−A)/(B+A), with B being the time spent exploring the novel object and
A being the time spent exploring the familiar object.