Sequential behaviour in the Rat: Design and applications of a Serial Reaction Time Task
The study of sequential behaviour which relies among others on dopamine mechanisms and basal ganglia networks, is particularly relevant in Parkinsonian patients. Sequential behaviour can be ex- tensively studied through the use of a standard test known as the Serial Reaction Time Task (SRTT) in...
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|Summary:||The study of sequential behaviour which relies among others on
dopamine mechanisms and basal ganglia networks, is particularly
relevant in Parkinsonian patients. Sequential behaviour can be ex-
tensively studied through the use of a standard test known as the
Serial Reaction Time Task (SRTT) in humans and non-human pri-
mates. Although a rodent model of such a test would be very useful
to investigate the underlying brain mechanisms of this type of learn-
ing, there is no standardised rodent test. The aim of the three studies
presented in this work was to characterise sequential behaviour in
the intact rat as an analogy to the human standard test.
The aim of the first study was to implement a rat model of the hu-
man standard SRTT. The designed task required the rats to poke fast
with their nose (motor answer) into lit holes (visual stimulus, one of
four locations) and to perform a series of such nosepokes in order
to get a food-reward, according to a fixed ratio schedule of reinforce-
ment (FR). The location of the light was displayed in either random
or sequential order and sequential learning was inferred from the dif-
ference in performance between the two conditions within-session.
We found that the rats performed better in the sequential condition, in
terms of speed, accuracy and number of rewards earned. Details of
the test were improved in the course of the studies to ensure that the
better performance in sequential condition could only be attributed to
the learning of the serial order information and no other general skill.
Rats were finally tested on a repeated sequence of twelve ordered
locations under a FR13. The length of the FR13 series was intention-
ally longer than the length of the repeated sequence to dissociate the
sequence locations from the FR schedule positions. The sequence
structure was cautiously generated according to statistical rules (e.g.
locations frequency, transitions frequency). These features provided
a level of sequence difficulty comparable to the human one.
This test was used in the second study to investigate the role of
dopamine in this task in general and in the sequential performance
of well-trained rats in particular. As this SRTT was planned to be
applied in dopamine-depleted rats, the effects of the blockade of the
dopaminergic transmission were first studied. A D1 and a D2 se-
lective antagonists were used and injected systemically. We found
that both antagonists produced dramatic disruption of responding,
decreased response rate and increased the number of omissions.
Only the D1 antagonist increased accuracy to a small extent. These
effects were independent of the condition and dose-dependent. The
D1 antagonist specifically impaired initial reaction times (within the
first halves) of the series, whereas the D2 antagonist affected the
whole pattern. Under D1 antagonist treatment, reaction times did
not improve in sequential condition compared to random condition,
which would reflect a specific effect of the D1 receptor in sequential
The third study aimed at investigating to which extent well-trained rats
in the SRTT developed a habit. Rats were trained in sequential con-
dition and were then confronted during a test with randomly inserted
unique sequence violations. A detailed analysis of the performance
yielded that rats showed indices of habit but also that attention was
still playing a role. At the position of the violation, either the rats dis-
played lengthened reaction times for correct pokes or poked fast into
the hole where the light should have appeared according to the se-
quential order (“expected” light location). This fast answer was how-
ever now incorrect because of the sequence violation. Repetition of
this test in a bigger group of rats proved the reliability of these results.
In this repeated experiment, the apparatus and details of the task (but
not of the sequence) were modified to suit application in dopamine-
depleted animals for which motor requirements for example, have to
The rat SRTT with food-reinforcement described here shows high
face-validity with the standard human SRTT. It has been effective
for the biopsychological characterisation in intact rats of sequential
performance, which in many aspects resembled the human one. The
designed SRTT with food-reinforcement will probably be of value as
a rodent model for the study of sequential behaviour in dopamine-
depleted animals as a model for Parkinson disease.|
|Physical Description:||118 Pages|