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Reward modulation of cognitive function: the nucleus accumbens
floors and peppermint scent).
Behavioural procedures
We aimed to develop a paradigm similar to the paradigm studied extensively in humans. A
detailed description of the paradigm used in humans can be found elsewhere (Aarts et al.,
2010; van Holstein et al., 2011; Aarts et al., 2015).
In the rodent version of this paradigm, animals received pre-training-, discrimination
training-, and finally test sessions, each of which took place in either reward context (RC-A
or RC-B). Each animal always received either one or three food pellets in a certain context,
i.e. half the animals always received one pellet per reward delivery in RC-A (low reward
condition) and three pellets in RC-B (high reward condition), whereas the other animals
received the opposite arrangement. Each animal received two training sessions or tests per
day (separated by at least 4 hours); one in a high- and one in a low reward context, the order
of which was counterbalanced.
Pre-training and discrimination training procedures, with the exception of the reward
context, were similar to previously described by Haddon and Killcross (2006). All sessions
took place in either a high or low reward context (counterbalanced).
Training procedure
Pre-training
After 4 days of food deprivation, rats were given two 30 min sessions of magazine training.
During each session a reward (1 or 3 pellets, depending on the context) was delivered on
average every 60 seconds. On the following four days, rats received two daily 36 min sessions
of lever press training. During these sessions levers were extended for 60 s each in random
alternation (6 left and 6 right lever presentations) with a variable inter-trial-interval of 45-195
s (mean 120s). Initially lever pressing took place at a continuous reinforcement schedule
(resulting in one or three pellets, depending on the context). On the second day this was
increased to a RI15 schedule, which remained in place for the remainder of the experiment.
Discrimination training
Animals received two sessions (of ~ 85 minutes each) of discrimination training on each
day for 15 days. In one training session, rats were presented with two auditory stimuli (A1
and A2) and on the alternate training session, rats were presented with two visual (V1 and
V2) stimuli, during which both left and right levers were available but only one of the levers
rewarded. Within each modality, one of the stimuli (A1 during auditory sessions and V1
during visual sessions) indicated that left but not right lever presses would be rewarded,
whereas the other stimuli (A2 and V2) indicated the opposite arrangement (e.g. A1-L, A2-R