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Role of the anterior cingulate cortex in the control over behaviour
by Pavlovian conditioned stimuli in rats
R.N. Cardinal1*. J.A. Parkinson2, H. Djafari Marbini1, A.J. Toner1, T.W. Robbins1, B.J. Everitt1
1. Exp Psychol, 2. Anatomy, Univ Cambridge, Cambridge CB2 3EB, United Kingdom
The anterior cingulate cortex (Ant Cing) in the rat has previously been
shown to be critical for the acquisition of autoshaping, a measure of Pavlovian
conditioning in which animals come to approach a conditioned stimulus (CS+)
that predicts food delivery, and not to approach a second, nonpredictive
stimulus (CS–). Here we demonstrate that Ant Cing lesions do not impair
the acquisition of temporally discriminated approach to a single magazine
light CS that predicts food. Lesioned animals were able to respond instrumentally
for this CS, now acting as a conditioned reinforcer, and the potentiation
of responding by intra-accumbens amphetamine was unaffected. Lesioned rats
also acquired a normal freezing response to a discrete CS paired with footshock.
However, these same subjects were impaired at autoshaping. A second group
of Ant Cing-lesioned rats were tested on a Pavlovian-instrumental transfer
task, in which an appetitive CS potentiates ongoing instrumental responding,
and no impairment was found.
These results suggested that the Ant Cing is only critical for the normal expression of appetitive conditioning when multiple stimuli must be discriminated or disambiguated on the basis of their association with reward. To test this hypothesis, a third group of Ant Cing-lesioned rats were trained on a temporally discriminated approach task using two stimuli (a CS+ and a CS–). In support of the disambiguation hypothesis, while sham-operated controls approached the source of food during the CS+ more than during the CS–, Ant Cing-lesioned rats failed to discriminate, approaching equally during both stimuli.
Supported by: MRC (UK)
Key words: autoshaping, discrimination, motivation, appetitive