Objective: Investigate the effect of orbitofrontal cortex (OFC) lesions on conditioned responses to a visual stimulus associated with food reinforcement, and test whether OFC-lesioned rats can adjust their responding when the incentive value of the reinforcer is devalued
Materials & Equipment Checklist
6 items1 from ConductScience
Gather these items before starting the experiment. Check off items as you prepare.
Equipment4
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Protocol Steps
View Abstract
Clinical evidence indicates that damage to ventromedial prefrontal cortex disrupts goal-directed actions that are guided by motivational and emotional factors. As a consequence, patients with such damage characteristically engage in maladaptive behaviors. Other research has shown that neurons in the corresponding orbital region of prefrontal cortex in laboratory animals encode information regarding the incentive properties of goals or expected events. The present study investigates the effect of neurotoxic orbitofrontal cortex (OFC) lesions in the rat on responses that are normally influenced by associations between a conditioned stimulus (CS) and the incentive value of reinforcement. Rats were first trained to associate a visual CS with delivery of food pellets to a food cup. As a consequence of learning, rats approached the food cup during the CS in anticipation of reinforcement. In a second training phase, injection of LiCl followed consumption of the food unconditioned stimulus (US) in the home cage, a procedure used to alter the incentive value of the US. Subsequently, rats were returned to the conditioning chamber, and their responding to the CS in the absence of the food US was tested. Lesions of OFC did not affect either the initial acquisition of a conditioned response to the light CS in the first training phase or taste aversion learning in the second training phase. In the test for devaluation, however, OFC rats exhibited no change in conditioned responding to the visual CS. This outcome contrasts with the behavior of control rats; after devaluation of the US a significant decrease occurred in approach to the food cup during presentation of the CS. The results reveal an inability of a cue to access representational information about the incentive value of associated reinforcement after OFC damage.
1
Initial Conditioned Response Acquisition Training
Rats are trained to associate a visual conditioned stimulus (light) with delivery of food pellets to a food cup. Through repeated pairings, rats learn to approach the food cup during presentation of the visual CS in anticipation of food reinforcement.
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Note: This is the first training phase where conditioned responding is acquired
View evidence from paper
“Rats were first trained to associate a visual CS with delivery of food pellets to a food cup. As a consequence of learning, rats approached the food cup during the CS in anticipation of reinforcement”
2
Taste Aversion Learning (US Devaluation)
In the home cage, rats consume food pellets followed by injection of lithium chloride (LiCl). This procedure creates a taste aversion and alters the incentive value of the food US, making it less desirable.
Note: This is the second training phase designed to devalue the unconditioned stimulus
View evidence from paper
“In a second training phase, injection of LiCl followed consumption of the food unconditioned stimulus (US) in the home cage, a procedure used to alter the incentive value of the US”
3
Test for Devaluation in Conditioning Chamber
Rats are returned to the conditioning chamber and tested for their responding to the visual CS in the absence of the food US. Approach behavior to the food cup during CS presentation is measured to determine if rats adjust their conditioned responding based on the devalued incentive value of the reinforcer.
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Note: This test reveals whether the CS can access representational information about the incentive value of the associated reinforcement
View evidence from paper
“Subsequently, rats were returned to the conditioning chamber, and their responding to the CS in the absence of the food US was tested”
