Journal: Journal of Neuroscience
Year: 2009
Keywords: amygdala, outcome representations, cues, incentive properties, reinforcement learning
- Summary
- The language used in (the abstract of) this paper is EXTREMELY confusing.
- Here's the gist: past research has examined the performance of BLA lesioned rats in devaluation procedures. It is clear that the BLA plays a role in the establishment of outcome representations that link cues to the incentive properties of reinforcers. The authors are asking what role the BLA plays once these outcome representations have been established.
- Two articles are cited in abstract:
- Pickens et. al (2003) found normal devaluation performance in rats when BLA lesions were made AFTER pavlovian light-food pairings but BEFORE devaluation by food-toxin pairings.
- Ostlund and Balleine (2008) found normal devaluation performance in rats when BLA lesions were MADE after instrumental training with MULTIPLE instrumental responses and food reinforcers but BEFORE devaluation of one reinforcer by selective satiation.
- They find here that when multiple reinforcers were used, POST-training BLA lesions disrupted the expression of devaluation performance in rats, using either pavlovian or instrumental training procedures and either conditioned taste aversion or satiation devaluation procedures.
- Introduction
- BLA damage shows impaired performance during reinforcer devaluation tasks.
- The value of the food reinforcer is reduced by satiation or food-toxin pairings after the completion of cue or response training.
- First Paradigm
- Animals are trained to associate either a neutral stimulus or a response with a particular reinforcer.
- AFTER training, the reinforcer is devalued by either motivational (e.g., prefeeding the reinforcer) or associative (e.g., pairing the reinforcer with illness)
- Finally, cue OR response performance is assessed, usually in the absence of the reinforcer.
- Normal animals show spontaneous reductions in performance, whereas animals with PREtraining BLA lesions typically do NOT.
- Pickens et al. (2003)
- Said BLA is required ONLY for acquisition of such outcome representations but NOT for maintaining them, modifying them, or using them to guide subsequent behavior. Found that rats lesioned AFTER conditioning but BEFORE devaluation of the food by food-illness pairings showed NORMAL devaluation effects.
- Ostlund and Balleine (2008) found that intact BLA function was required for integrating changes in reinforcer value with PREVIOUSLY acquired reinforcer representations to guide performance.
- Differences in the Paradigms
- Pickens et al. (2003)
- Associative conditioning
- Single reinforcer
- Taste aversion
- Ostlund and Balleine (2008)
- Instrumental conditioning
- Multiple reinforcers
- Selective satiation
- This paper's experiments are used to examine the role of training contingency and devaluation procedure in determining the effects of post-training BLA lesions on reinforcer devaluation performance in rats trained with multiple reinforcers
- Multiple outcome instrumental training
- Effects of devaluation by selective satiation
- Effects of devaluation by food-illness pairings
- Multiple outcome pavlovian training
- Effects of devaluation by selective satiation
- Effects of devaluation by food-illness pairings
- Material and Methods
- Materials
- Subjects
- Male, Long-Evans rats
- Surgeries
- NMDA lesions to LA in each hemisphere.
- N
- 1: 8, 8
- 2: 9, 10
- 3, 4: 8, 8
- Methods
- Experiment 1
- Food-cup training
- Rats food-deprived to 85% of body weight
- Preexposed for 2 h to each reinforcer
- orange or grape Kool-Aid
- 64-min food cup training session on each of 2 consecutive days
- Each session yielded 16 deliveries of a specific reinforcer and order of flavor presentation was counterbalanced.
- Instrumental training
- 2 instrumental training sessions per day separated by 2 h each
- 1 with left only 1 with right
- order alternated daily
- Response-outcome contingencies fully counterbalanced such that for half of the rats left lever responses resulted in delivery of grape and responses on the right lever produced delivery of orange, whereas the remaining rats were assigned the opposite contingencies
- First 3 days
- 30 min sessions in which each response was reinforced on fixed-interval schedule
- Then 20 min sessions and reinforcer delivery switched to random ratio schedule of reinforcement leading to 14 total sessions
- On average every 5 responses resulted in reinforcer delivery
- 3, 3, 3, 5: 5, 10, 15, 20
- number of sessions : average number of responses until reinforcement delivery
- Instrumental reinforcer devaluation: sensory specific satiety, extinction, and choice test
- After surgery, rats were prefed with one of the two possible outcomes.
- Identity of the solution was counterbalanced across the previous response-outcome contingencies
- After 2 h rats were given a 20-min extinction test
- no reinforcements were given with responses
- except now both levers are available for responding
- What's the point?
- absence of the reinforcers ensures that test performance reflects an interaction of response-outcome information acquired during initial training with some internal representation of the status of the outcome as a goal after satiety treatment. To the extent that responding was controlled by the current value of the reinforcer anticipated after each of the two responses (left and right lever presses), rats would preferentially perform the response that had been reinforced previously with the reinforcer that had not been prefed (i.e., the non-devalued response).
- Effectiveness of the prefeeding devaluation treatment in altering the rats' preference for a reinforcer.
- Each rat given access to two drinking bottles in its home cage, one containing 25 ml of the prefed reinforcer and the other containing 25 ml of the other reinforcer
- You'd expect that consumption would be greater for the non-prefed reinforcer
- Experiment 2
- Instrumental training
- Same as experiment 1
- Instrumental reinforcer devaluation: conditioned taste aversion, extinction, and choice test
- Reinforcer paired with LiCl
- Days 1, 3, and 5
- All rats received 50 ml of the paired reinforcer for 15 min, followed by an injection of 0.3 M LiCl at 5 ml/kg
- Days 2, 4, and 6
- all rats received 50 ml of the unpaired reinforcer for 15 min
- Extinction test same as experiment 1
- To confirm the taste aversion readily transferred to the operant chambers, a 15 min consumption choice test was performed with rats given 25 ml of simultaneous access to both reinforcers in metal cups attached to the chamber floors.
- Experiment 3
- Pavlovian training
- Food-cup like experiment 1
- Two sessions per day ISI: 2 h
- 1 with 1500 kHz tone, 1 with white noise
- five 10s presentations of the stimulus, followed by delivery of 0.1 ml of either grape or orange solution, with a variable ITI that averaged 4 min.
- Rats received a total of 10 sessions of pavlovian training, order of sessions alternating daily
- After completion neurotoxic BLA surgeries were given, other half of rats were given sham lesions
- Pavlovian reinforcer devaluation: conditioned taste aversion, extinction, choice test
- After recovery experiment 2 taste aversion condition was given
- Pavlovian extinction test
- four 10s presentation of each stimulus tone and noise with a 4 min fixed interval between stimulus presentations
- Experiment 4
- Same as 3 except sensory-specific procedures that were the same as 1 were used to devalue on reinforcer before the extinction and reinforcer choice tests
- Results
- BLA lesions were large ~90% damage to lateral, basal, and accessory basal nuclei and 50% damage to ant and post basomedial nuclei.
- Experiment 1
- Instrumental training
- All rats displayed similar rates of responding for both reinforcers and increased their response rates after increments int he response-reinforcer schedule (as expected).
- No interactions
- Extinction test
- Sham-lesioned rats that were prefed resulted in a suppression of responding to the lever previously associated with that reinforcer compared with responding on the alternate (non-devalued) lever.
- BLA-lesioned rats displayed a small preference for the lever associated with the devalued reinforcer.
- Lesion-response interaction
- What exactly does this mean?
- Discussion
- Questions
- Why could any of the differences in the experimental paradigms have contributed to the different outcomes observed?
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