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Abstract
The present thesis examined the role of the rodent lateral orbitofrontal cortex (LO) in controlling performance in Pavlovian cue-outcome learning and placed the function of LO in the broader context of the entire orbitofrontal cortex (OFC) region. We found that functional inactivation of LO disrupted the retention of between- but not within-session extinction behaviour. This finding was not due to the disruption of post-session memory consolidation processes by the functional inactivation of LO or impaired acquisition of Pavlovian conditioned inhibition learning. These data confirmed that LO is necessary for the acquisition of Pavlovian extinction learning.
In a second set of experiments we investigated the role of LO in guiding behaviour using the sensory specific properties of expected outcomes. Pre-training LO lesions were found to disrupt Pavlovian devaluation by taste aversion but not specific satiety or instrumental devaluation by conditioned taste aversion, or the specific Pavlovian-to-instrumental transfer effect. These findings rule out an explanation of LO function in simply representing the sensory specific properties of expected outcomes.
The third set of experiments examined the role of LO in the acquisition of simple Pavlovian learning. Pre-training LO lesions increased conditioned responding whereas post-training lesions and functional inactivation of LO decreased conditioned responding. A blocking procedure revealed that decreased responding following LO inactivation did not affect the subsequent blocking of new learning at test. Furthermore, LO inactivation impaired the use of current relative value of outcomes to modulate behaviour. This suggested a role for LO in the expression of conditioned responding but not initial Pavlovian learning.
A final set of experiments examined the role of LO in a novel Pavlovian differential outcomes expectancy task. Pre-training LO lesions were found to decrease whereas post-training lesions were found to increase response accurate responding. This pattern of results, in combination with the opposite effect of pre- and post-training lesions in simple Pavlovian conditioning demonstrated the importance of LO in guiding Pavlovian behaviour. Taken together, these data demonstrated a role for LO in the integration of sensory and motivational properties of expected outcomes to flexibly control Pavlovian behaviour.