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dc.contributor.advisorWinn, Philip
dc.contributor.authorMacLaren, Duncan A. A.
dc.description.abstractLocated in the mesopontine tegmentum, the pedunculopontine tegmental nucleus (PPTg) is comprised principally of glutamatergic, cholinergic and GABAergic neurons. In addition to being fully integrated into basal ganglia, PPTg projects to thalamus and motor output sites in the brainstem. Previous studies have shown a range of behavioural changes after PPTg manipulation. Prominent amongst these is an apparent deficit in the ability to learn the consequences of actions. PPTg is divisible into a posterior component (pPPTg) in receipt of rapid polymodal sensory input and projecting into VTA/SNc dopamine neurons and an anterior component (aPPTg) in receipt of basal ganglia outflow and projecting into SNc and lower brainstem structures. The research described here assesses the role of the pPPTg in instrumental learning. Using a contingency degradation paradigm, it was shown that inactivation of the pPPTg (by muscimol microinfusion) specifically blocked the updating of associations between actions and outcomes, without the affecting the ability to re-execute previously learned instrumental actions. Selective bilateral destruction of pPPTg cholinergic neurons (with the fusion toxin diphtheria toxin – urotensin II [Dtx-UII]) resulted in >90% loss of pPPTg cholinergic neurons. These lesions produced no detectable changes on any measured aspect of an instrumental learning task consisting of various fixed and variable ratio schedules of reinforcement and extinction. Subsequent experiments found that the same selective cholinergic pPPTg lesions also produced no changes in the locomotor response to nicotine or rate of nicotine sensitisation. These results are the first to demonstrate a brainstem role in action-outcome learning. Results support the view that PPTg performs a ‘first pass’ analysis on incoming sensory data and interfaces salient aspects of this with appropriate basal ganglia and brainstem circuitry, with glutamatergic pPPTg projections sending an essential signal and cholinergic projections performing as part of a wider modulatory system.en_US
dc.publisherUniversity of St Andrews
dc.subjectBasal gangliaen_US
dc.subject.lcshOperant conditioning--Physiological aspectsen_US
dc.subject.lcshLearning--Physiological aspectsen_US
dc.subject.lcshPons Varolii--Physiologyen_US
dc.subject.lcshPons Varolii--Effect of chemicals onen_US
dc.titleLinking actions to outcomes : the role of the posterior pedunculopontine tegmental nucleus in instrumental learningen_US
dc.contributor.sponsorWellcome Trusten_US
dc.contributor.sponsorUniversity of St Andrews. School of Psychologyen_US
dc.type.qualificationnamePhD Doctor of Philosophyen_US
dc.publisher.institutionThe University of St Andrewsen_US

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