Neuronal processing of natural rewards

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BECKER, Christoph Alexander, 2017. Neuronal processing of natural rewards [Dissertation]. Konstanz: University of Konstanz

@phdthesis{Becker2017Neuro-38988, title={Neuronal processing of natural rewards}, year={2017}, author={Becker, Christoph Alexander}, address={Konstanz}, school={Universität Konstanz} }

Food and fluid ingestion is of primal importance for the survival of an organism. In this vein, the power of respective goal stimuli to drive motivation needs to be regulated in accordance with internal needs during anticipation and updated on a moment-to-moment basis during consumption. However, the intake of pathogenic foods can cause substantial threat to health and well-being. Thus, fast and automatic mechanisms ensure that inedible foods evoke strong reactions of disgust and that these foods are rejected accordingly. Previous studies have shown that the depletion of an organism and stimulus edibility are major contributors modulating the incentive value of natural rewards. While a large body of studies examined the effects of these internal and external factors in behavioral paradigms, much less knowledge does exist about their underlying neuronal mechanisms. Therefore, functional imaging studies were conducted to advance the understanding of natural reward processing in humans.<br /><br />The first study addressed the question which neural structures are engaged in increasing the incentive value of need-relevant stimuli during anticipation. Therefore, participants were scanned twice – either in a thirst or a no-thirst state – while viewing pictures of beverages and chairs. Results revealed selectively increased BOLD responses for beverages in the aMCC, insula, and amygdala during the thirst as compared to the no- thirst state. This finding demonstrates the increased attribution of incentive value specifically for the need-relevant category during anticipation.<br /><br />The second study addressed the question which neural structures are engaged in the shift of stimulus value during consummation. Therefore, participants were scanned while being in a thirsty state and, over the course of the experiment, received small amounts of water sufficient for satiation. Results revealed a linear decrease of the BOLD response in the aMCC and posterior insula in relation to water consumption. This finding demonstrates a dynamic need-state dependent representation of incentive value.<br /><br />The third study addressed the question of how neural structures are engaged in the detection of food edibility during the anticipatory phase. Therefore, participants were scanned with MRI and EEG while viewing images of foods at various stages of natural decay. The MRI results revealed increased BOLD activations in the extrastriate cortex during the processing of inedible as compared to edible food items. The EEG results further extend this finding by demonstrating a fast discrimination of food edibility (< 200 ms) and an increased LPP for inedible foods. Consequently, these findings demonstrate the brains sensitivity to harmful stimuli presumably supporting the avoidance of pathogen intake.<br /><br />Taken together, the findings presented in Study 1 and Study 2 demonstrate that the incentive value of goal stimuli is selectively enhanced during anticipation and dynamically adjusted on a moment-to-moment basis during consummation, i.e., adjusted accordingly in relation to the motivational significance of the stimulus. Furthermore, the findings in Study 3 demonstrate a fast discrimination in food edibility and increased attention towards these stimuli, which supports the idea of a behavioral immune system for pathogen avoidance. In sum, the results reported in the present dissertation extend existing knowledge by advancing the understanding of how neural mechanisms turn the sight of environmental stimuli into adaptive behavioral responses. 2017-05-22T09:10:25Z Becker, Christoph Alexander eng terms-of-use Becker, Christoph Alexander 2017-05-22T09:10:25Z Neuronal processing of natural rewards 2017

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