Proefschrift_Holstein

Chapter 6

A well-established paradigm to assess the effect of reward on flexible behaviour in human subjects is the rewarded task-switching paradigm (Aarts et al., 2010; van Holstein et al., 2011; Aarts et al., 2014a; Aarts et al., 2015; Etzel et al., 2015; Fuentes-Claramonte et al., 2015), which allows the assessment of flexible control in low and high reward conditions separately. A similar rodent paradigm that can tap into these processes, i.e. switching between tasks based on external cues and the effect of reward motivation on this cognitive process, will help the advancement of understanding the neural mechanisms underlying this process in a manner that is unconfounded by learning and working memory. In the current study we developed such a paradigm in rodents, and subsequently assessed whether lesions of the AcbC impair successful motivation-cognition integration. Twenty-four experimentally naive male hoodedWistar rats were used as subjects. The animals were housed in yellow-tinted plastic boxes located in a temperature and humidity -controlled colony room. They were housed in twos or threes and maintained on a 12 h light/dark cycle. Animals were handled daily for 4 days before training and were kept on a food deprivation schedule during training and testing to maintain them at ~85% of their free feeding weight. All procedures were approved by the Animal Ethics Committee at the University of Sydney. Apparatus and stimuli Training and testing took place in 16 MED Associates (East Fairfield, VT) operant chambers (32 x 25 x 25 cm) with a transparent Perspex ceiling, wall and door. Each operant chamber was enclosed in sound- and light-resistant cabinets and equipped with a pellet dispenser that delivered grain pellets (45mg, BioServe Biotechnologies, Beltsville, MD) into a recessed food magazine. The chamber contained two retractable levers at either side of the magazine. Visual stimuli consisted of a panel light (flashing or steady) above each lever. Auditory stimuli (~80dB) were produced by a 28V DC mechanical relay that delivered a 5Hz clicker sound and a sonalert that delivered a 3kHz tone. Task cues were the house light (3W, 24 V) located on the wall opposite the magazine and white noise produced by a white noise generator. Two computers running MED Associates software controlled the experimental events and recorded lever presses. All stimuli were presented against a background sound produced by the ventilation fan (~60 dB). To signal the reward condition (i.e. high or low reward), the physical appearance of the boxes was manipulated by placing wallpaper behind the Perspex (black and white stripes or black dots on a white background), by placing floorboards on top of the stainless steel floors (smooth black or coarse transparent plastic) and by delivering a distinct scent (vanilla or peppermint) to each chamber before the start of a session. This resulted in two distinct reward contexts; RC-A (striped wallpaper, smooth floors, vanilla scent), and RC-B (dotted wallpapers, coarse Methods Subjects

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