Mitchell et al (2012) used a “nose poke” exercise to investigate reward sensitivity in rats. Single food pellets were used as the low value reward and four food pellets as the high value reward. Following an unexpected downshift from four to one food pellet, rats took significantly longer to collect the reward than those rats that had always received one pellet.
Gomez et al (2009) found that rats drank significantly less 4% sugar solution (low value) when downshifted unexpectedly from a 32% solution (high value) compared to rats that had only ever received 4% sucrose solution. They also found that this effect was enhanced in a “more emotional” strain of rat.
Papini et al (1988) observed similar effects for red opossums (Lutreolina crassicaudata) and white-eared opossums (Didelphis albiventis), with those individuals that had been downshifted from a 32% sucrose solution (high value) to a 4% solution (low value) consuming less than those that had always been given the 4% solution.
Bentosela et al (2009) used a novel learning task to assess reward sensitivity in owned dogs. This involved giving dogs a food reward in exchange for the dog directing an eye gaze towards the experimenter. Dogs in the downshifted group (switched from liver (high value) to kibble (low value)) rejected food more often and gazed less at the experimenter compared to dogs in the unshifted group that had always received the kibble.
What do we know so far in relation to dogs?
Previous work by Bentosela et al (2009) suggests that owned dogs are able to demonstrate reward sensitivity in relation to a task where they have to ‘work’ to get the reward. However, as this is the only study, to our knowledge, that has aimed to investigate this effect in dogs, little is known as to how robust the paradigm is within the species and whether or not this reward sensitivity is influenced by affective state.
We are therefore interested in creating a robust and reliable method of assessing reward sensitivity in dogs – both owned and unowned (i.e. rescue) dogs.