Assessment of taste reactivity has also been used to index the hedonic properties (or “liking”) of taste stimuli, with this response highly conserved across species (for reviews see Berridge, 2007; Grill & Berridge 1985). For instance, rhythmic or lateral tongue protrusions are exhibited in response to delivery of a palatable taste (positive responses), whereas aversive tastes elicit other responses such as a gaping reaction (Berridge & Treit, 1986; Grill & Norgren, 1978). The number and intensity of the positive responses to palatable solutions has been suggested to index the positive hedonic properties attributed to the solution by the test subject (Grill & Berridge, 1985). In a series of experiments examining taste reactivity among adolescents and adults to various concentrations of sucrose and other solutions delivered through intraoral cannulae, adolescent rats have been consistently shown to exhibit greater positive taste responses (e.g. more rhythmic and lateral tongue protrusions) than adults (Wilmouth & Spear, 2009). Such increases in positive taste reactivity and sucrose intake among adolescents are reminiscent of the greater motivation for natural, drug and alcohol rewards revealed in the CPP,
