Flavors Paired With Internal Pain or With Nausea Elicit Divergent Types of Hedonic Responses
Pairing a taste with either internal pain (e.g., from hypertonic saline injection) or nausea (e.g., from LiCl administration) will reduce subsequent consumption of that taste. Here we examine the responses to a taste paired with either hypertonic saline or LiCl using the analysis of licking microstructure (mean lick cluster size: Experiments 1–3), taste reactivity (examining the distribution of appetitive and aversive orofacial responses: Experiments 2–3), and immobility (as a measure of fear: Experiments 2–3). At both high (10 ml/kg 0.15 M LiCl, 10 ml/kg 1.5 M NaCl) and low dose levels (2 ml/kg 0.15 M LiCl, 4 ml/kg 1.5 M NaCl), pairing a taste with either LiCl-induced nausea or internal pain produced by hypertonic NaCl caused reductions in voluntary consumption, in appetitive taste reactivity responses, and in lick cluster size. However, only pairing with LiCl resulted in conditioned aversive taste reactivity responses to the taste. In contrast, pairing with hypertonic NaCl resulted in the taste eliciting higher levels of immobility (reflecting fear) than did pairing the taste with LiCl. The clearly dissociable effects of LiCl and hypertonic saline on aversive taste reactivity and fear responses, despite equivalent effects on consumption, demonstrates selective conditioning effects between internal pain and nausea.