Licking and Liking: The Assessment of Hedonic Responses in Rodents

Abstract

Affective processes are a key determinant of behaviour: At its simplest, liked stimuli are approached while disliked stimuli are avoided. Although assessing hedonic responses in nonverbal animals can be difficult, one relatively tractable approach relies on detailed analyses of rodents' consummatory behaviour. Rodents typically produce rhythmic sets of licks that can be grouped into clusters on the basis of the intervals between licks. The mean number of licks in a cluster (cluster size) is directly related to the concentration of palatable and unpalatable solutions. These relationships suggest that lick cluster size might be a useful index of an animal's hedonic reaction to the solution being consumed. I begin by reviewing studies of conditioned flavour preference and aversion that support the idea that lick cluster size can provide useful information about rats' hedonic reactions. I then describe how this methodology has been used to address previously intractable issues in the investigation of contrast effects as well as revealing an analogue of effort justification effects that, in humans, are commonly explained in terms of cognitive dissonance reduction. Finally, I consider how lick analysis might provide information about hedonic responses in animal models of human psychiatric disorders. In all these cases, how an animal did something was particularly informative about why it was doing it.

Nonreinforced flavor exposure attenuates the effects of conditioned taste aversion on both flavor consumption and cue palatability

“…Thus, LI joins a number of other manipulations that have parallel effects on these two measures (for a review, see Dwyer, 2012). Such results suggest that microstructural analysis of lick patterns and taste reactivity may be complementary measures that both assess taste palatability or hedonic responses.…”

“…A cluster was defined as a set of licks, each separated by an interlick interval of no more than 0.5 s. This criterion was used by Davis and his coworkers (e.g., Davis & Perez, 1993;Davis & Smith, 1992) and in the majority of our previous studies using lick analysis techniques (for a review, see Dwyer, 2012). Although other criteria have been used (e.g., Dwyer, Pincham, Thein, & Harris, 2009;Spector, Klumpp, & Kaplan, 1998), parametric analyses suggested that there is little practical difference between them, as most pauses greater than 0.5 s are also greater than 1 s (e.g., Davis & Smith, 1992;.…”

“…This was achieved by the microstructural analysis of licking behavior during voluntary consumption (for reviews of this methodology, see Davis, 1973Davis, , 1989Dwyer, 2012). The ingestive behavior of rats consuming fluids consists of sustained runs of rapidly occurring rhythmic licks (referred to here as clusters)…”

Microstructural analysis of negative anticipatory contrast: A reconsideration of the devaluation account

“…Conversely, when rats consume an unpalatable solution (such as quinine), lick cluster size bears a negative monotonic relationship with the concentration of the solution (Hsiao & Fan, 1993;Spector & St John, 1998). This has led to the idea that lick cluster size measures can be used as a reliable index of stimulus palatability and, hence, the affective component of reward value (see Dwyer, 2012, for a recent review). Critically, lick cluster size is at least partially independent of consumption, which typically displays an inverted U-shaped function between concentration and total consumption, with intermediate concentrations of palatable solutions eliciting the highest levels of intake (e.g., Richter & Campbell, 1940).…”

“…Critically, lick cluster size is at least partially independent of consumption, which typically displays an inverted U-shaped function between concentration and total consumption, with intermediate concentrations of palatable solutions eliciting the highest levels of intake (e.g., Richter & Campbell, 1940). As reviewed by Dwyer (2012), the dissociation between the two measures has been confirmed through flavor preference and aversion conditioning studies, which have demonstrated that some manipulations can influence lick cluster sizes, while leaving total consumption unchanged, and vice versa. Furthermore, it has been demonstrated that some taste aversions result in changes in lick cluster size that are analogous to actually changing a pleasant-tasting solution to an aversive one, while flavor preference conditioning result in changes that are analogous to changing the solution from a neutral to a palatable taste.…”