Memory-dependent effects on palatability in mice

While palatability depends on the properties of particular foods, it is also determined by prior experience, suggesting that memory affects the hedonic value of a substance. Here, we report two procedures that affect palatability in mice: negative contrast and flavour habituation. A microstructure analysis of licking behaviour was employed, with the lick cluster size (the number of licks made in quick succession before a pause) used as a measure of palatability. It was first confirmed that lick cluster size increased monotonically as a function of sucrose concentration, whereas consumption followed an inverted U-shaped function. In a successive negative contrast procedure it was found that when shifted from a high sucrose concentration (32%) to a low sucrose concentration (4%), mice made smaller lick clusters than a group that only received the low concentration. Mice exposed to flavours (cherry or grape Kool Aid) mixed with sucrose (16%) made larger lick clusters for familiar flavours compared to novel flavours. This habituation effect was evident after short (5 min) and long (24 h) test intervals. Both successive negative contrast and flavour habituation failed to affect levels of consumption. Collectively, the results show that prior experience can have effects on lick cluster size that are equivalent to increasing or decreasing the sweetness of a solution. Thus, palatability is not a fixed property of a substance but is dependent on expectation or familiarity that occurs as a result of memory.