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Rats, like humans, are born with only a few innate flavor preferences and aversions. Preferences retain great plasticity throughout the lifespan because they are sensitive to modification by experience. From an early age, rats can rapidly learn to prefer or avoid a flavor (conditioned stimulus, CS) that is associated with a positive or negative unconditioned stimulus (US). The US may be the mother's milk, social or thermotactile stimulation, or other food-related stimuli. Flavor-flavor learning occurs when the CS flavor is mixed with a naturally preferred (e.g., sweet) or avoided (e.g., bitter) US flavor. Flavor preferences and aversions are also produced by USs that have postoral positive (e.g., nutritious) or negative (e.g., toxic) actions. These types of learning appear to involve different behavioral and neural mechanisms as indicated by differences in conditioned responses, effective temporal parameters, resistance to extinction, and neurochemical mechanisms. New evidence indicates that flavor-nutrient preference learning can occur before weaning and influence food selection after weaning. Flavor conditioning not only affects food choice, but can also significantly increase food acceptance, that is, total consumption. Thus, from an early age, learning processes shape the feeding behavior of animals. While primarily serving an adaptive function, learning may play a role in biasing individuals towards excessive intake and weight gain.

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The palatable, energy-dense foods that characterize modern environments can promote unhealthy eating habits, along with humans' predispositions to accept sweet tastes and reject those that are sour or bitter. Yet food preferences are malleable, and examining food preference learning during early life can highlight ways to promote acceptance of healthier foods. This narrative review describes research from the past 10 years focused on food preference learning from the prenatal period through early childhood (ages 2-5 years). Exposure to a variety of healthy foods from the start, including during the prenatal period, early milk-feeding and the introduction to complementary foods and beverages, can support subsequent acceptance of those foods. Yet development is plastic, and healthier food preferences can still be promoted after infancy. In early childhood, research supports starting with the simplest strategies, such as repeated exposure and modelling, reserving other strategies for use when needed to motivate the initial tasting necessary for repeated exposure effects to begin. This review can help caregivers and practitioners to promote the development of healthy food preferences early in life. Specific implementation recommendations, the role of individual differences and next steps for research in this area are also discussed.

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Unlike older animals, weanling-age rats do not seek water to drink when they are dehydrated, despite the fact that a physiological sensitivity to dehydration is present very soon after birth. We demonstrate here that the appetitive behaviors needed to approach and obtain water become linked to dehydration only as a result of specific postnatal learning experience. Preventing early experience with dehydration retards the developmental emergence of dehydration-induced, water-oriented behavior in young rats. But a single pairing of water with dehydration can establish an appetitive response. These findings reveal a critical role of early learning in the development of goal-oriented behavior. Such a learning process is potentially characteristic of other behavioral systems, from the most basic appetites to complex motives.

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