Taste preference simply means that an animal will choose certain types of food in preference to others, and the animal automatically uses this to help control the type of diet it eats. Furthermore, its taste preferences often change in accord with the body's need for certain specific substances.
The following experiments demonstrate this ability of animals to choose food in accord with the needs of their bodies. First, adrenalectomized, salt-depleted animals automatically select drinking water with a high concentration of sodium chloride in preference to pure water, and this is often sufficient to supply the needs of the body and prevent salt-depletion death. Second, an animal given injections of excessive amounts of insulin develops a depleted blood sugar, and the animal automatically chooses the sweetest food from among many samples. Third, calcium-depleted parathyroidectomized animals automatically choose drinking water with a high concentration of calcium chloride.
The same phenomena are also observed in everyday life. For instance, the "salt licks" of desert regions are known to attract animals from far and wide. Also, human beings reject any food that has an unpleasant affective sensation, which in many instances protects our bodies from undesirable substances.
The phenomenon of taste preference almost certainly results from some mechanism located in the central nervous system and not from a mechanism in the taste receptors themselves, although it is true that the receptors often become sensitized in favor of a needed nutrient. An important reason for believing that taste preference is mainly a central nervous system phenomenon is that previous experience with unpleasant or pleasant tastes plays a major role in determining one's taste preferences. For instance, if a person becomes sick soon after eating a particular type of food, the person generally develops a negative taste preference, or taste aversion, for that particular food thereafter; the same effect can be demonstrated in lower animals.
Organization of the olfactory membrane and olfactory bulb, and connections to the olfactory tract.
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