The Probert Encyclopaedia of Medicine

TASTE

The different papilla on the tongue show some area-specific patterns of taste selectivity. There are four basic tastes: sweet, sour, salt, and bitter. The flavours that are tasted are actually combinations of the four tastes. The sides of the tongue tend to be sensitive to sour and salt closer to the apex. The tip tends to be sensitive to sweet, while the back of the tongue is most sensitive to bitter. The common experience that some sweet substances, such as saccharin, have a bitter aftertaste is partly a result of the area-specific patterns of taste. The sweet taste is experienced first, at the tip of the tongue, but is mixed with bitterness as the substance moves toward the back of the tongue.
Research Taste