Functionally, these neurons are either motor (conducting impulses that will cause activity such as the contraction of muscles) or association (conducting impulses and permitting 'communication' between neurons within the central nervous system).
The scant research that has been done on the causes of pica suggests that the disorder is a specific appetite caused by mineral deficiency in many cases, such as iron deficiency, which sometimes is a result of celiac disease or hookworm infection.
A French study found that 44 percent of patients reported regularly eating non-food stuffs, such as clay, ashes or starch, compared to only 9 percent of people without anemia [sources: Gordon, Bowerman ]. And you guessed it -- the most common craving was for ice. Compulsively craving and eating non-food items for a period of at least a month or more is called pica, and when it's ice you crave it's known specifically as pagophagia.