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.
pica (usually uncountable, plural picas) (medicine) A disorder characterized by craving and appetite for non-edible substances, such as ice, clay, chalk, dirt, or sand. 1986, George S Baroff, Mental retardation: nature, cause, and management: The three most common nonfood picas were eating of strings and rags; feces, vomit, and urine; and paper, cigarettes, and soil.