Thiamin increases circulation and assists in the production of hydrochloric acid, blood formation, and carbohydrate metabolism. Thiamin has a direct correlation to the production of energy, and is needed for normal muscle tone of vital internal organs. The classic symptom of a thiamin deficiency is the disease beriberi in which a person may experience reduced function of the lower extremities, nerve damage, heart problems, or brain damage. For example, Korsakoff's psychosis is characterized by the inability to form new memories, the poorly organized retrieval of old memories, apathy and emotional blandness. The treatment of these patients with thiamin often results in significant improvement. In other studies involving female subjects, marginal thiamin deficiency has been shown to result in mood swings and irritability. Treatment of these patients with thiamin, again resulted in an improved condition.