Hypothyroidism is the condition that results when a disease in the thyroid gland causes a decrease in the production of the thyroid hormone. Hyperthyroidism is a condition in which the thyroid gland produces too much thyroid hormone. These hormonal abnormalities can result in impaired memory. However, only in the congenital form of the disease is the memory loss permanent. In hypothyroidism, occurring even in childhood, and certainly in adult life, any memory loss related to hypothyroidism is completely returned to normal when the patient is treated with a thyroid hormone treatment such as thyroxine. As long as the person takes sufficient thyroxine to maintain them in a normal state, all functions related to thyroid activity are also normal.