A study reviewing the health of thousands of women decades after undergoing surgical ovary(卵巣)removal, or oophorectomy(卵巣摘出術), indicates that ovary excision(摘出)prior to menopause(閉経)is linked to increased risk of dementia(痴呆)and Parkinson's disease. Experts theorize that estrogen, a female sex hormone produced by the ovaries, plays some role in protecting the brain from toxins that lead to nerve cell death. Estrogen replacement therapy was found to effectively reduce the risk of cognitive(認識の)decline following oophorectomy.