They stated that women who do not take estrogen after removal one or both of their ovaries before menopause are more at risk to have neurological impairment later in life.
One of the function of ovaries is to produce estrogen which is a steroid, sex hormone that primarily influences the female reproductive system's development, maturation, and function. Removal of ovaries can cause a sudden deficiency of that hormone, which in turn affects the brain.
The results of the research show that those women who had one or both ovaries removed before menopause were twice at risk of developing neurological problems compared with those who either keep their ovaries or premenopausal women who remove both ovaries but took estrogen after removal.
Researchers claim that their findings will contribute to a better understanding of the pros and cons of removing the ovaries in young women.
What article are you referring? Keeping 1 ovary in the body does not create problems for a woman. It takes over for both. Please don't make blanket statements like the one you wrote without at least providing supporting documentation.
Actually, many women who had just one ovary removed do experience problems as if both of the ovaries were removed.
For more info:
"Overall, the study found that women who'd had one or both ovaries removed showed about a 50% increase in risk of the later mental problems."