“I want to know what happens. I want to see the results of this experiment before I become demented.”

She had a history of stroke and, it was reported, had become “demented” in her later years — mostly in the form of memory loss and confusion.

Patients with I.B.D. developed dementia at an average age about seven years younger than that of the controls, and the longer they had I.B.D., the more likely they were to become demented.

Even if I do not become demented, I shall likely decline over the next eight years.

“You can become demented and lose coordination, and some of it is reversible, some of it isn’t,” Stern said.