Joan is reported to have said that the "sound of bells" sometimes triggered the voices. Hearing certain sounds can be a trigger for seizures, d'Orsi and Tinuper said.
During a public examination on Feb. 22, 1431, Joan said, "It said to me two or three times a week," referring to how often she heard the voices. Several days later, on March 1, 1431, she is reported to have said, "There is never a day that I do not hear them [the voices]," according to the researchers.
But the frequency with which Joan reported hearing voices is not entirely consistent with the researchers' diagnosis. Other researchers have pointed out that patients with this type of epilepsy have a low frequency of seizures, they wrote. Patients may have seizures infrequently at the beginning, and may also have seizures if they are withdrawing from certain drugs, they wrote. It's unclear if Joan of Arc had taken any substances that may have affected whether she had seizures, they added.
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Joan of Arc also sometimes experienced seizures during sleep. "...I was asleep: the Voice woke me... It awoke me without touching me," Joan was reported to have said during a private examination on March 12, 1431, the researchers wrote. According to d'Orsi and Tinuper, 40 percent of people with this type of epilepsy have seizures during sleep. [Top 10 Spooky Sleep Disorders]
Of course, diagnosing a medical condition in a woman who lived in the 1400s is not exactly easy. Indeed, the researchers noted that "after six hundred years from Joan's death, we reaffirm the impossibility to arrive at a final conclusion."
However, there may be one remaining opportunity to find an answer, and it lies in a missing strand of Joan's hair.
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History suggests that Joan of Arc sealed letters with red wax that had "the imprint of a finger and a hair" in order to prove her identity, the researchers wrote. If historians can locate these letters, scientists may have the opportunity totest the DNA of the hair.
Indeed, in recent studies, scientists have discovered genes that are linked to the specific type of epilepsy that d'Orsi and Tinuper suspect Joan of Arc may have had.
But efforts to find the letters and the hair have come up short so far. "After ten years from our first hypothesis, we are still looking for this hair..." d'Orsi and Tinuper wrote.
Originally published on Live Science.
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