At the end of the 19th century, scientists did a lot of research about dyslexia and found some of the reasons that people are dyslexic. A professor who did research in the 1980s and 1990s looked at the brains of dyslexic people who had died. He found that some parts of the brain were not connected very well, and that this happened during the fourth month of pregnancy. This problem has a big effect on the left half of the brain. The newest research shows that three genes are the reason for dyslexia.