A study found that extremely premature infants who were fed breast milk in the hospital did better on tests of mental development later in life than others fed only formula(人工乳). The more breast milk(母乳)the babies consumed, the better they did on the tests. Researchers believe this is because ingredients in breast milk, particularly fatty acids, aid in brain development. Breast milk had no effect on rates of cerebral palsy(脳性麻痺), blindness or hearing problems.