Babies who had a lullaby played to them regularly while still in the womb recognised the song months after birth, a study has found. The researchers had 10 expectant mothers play Twinkle Twinkle Little Star loudly multiple times each week throughout their last trimester of pregnancy. A few days after birth, they took electroencephalogram, or EEG, recordings of each newborn's brain by using 12 electrodes scattered over different regions of the head. Upon hearing the lullaby again, they had significantly larger brain responses than a control group of newborns who had not been exposed to the song. The experiment was repeated after four months with similar results. Study co-author and University of Helsinki psychologist Minna Huotilainen refers to this phenomenon as "preconscious learning". The babies have no awareness of it - no "Oh, that old song from my intrauterine days" - but somehow their brains can still pick up on the fact that they have heard it before. "They recognise the memory, and their brains react to it," said study co-author Eino Partanen, also a University of Helsinki psychologist. "But do we mean memory like how we have in adults? No. This is more like familiarity." Also, the scientists found that the more times a mother played the recording for her unborn child, the stronger the electrical signal from the baby's brain would be. When the researchers played a modified version of Twinkle Twinkle Little Star , the babies seemed to notice when that was amiss. The EEG was fast enough to catch note-by-note neural responses, and when a wrong note was played, their brains would react differently. "It is a matter of noticing a difference between what you hear and what you should be hearing," Partanen said. "Memory plays a part in that." The study was published online on Wednesday in the journal PLOS One . An early study on auditory fetal learning - titled Fetal 'Soap' Addiction - looked at mothers who had regularly watched a certain soap opera while pregnant. Several days after birth, their babies appeared to recognise the soap's theme song whenever it came on. They would stop wailing and instead focus rapt attention toward the television. Although many anecdotal or behavioural studies have been done, Partanen and his colleagues wanted to back up the vague speculation of fetal learning with quantitative electrical markers of the brain at work. Key structural parts of the ears develop throughout the first 20 weeks of gestation.