Want to improve your vocabulary? The best thing to do is sleep on it
New words are only fully learned when your brain has had a chance to sleep on them. Using functional magnetic resonance imaging (fMRI), scientists at the MRC Cognition and Brain Sciences Unit in Cambridge and the University of York have been able to follow the path the brain takes when a person is trying to learn new words. The images provide the first evidence that two distinct brain systems are involved depending on whether new words have been consolidated overnight or not.
They found that there is a division of labour between the parts of the brain that initially record the sound of a new word and other parts that enable those sounds to be recognised or spoken quickly.
CBSU researcher Dr Matt Davis, the lead author on the paper said: ''Although you can learn new words easily, our research suggests your brain doesn't store that word in the same way as words you already know until the next day. The change between these two stages of learning appears to happen overnight and most likely involves sleep. However, more research is needed to understand what happens during sleep that changes the brain's response.''
In the first experiment, English speakers were asked to learn two sets of fictitious new words on successive days. The words they learnt included 'alcohin', similar to a real word alcohol, and 'caravoth', similar to caravan. While people could learn and remember both sets of new words, it was only words that had been learned on the day before that could be recognised and produced as quickly and efficiently as real words. In combination with previous research, which showed similar changes to new words after twelve hours including time spent asleep, but not after equivalent time spent awake, these results suggest that learning of new words is only complete once overnight consolidation has occurred.
In a second experiment, the volunteers were again trained on two sets of new words, and tested whilst their brain activity was monitored using fMRI. The results showed two different effects of learning, depending on when the words were learned. For words that were entirely unfamiliar, elevated brain activity was seen in a part of the brain associated with new learning: the hippocampus. In comparison brain activity in the cortex—the part of the brain that stores familiar words—only changed for those words that were learnt on the previous day and had been consolidated overnight at the time of scanning.
Professor Gareth Gaskell at the University of York who initiated the research explains: ''This is the first evidence from neuroimaging to show that there are two brain systems involved in different stages of learning spoken words. Putting this together with our previous research, we can see the two systems in operation. The hippocampus learns quickly, but only stores new words in isolation. Later, a slower form of learning takes over in the cortex, and particularly in the temporal lobe. It seems that only a day after initial learning, once overnight sleep has taken place, does the cortex respond to new vocabulary in a word-like way''.