Most English dictionaries list words alphabetically, but how do we store them in our head? Finding out could have an unexpected pay-off: being able to tell what someone is thinking from their brain activity.
Although neuroscientists can already do this to a limited extent, the brain鈥檚 internal filing system for words and concepts 鈥� an important step towards accurately reading a person鈥檚 thoughts 鈥� remains murky.
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Now at the University of California, Berkeley, and his team have charted the 鈥渟emantic system鈥� of the human brain. The resulting map reveals that we organise words according to their deeper meaning, in subcategories based around numbers, places, and other common themes.
Previous 鈥渕ind-reading鈥� studies have shown that certain parts of the brain respond to particular words. Gallant鈥檚 own lab had already found that the brain sorts visual information by meaningful categories like animals or buildings.
In their latest experiment, the team wanted to see if they could build a more complete map of meaning across the cerebral cortex, the folded outer layer of grey matter.
Story time
To do this, they asked seven people to listen to two hours of The Moth Radio Hour, a show which features individuals telling stories. As this happened, they used an fMRI scanner to log changes in blood oxygen levels across the brain 鈥� a sign of neural activity.
The team then compared the meanings of the words in the show against the activity in small subregions of the brain.聽They identified 12 categories of words 鈥� concepts such as time, location, emotion or social relevance 鈥� that seemed to activate more than 100 brain regions in different ways.
Other categories included visual words (for example 鈥測ellow鈥�), work concepts (鈥渕eetings鈥�), tactile words (鈥渇ingers鈥�), and abstract ideas (鈥渘ature鈥�).
The team then used software to plot clustering data from six people on a single brain map, pictured below. It charts a complex pattern of activity across more than 100 areas spanning both brain hemispheres. This is a surprise as the brain鈥檚 left side is generally considered to be responsible for language.
The map suggests that patterns of word meaning are consistent between different people鈥檚 brains, but the team say this might be because they studied a small number of people with a culturally similar upbringing and education.
With a map like this, the team also suggest it may be possible to build a 鈥済eneral-purpose language decoder鈥�, a device that can infer what someone hears or says using fMRI data alone.
杏吧原创s have long suspected that words are organised into clouds of meaning in the brain, says , a neurologist at Imperial College London. 鈥淭he results won鈥檛 really surprise anybody,鈥� he says.
But by studying people while they listened to stories, rather than isolated words or sentences, the team has assembled a useful picture of how the brain responds to the kind of language we hear every day, says of Boston University. 鈥淭hey鈥檝e essentially put it all together.鈥�
The map may help us understand language deficits in Alzheimer鈥檚 disease or in aphasia, a condition which can involve using the wrong words or sounds in speech. 鈥淲e鈥檙e struggling with brains that are not this nice and neat and have got damage,鈥� says Kiran. 鈥淭his paper tells us what normal could look like.鈥�
To explore the map, check out the team鈥檚 .
Nature
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