Ultra-detailed brain map shows neurons that encode the meaning of words

Ultra-detailed brain map shows neurons that encode the meaning of words

Nature reports:

By eavesdropping on the brains of living people, scientists have created the highest-resolution map yet of the neurons that encode the meanings of various words. The results hint that, across individuals, the brain uses the same standard categories to classify words — helping us to turn sound into sense.

The study is based on words only in English. But it’s a step along the way to working out how the brain stores words in its language library, says neurosurgeon Ziv Williams at the Massachusetts Institute of Technology in Cambridge. By mapping the overlapping sets of brain cells that respond to various words, he says, “we can try to start building a thesaurus of meaning”.

The work was published today in Nature.

Mapping meaning

The brain area called the auditory cortex processes the sound of a word as it enters the ear. But it is the brain’s prefrontal cortex, a region where higher-order brain activity takes place, that works out a word’s ‘semantic meaning’ — its essence or gist.

Previous research has studied this process by analysing images of blood flow in the brain, which is a proxy for brain activity. This method allowed researchers to map word meaning to small regions of the brain.

But Williams and his colleagues found a unique opportunity to look at how individual neurons encode language in real time. His group recruited ten people about to undergo surgery for epilepsy, each of whom had had electrodes implanted in their brains to determine the source of their seizures. The electrodes allowed the researchers to record activity from around 300 neurons in each person’s prefrontal cortex.

As participants listened to multiple short sentences containing a total of around 450 words, the scientists recorded which neurons fired and when. Williams says that around two or three distinct neurons lit up for each word, although he points out that the team recorded only the activity of a tiny fraction of the prefrontal cortex’s billions of neurons. The researchers then looked at the similarity between the words that activated the same neuronal activity. [Continue reading…]

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