A team of University of California, Berkeley scientists has brought us closer to deciphering people's inner thoughts by creating a "brain dictionary" that shows how the human brain organizes language using numerous colors and dimensions to identify areas that respond to words with similar meanings.

The findings stem from a brain imaging study that recorded brain activity while volunteers listened to stories from a radio show, revealing that at least one-third of the brain's cerebral cortex is involved in processing language. In addition, the study shows that different people have similar maps.

"The similarity in semantic topography across different subjects is really surprising," said Alex Huth, a researcher from UC Berkeley and lead author of the study.

Determining the organization of language in the brain not only poses benefits for helping those with brain damage that cannot speak, but it also brings us closer to decoding the inner dialogue of human thoughts, which could be used to translate what you say into another language as you have a conversation.

"To be able to map out semantic representations at this level of detail is a stunning accomplishment," said Kenneth Whang, a program director in the National Science Foundation's Information and Intelligent Systems division who was not involved in the study. "In addition, they are showing how data-driven computational methods can help us understand the brain at the level of richness and complexity that we associate with human cognitive processes."

The team examined seven native English-speakers and used magnetic resonance imaging (MRI) to scan their brain for hours at a time. As the participants listened to "Moth Radio Hour," the blood flow of each of their brains was measured using MRI. Afterwards, the data was compared to time-coded, phonemic transcriptions - which break down the units of sound that distinguish individual words - of the stories that they were listening to.

The result is a thesaurus-like map that arranges words on the cortices of the hemispheres of the brain, with each word grouped under various headings such as mental, emotional and visual. The map also reveals that most of the human brain contains numerous areas dedicated to describing people and social relations as opposed to abstract concepts.

"Our semantic models are good at predicting responses to language in several big swaths of cortex," Huth said. "But we also get the fine-grained information that tells us what kind of information is represented in each brain area. That's why these maps are so exciting and hold so much potential."

"Although the maps are broadly consistent across individuals, there are also substantial individual differences," said added Jack Gallant, a UC Berkeley neuroscientist and senior author on the study. "We will need to conduct further studies across a larger, more diverse sample of people before we will be able to map these individual differences in detail."

The findings were published in the April 27 issue of Nature.