Hidden truth about the semantic functions of the brain

Alex Huth’s paper, “Semantic information in natural narrative speech is represented in complex maps that tile human cerebral cortex” has been published in Nature on April 27, 2016. The scientists of the University of California, Berkeley conducted a study to map how the brain represents the meaning of language.

As they wanted to map the full range of semantic concepts in a single study they used natural, narrative story stimuli. This made it possible to construct a semantic map for each individual, which shows which brain areas respond to words with similar meaning. The research proves that language is not restricted to certain sections, rather activities are all across the brain and in both hemispheres. By monitoring the blood flood in different parts of the brain the scientists worked out which places were responding to the meaning of the words. They found that different bits of the brain responded to different kinds of words and concepts. Moreover, they also found that the responses in the right cerebral hemisphere are about as large and as varied as responses in the left hemisphere. This challenges the current dogma holding that language involves only the left hemisphere.

The study found that different individuals have remarkably similar semantic maps. For example, in the lateral parietal cortex, all seven of our subjects showed an area selective for words related to people. While there are small differences in the exact anatomical location of these semantic areas across individuals, their relative positions are very similar.

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In future studies, they hope to study how experience, native language, and culture may relate to more fine-grained individual differences in these maps. It is possible that the semantic maps would vary between individuals that grew up in very different cultures, who have a different native language or who speak more than one language.

The work also has implications for studying how people recover from brain injuries including stroke, which may affect language related areas. For example, unaffected semantic areas may provide compensatory mechanisms for the brain to rewire after injury. Future studies will clarify whether and how these maps change in language disorders such as dyslexia or delayed language learning.

Lusine Sargsyan

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