“Two central mysteries of human brain function are addressed in this study: one, the way in which higher cognitive processes such as language are implemented in the brain and, two, the nature of what is perhaps the best-known region of the cerebral cortex, called Broca’s area,” said first author Ned T. Sahin, PhD, post-doctoral fellow in the UCSD Department of Radiology and Harvard University Department of Psychology.

The study demonstrates that a small piece of the brain can compute three different things at different times – within a quarter of a second – and shows that Broca’s area doesn’t just do one thing when processing language. The discoveries came through the researchers’ use of a rare procedure in which electrodes were placed in the brains of patients. The technique allowed surgeons to know which small region of the brain to remove to alleviate their seizures, while sparing the healthy regions necessary for language. Recordings for research purposes were then made while the patients were awake and responsive. The procedure, called Intra-Cranial Electrophysiology (ICE), allowed the researchers to resolve brain activity related to language with spatial accuracy down to the millimeter and temporal accuracy down to the millisecond.

This is the first experiment to use ICE to document how the human brain computes grammar and produces words.

Because complex language is unique to humans, it has been difficult to investigate its neural mechanisms. Brain-imaging methods such as functional MRI are generally all that are possible to use in humans, but they blur the activity of thousands or millions of neurons over long periods of time. Consequently, scientists have been unable to determine in detail whether the mechanisms used by linguistic or computational models to produce grammatically correct speech correspond to the mechanisms that the brain actually uses.