Researchers from the University of South Carolina Arnold School of Public Health, the University of Maryland, and the University of Massachusetts have examined how brain activity unfolds across the duration of sentence comprehension on a millisecond-by-millisecond basis to build the complex structures that allow for the expression of novel meanings in language. The study, which was published in Human Brain Mapping, was led by University of South Carolina Communication Sciences and Disorders assistant professor Dr. William Matchin.
Previous research has identified key brain regions involved in language. However, little is known about the time course of activities in these regions. Commonly used methods like functional magnetic resonance imaging (fMRI), which measures brain activity by detecting changes associated with blood flow, provide great detail into the specific brain structures. However, fMRI does not provide a picture of the timing of activation in brain areas. These studies have been unable to clearly distinguish the specific contributions of each brain area because of this limited timing information.
In the present study, Dr. Matchin and his team performed a magnetoencephalography (MEG) experiment to provide this timing information, combining MEG data with fMRI data to provide insights into both the location and timing of brain activity. MEG, like electroencephalography (EEG), measures brain waves, but unlike electrical waves, magnetic waves pass through the human skull without distortion. This allows researchers to link the high spatial resolution of fMRI with the improved spatial resolution of MEG more accurately than with EEG.
[Photo: Dr. William Matchin]
Using these combined techniques, the researchers were able to distinguish the functions of different brain regions involved in language using the timing information provided by MEG. In particular, they showed that the posterior temporal lobe plays a key role in processing the structure of sentences, while the anterior temporal lobe and the temporo-parietal junction play distinct key roles in processing the content or meaning of sentences. These regions work together to allow people to create and understand novel sentences.
The authors’ fMRI-guided MEG investigation therefore helps identify distinct structural and meaningful aspects of sentence comprehension in the brain in both spatial and temporal dimensions.