Seminar Series

Neuronal dynamics underlying language comprehension

During language comprehension, incoming sounds or orthographic patterns trigger a cascade of memory retrieval operations that make available the necessary ingredients for understanding the message. Once available, these different ingredients, which include the phonologic, syntactic and semantic properties of lexical items, have to be integrated (unified) to yield a coherent interpretation of the utterance. Thus, two different cognitive processes, namely memory retrieval operations and unification operations, play a crucial role during language comprehension. Neuroimaging studies using PET and fMRI have revealed that a large number of widely distributed brain areas is involved in processing these different types of information. However, in order to capture the fast dynamics of the brain’s language network, the information obtained from PET and fMRI studies needs to be complemented with information derived from imaging methods such as EEG and MEG, that record neuronal activity on a millisecond time scale. Changes in EEG or MEG power (i.e., squared amplitude) in a particular frequency band reflect synchrony changes in spatially confined brain areas. This indexes integration of information within a node of the network. On the other hand, changes in phase coherence (i.e., the extent to which oscillatory signals measured at different sensors have a constant phase difference) are thought to reflect changes in synchrony between spatially distant cortical areas. Coherence changes thus index the integration of information between different nodes of the network. Power and coherence changes in the EEG or MEG during language comprehension tasks have been observed in three different frequency bands: theta (4-7 Hz), gamma (above 30 Hz), and lower beta (13-18 Hz). The effects can roughly be subdivided into effects related to mnemonic aspects of language comprehension, and effects related to unification. In the presentation I will address the above issues, and give an overview of the existing data on oscillatory brain dynamics during language comprehension