Magneto encephalography (MEG): perspectives of speech areas functional mapping in human subjects

One of the main problems in clinical practice and academic research is how to localize speech zones in the human brain. Two speech areas (Broca and Wernicke areas) that are responsible for language production and for understanding of written and spoken language have been known since the past century. Their location and even hemispheric lateralization have a substantial inter-individual variability, especially in neurosurgery patients. Wada test is one of the most frequently used invasive methodology for speech hemispheric lateralization in neurosurgery patients. However, besides relatively high-risk of Wada test for patient's health, it has its own limitation, e. g. low reliability of Wada-based evidence of verbal memory brain lateralization. Therefore, there is an urgent need for non-invasive, reliable methods of speech zones mapping. The current review summarizes the recent experimental evidence from magnitoencephalographic (MEG) research suggesting that speech areas are included in the speech processing within the first 200 ms after the word onset. The electro-magnetic response to deviant word, mismatch negativity wave with latency of 100—200 ms, can be recorded from auditory cortex within the oddball-paradigm. We provide the arguments that basic features of this brain response, such as its automatic, pre-attentive nature, high signal to noise ratio, source localization at superior temporal sulcus, make it a promising vehicle for non-invasive MEG-based speech areas mapping in neurosurgery.

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