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Week 24/2011: Brain waves indicate the origin of speech

Before this possibility, locating the origins of speech in the brain not only caused discomfort to the subject but was also potentially dangerous. It is now hoped that magnetoencephalography (MEG) measurement will considerably improve research.

At the moment, the Wada test is the most frequently used test where one cerebral hemisphere is paralysed using an anaesthetic, and then the patient is requested to read numbers out loud, for example. Based on the level of success, it is determined whether there are speech areas in the hemisphere. The test must always be conducted for both hemispheres because speech areas may exist in both. The MEG device deployed measures in the cerebral magnetic fields outside the skull. The magnetic fields result from electric fields on which the operations of the brain cells are based.

In addition to MEG measurement being safe for the subjects, it seems that skull-external measurement is no less accurate than the Wada test. It is very important to accurately locate speech areas because it allows for brain surgery planning, for example, so that the patient's faculty of speech will suffer as little as possible. By means of the mapping, it can also be predicted what kind of rehabilitation the patient will need after surgery. Since MEG measurement is much more pleasant for the patient than the Wada test, it is also often suitable for those on whom the Wada test cannot be conducted, such as small children.

The results obtained through MEG measurement are very similar to those obtained using the methods most frequently used at present. In the future, MEG measurement may also provide more accurate and extensive results than the Wada test, especially when combined with other kinds of brain research.

"The results obtained through a time frequency analysis of MEG data seem to be promising, but more extensive research is yet required at the individual level, combined with structural brain imaging, for example, says Onerva Korhonen, who has studied skull-external location of speech areas at the Aalto University.

Korhonen completed her B.Sc. thesis focusing on methods for using MEG data to map the nerve system mechanisms in speech production at the Neuroscience Center of the University of Helsinki on Matias Palva's research team and at the BioMag laboratory.

Text: Milja Heikkinen
Picture: Juha Montonen BioMag laboratory / Helsinki University Central Hospital
Translation: AAC Global

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