MEG Brain Maps May Help Guide Epilepsy Surgery

Megan Brooks

August 08, 2013

Neuroscientists have used magnetoencephalography (MEG) to produce detailed spatial maps of critical language function, which may help surgeons more accurately plan surgery in patients with epilepsy.

"When carrying out brain surgery it's imperative not only to determine where the areas are to treat but whether the critical regions that carry out higher functions like language and memory will be affected," Ryan D'Arcy, PhD, from the National Research Council (NRC) Institute for Biodiagnostics (Atlantic), Halifax, Nova Scotia, and Simon Fraser University in Burnaby, British Columbia, Canada, said in a statement.

Functional imaging is increasingly being used to provide a noninvasive alternative to intracarotid sodium amobarbital testing (the Wada test), Dr. D'Arcy and colleagues point out in the August issue of the journal Human Brain Mapping.

Although MEG has shown "significant potential" in this regard, the data generated are often reduced to a simplified estimate of laterality, called a laterality index (LI). "Such estimates belie the richness of functional imaging data and consequently limit the potential value," the investigators say.

Their novel approach uses MEG data to compute "complex laterality vectors" and consequently "laterality maps" for a given function, in this case language, in healthy adults and in people with epilepsy.

The language-related laterality map they generated matched closely with the known functional anatomy that supports language.

In addition, they say their maps provided "more specific and clinically relevant information about activation magnitude and location, when compared with typical LI scores for both healthy controls and patients." This should translate into improved capabilities for presurgical planning and for evaluating potential clinical outcomes, they say.

Preliminary Study

Roberto F. Galán, PhD, assistant professor of neuroscience at Case Western Reserve University School of Medicine in Cleveland, Ohio, and a trained electrophysiologist, who wasn't involved in the study, cautioned that the results are preliminary.

"The main finding of the study is that they can measure the asymmetric activation of brain regions in both hemispheres associated with language function in a noninvasive way," he told Medscape Medical News.

"They also use this measure of asymmetric brain activity in epileptic patients but they don't explain why an asymmetric activation of brain regions was expected to be different in epilepsy. In fact, there are no dramatic differences relative to control individuals," Dr. Galán noted.

"This is clearly a pilot study that is still far from clinical application, at least in the context of epilepsy. The method, however, may be useful in fundamental research to investigate the asymmetric activation of the brain hemispheres in language and other cognitive functions," Dr. Galán said.

Dr. Galán has also studied brain imaging with MEG. As previously reported by Medscape Medical News, he found that analyzing brain activity patterns in children may allow confirmation of an autism spectrum disorder (ASD) diagnosis with high accuracy.

His study showed that use of MEG to measure functional connectivity (the communication from 1 region of the brain to the other) and background noise in 19 children provided an accuracy rate of up to 94% in differentiating those with and those without an ASD.

The current study was supported by grants from the National Research Council of Canada, The Atlantic Innovation Fund, and The Natural Sciences and Engineering Research Council. The authors and Dr. Galán have disclosed no relevant financial relationships.

Hum Brain Mapp. 2013;34:1749-1760. Abstract


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