Functional MRI in pre-surgical language mapping in epilepsy patients

by Motshidisi Matela

Can you take quick guess which neurological disease is most prevalent in the world? If you guessed epilepsy, you are correct. Epilepsy is a condition in which one experiences recurrent and unprovoked seizures, it affects 50 million people worldwide both males and females of all races, ethnic backgrounds, and ages. Epileptic patients must take medication to help with their seizures, however 30 % of these patients develop drug resistant epilepsy (DRE) and only 60% of DRE patients respond to surgery. Many people can unfortunately suffer from cognition impairments because of epilepsy.

While surgery seemed to be the light at the end of the tunnel for patients with DRE, it seems the light might not last for long as many patients develop speech impairments because of resections performed during surgery to remove the epileptic regions of the brain.  To operate effectively, areas of the brain that are necessary for language formation and comprehension must be identified so that they are spared during surgery. This can be accomplished by with Functional Magnetic Resonance Imaging (FMRI). This technique uses blood oxygen dependent levels (BOLD) contrast to measure oxygen changes within the brain in response to different tasks.

UCT researchers had then set out to investigate how fMRI could be used as an effective method for preoperative language mapping. This can help maximize resections of epileptic regions while minimizing impairments.

To see which brain regions are responsible for language, Ives-Deliperi et al performed blocked tasks in which patients were subjected to a stimulus at active to activate the brain regions, while at rest no stimulus was given.

Fig. 1. Functional mapping blocked paradigm.

The authors used different methods to map areas that responsible for comprehension of language and those responsible for expressive of language.

The results were good areas that are involved in both receptive and expressive language were not only localized meaning which part of the brain region is responsible for the activity, but also lateralized meaning can be seen in which brain hemisphere are these regions located. The bold signal increased with activation of these regions.

Fig. 3. BOLD signal increase produced in the group analysis of the verb generation task showing activation in left posterior inferior frontal gyrus (Broca’s area) and left superior temporal gyrus (Wernicke’s area).

Fig. 4. BOLD signal increases produced in the group analysis of the passive listening task in the superior temporal lobes bilaterally (Wernicke’s area).

The preservation of neurological function in epileptic patients during surgery is key to successful treatment. The success of this technique may have positive treatment implications for other neurological diseases as well, including traumatic brain injury and brain infection diseases. In simple words performing fMRI before surgery might keep the light at the end of the tunnel for patients with DRE.

References

1.            Ives-Deliperi, V. L.;  Butler, J. T.; Meintjes, E. M., Functional MRI language mapping in pre-surgical epilepsy patients: findings from a series of patients in the Epilepsy Unit at Mediclinic Constantiaberg. South African medical journal = Suid-Afrikaanse tydskrif vir geneeskunde 2013, 103 (8), 563-7.

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