New Data Suggests Abnormal Activation of Language Cortex in Patients with Chronic Epilepsy

Today, at the 58th annual AES conference in New Orleans Joshua Breier, (neuropsychologist with the Comprehensive Epilepsy Program at the University of Texas Health Science Center at Houston) presented his most recent findings from a retrospective study he and several colleagues conducted exploring abnormal activation of language cortex in patients with chronic seizures and academic achievement deficit. In this study, Breier et. al used magnetoencephalography (MEG) to examine the relation of the status of the brain mechanisms for language function to reading ability in patients with chronic intractable epilepsy. They also explored the manner in which seizure variables such as duration of seizure and age of onset affected these brain mechanisms.

What is MEG?

MEG (magnetoencephalography), which is related to electroencephalography (EEG) measures the magnetic energy generated by the electrical discharge in relatively large collections of neurons within the brain. Variations in the strength of this energy that occur in association with epileptiform discharges or task performance (e.g. listening to words) can be recorded at the scalp. The source of this magnetic energy within the brain can be reliably determined and used to localize the source of the epileptiform brain activity, which may be the source of seizures. It can also be used to provide images showing both the location and timing of activity associated with various aspects of language function, including receptive language.

How Was the Study Designed?

MEG data was collected while 83 patients of varying age and IQ level performed a continuous recognition memory task for concrete nouns presented auditorily. Patients raised either the right or left index finger for a repeated stimulus. All patients underwent pre-surgical evaluation, including 24-hour VEEG, MRI, and neuropsychological testing. Patients were identified as reading deficient if the reading score on the Wide Range Achievement Test (a standard reading achievement screening test) was 25% ile.

“The 83 patients who participated in this retrospective study had all been pre-surgically evaluated at the Comprehensive Epilepsy Program at the University of Texas Health Science Center at Houston. They all underwent mapping of language cortex between 1997 and 2002 using magnetoencephalography,” said Breier.

Results

Among patients with left hemisphere seizure onset (n=58) those with reading achievement deficits (n=18) exhibited a greater degree of bilateral activation during the recognition memory task as indicated by MEG results. Bilateral activation is the equal activation of both the right and left hemispheres. The significance of this finding according to Breier is, “Most individuals without neurological dysfunction show predominantly left hemisphere activation during language tasks. When the left and right hemisphere are equally activated this is considered bilateral activation, an unusual profile of activity for a language imaging study.” Results from the study also indicate that an individual is more likely to have reading problems if they had left hemisphere seizure onset and either an earlier age at seizure onset or a longer duration of seizure disorder.

Implications of Study

In terms of the implications of the findings from this study Breier said, “We know that people with chronic seizures are at a greater risk for academic problems such as reading difficulty than individuals with no neurological disorder. While there are potentially many reasons for this increased risk, the current study suggests that a specific neurophysiological abnormality in areas associated with language function may be present in patients with seizures of left temporal lobe origin.”

He believes the next step in furthering our understanding of neurophysiological abnormalities in the areas that process language in this group is to, “undertake a longitudinal study in children with new onset seizures that are followed across a significant period of time to document the relation between changes in cognitive abilities and brain function. It would also be useful to study the effects of various factors such as etiology, seizure type, medications, and academic experience on this relation.”

The abstract of this study is published in Epilepsia, Vol. 45, Supplement 7, p. 297.