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Seizure focus affects regional language networks assessed by fMRI

M. M. Berl, PhD, L. M. Balsamo, PhD, B. Xu, PhD, E. N. Moore, BS, S. L. Weinstein, MD, J. A. Conry, MD, P. L. Pearl, MD, B. C. Sachs, MA, C. B. Grandin, MD, PhD, C. Frattali, PhD, F. J. Ritter, MD, S. Sato, MD, W. H. Theodore, MD and W. D. Gaillard, MD

From the Department of Neurosciences (Drs. Berl, Balsamo, Weinstein, Conry, Pearl, and Gaillard, E.N. Moore and B.C. Sachs), Children's National Medical Center, George Washington University School of Medicine, Washington, DC; Clinical Epilepsy Section (Drs. Balsamo, Xu, Grandin, Sato, Theodore, and Gaillard), NINDS, and Speech-Language Pathology Section (Dr. Frattali), Rehabilitation Medicine Department, Clinical Center, NIH, Bethesda, MD; Minnesota Epilepsy Group (Dr. Ritter), St. Paul, MN.

Address correspondence and reprint requests to Dr. William Davis Gaillard, Neurology, Children's National Medical Center, 111 Michigan Avenue NW, Washington, DC 20010; e-mail: wgaillar{at}cnmc.org

Objective: To investigate the degree of language dominance in patients with left and right hemisphere seizure foci compared to normal volunteers using a fMRI reading comprehension task.

Methods: Fifty patients with complex partial epilepsy, aged 8 to 56 years and 33 normal volunteers, aged 7 to 34 had fMRI (1.5 T) and neuropsychological testing. Participants silently named an object described by a sentence compared to a visual control. Data were analyzed with region of interest (ROI) analysis based on t maps for inferior frontal gyrus (IFG), midfrontal gyrus (MFG), and Wernicke area (WA). Regional asymmetry indices (AIs) were calculated [(L – R)/(L + R)]; AI >0.20 was deemed left dominant and AI <0.20 as atypical language.

Results: Left hemisphere focus patients had a higher likelihood of atypical language than right hemisphere focus patients (21% vs 0%, ² < 0.002). Left hemisphere focus patients, excluding those with atypical language, had lower regional AI in IFG, MFG, and WA than controls. Right hemisphere focus patients were all left language dominant and had a lower AI than controls in WA and MFG, but not for IFG. AI in MFG and WA were similar between left hemisphere focus/left language patients and right hemisphere focus patients. Patients activated more voxels than healthy volunteers. Lower AIs were attributable to greater activation in right homologous regions. Less activation in the right-side WA correlated with better verbal memory performance in right focus/left hemisphere-dominant patients, whereas less strongly lateralized activation in IFG correlated better with Verbal IQ in left focus/left hemisphere-dominant patients.

Conclusions: Patients had lower asymmetry indices than healthy controls, reflecting increased recruitment of homologous right hemisphere areas for language processing. Greater right hemisphere activation may reflect greater cognitive effort in patient populations, the effect of epilepsy, or its treatment. Regional activation patterns reflect adaptive efforts at recruiting more widespread language processing networks that are differentially affected based on hemisphere of seizure focus.

Deceased July 2004.

Supported by NINDS KO8-NS1663, NINDS R01 NS44280, NICHD P30HD40677, the Clinical Epilepsy Section, NINDS, NIH.

Disclosure: The authors report no conflicts of interest.

Received January 21, 2005. Accepted in final form August 9, 2005.

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