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NEUROLOGY 2008;71:1621-1627
© 2008 American Academy of Neurology

Evidence for a basal temporal visual language center

Cortical stimulation producing pure alexia

J. Mani, MD, DM, B. Diehl, MD, Z. Piao, MS, S. S. Schuele, MD, MPH, E. LaPresto, MS, P. Liu, MS, D. R. Nair, MD, D. S. Dinner, MD and H. O. Lüders, MD, PhD

From the Department of Neurology (J.M., B.D., Z.P., S.S.S., P.L., D.R.N., D.S.D., H.O.L.) and Brain Tumor Institute (E.L.), Neurosurgery, Cleveland Clinic Foundation, OH.

Address correspondence and reprint requests to Dr. Hans O. Lüders, Professor of Neurology, University Hospitals–Case Medical Center, Department of Neurology, 11100 Euclid Avenue, Cleveland, OH 44106-5040 Hans.Luders{at}uhhospitals.org

Background: Dejerine and Benson and Geschwind postulated disconnection of the dominant angular gyrus from both visual association cortices as the basis for pure alexia, emphasizing disruption of white matter tracts in the dominant temporooccipital region. Recently functional imaging studies provide evidence for direct participation of basal temporal and occipital cortices in the cognitive process of reading. The exact location and function of these areas remain a matter of debate.

Objective: To confirm the participation of the basal temporal region in reading.

Method: Extraoperative electrical stimulation of the dominant hemisphere was performed in three subjects using subdural electrodes, as part of presurgical evaluation for refractory epilepsy.

Results: Pure alexia was reproduced during cortical stimulation of the dominant posterior fusiform and inferior temporal gyri in all three patients. Stimulation resulted in selective reading difficulty with intact auditory comprehension and writing. Reading difficulty involved sentences and words with intact letter by letter reading. Picture naming difficulties were also noted at some electrodes. This region is located posterior to and contiguous with the basal temporal language area (BTLA) where stimulation resulted in global language dysfunction in visual and auditory realms. The location corresponded with the visual word form area described on functional MRI.

Conclusion: These observations support the existence of a visual language area in the dominant fusiform and occipitotemporal gyri, contiguous with basal temporal language area. A portion of visual language area was exclusively involved in lexical processing while the other part of this region processed both lexical and nonlexical symbols.

Abbreviations: BTLA = basal temporal language area; ERP = event-related potential; fMRI = functional MRI; VLA = visual language area; VWFA = visual word form area.

Disclosure: The authors report no disclosures.

Received February 21, 2008. Accepted in final form August 8, 2008.






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