Abstracts

RATIONALE: Surgical treatment of epilepsy often requires determination of the cerebral hemisphere mediating language. Intracarotid amytal injection (Wada test) is the current standard for language lateralization but is invasive. Positron emission tomography and functional MRI have been used as alternatives, but these methods are expensive and complex. Near-infrared spectroscopy (NIRS) uses transcranial reflectance spectroscopy to measure oxygenated hemoglobin, deoxygenated hemoglobin, and total hemoglobin concentrations with a temporal resolution of 0.1 second. In this pilot study, we used NIRS to non-invasively measure changes in bilateral inferior frontal blood flow during a word generation task in post surgical epileptic patients and healthy volunteers in an effort to lateralize language centers.
METHODS: Cerebral blood flow was measured by using a Hitachi Medical Corporation [reg] NIR Optical Topography System (Model ETG 100). Two separate optical topography probes, each containing five semiconductor laser light sources (780 and 830 nm wavelengths; radiated power [lt] 5.0 mW/mm2) and four avalanche photodiode detectors were arranged in an alternating fashion to form two three by three grids that were placed on the scalp anterior and superior to the ears. Six epileptic patients who had previously undergone Wada testing and seven healthy right-handed/right footed individuals underwent NIRS during a word generation paradigm. Specifically, they performed ten repetitions of the task of writing lists of words beginning with a randomly presented letter for either 17 or 30 seconds followed by either 60 or 30 seconds of a resting task, consisting of copying a line drawing of a city scene. Changes in infrared light absorption were measured bilaterally in real time and regional blood volume variability between the two sides was extrapolated from this data.
RESULTS: Inferior frontal total hemoglobin concentration increases agreed with Wada test results in five patients with left-sided language dominance and one with right-sided dominance. In the healthy subjects, NIRS revealed increases in inferior frontal total hemoglobin concentrations congruent with language dominance as predicted by handedness/footedness in all 7 individuals.
CONCLUSIONS: NIRS has advantages over other methods used to lateralize language dominance. The device is portable, simple to use, and testing is complete in 30 minutes. The probes are non-invasive, and involve minimal discomfort for the patient. The word generation paradigm is simple and is appropriate for mildly developmentally delayed individuals who cannot adequately perform in the Wada test. NIRS may be a feasible, simple, cost-effective, non-invasive method for lateralizing language.
Support: The National EpiFellows Foundation.