OLFACTION IN EPILEPSY

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DESCRIPTION: (Adapted from the Investigator's Abstract) The primary olfactory cortex is compromised in temporal lobe epilepsy (TLE) and by surgical treatment for intractable forms of this disease (e.g., temporal lobe resection or TLR). Although a number of studies have examined olfactory function in both TLE and TLR patients, the results are far from conclusive. In the case of threshold measures, for example, some studies report that TLE decreases sensitivity, other report that TLE increases sensitivity, and still others find no influences of TLE on sensitivity at all. The same is true for TLR. Unfortunately, olfactory tests of unknown or questionable reliability have typically been employed, bilateral testing has been the rule rather than the exception (bilateral test scores reflect the better functioning side of the nose), too few subjects have been evaluated, and the amount or location of brain tissue damaged by TLE has not been quantified. Furthermore, with only one exception, pre-/post TLR designs have not been employed. Thus, very basic questions regarding the influence of TLE and TLR on the ability to smell remain unanswered. For example, are some olfactory abilities (e.g., detection sensitivity), but not others (e.g., odor identification), largely insensitive to central temporal lobe lesions? Is olfactory function altered bilaterally or only on the side of the epileptic foci? To what degree is TLE-related olfactory loss, if present, further attenuated by TLR? Are psychophysical olfactory losses mirrored by changes in EEG activity induced by odorous stimuli? The proposed research is designed to provide definitive answers to these and other basic questions, and is driven by the hypothesis that complex olfactory tasks are more likely influenced by temporal lobe lesions than less complex olfactory tasks. In this work, each side of the nose will be tested separately and comprehensively in a comparatively large group of TLE patients before and after TLR. Quantitative MRI will be employed to assess the relationship, if any, between the test measures and the volume and location of damaged or resected tissue. In addition to providing a better understanding of the influences of TLE and TLR on human olfactory function, this work may lead to the development of a simple and inexpensive non-invasive means for better establishing TLE seizure loci.