Chemosensory Event‐Related Potentials in Patients with Temporal Lobe Epilepsy

Abstract

We investigated chemosensory functions in patients with temporal lobe epilepsy (TLE) to discover whether olfactory and trigeminal stimuli applied either ipsilaterally or contralaterally to the epileptic focus are processed differently. Twenty-two patients were investigated, 12 of whom had epilepsy with a focus located in left temporal lobe (LTL). The remaining 10 patients had a right temporal lobe (RTL) focus. Input from the trigeminal system was examined by use of CO2; input from the olfactory system was evaluated with vanillin and hydrogen sulfide as stimuli. Chemosensory function was assessed by evaluation of chemosensory event-related potentials (CSERP) and the patients' verbal reports in an odor identification test. In both groups of patients, prolonged CSERP latencies were noted after stimulation of the left nostril with CO2 as compared with stimulation of the right nostril. In contrast, a different pattern emerged for olfactory stimuli. After right-sided olfactory stimulation, latencies were prolonged in patients with right-sided epileptical foci. Similarly, when the left nostril was stimulated in patients with a left-sided focus, CSERP latencies were prolonged. Thus, neocortical processing of olfactory, but not trigeminally mediated information evidently is affected by functional lesions of the temporal lobe. After olfactory stimulation in patients with a right-sided focus, the distribution of amplitudes was different from normal. Moreover, analyses showed nonoverlapping 95% confidence intervals (CI) for latency N1 when vanillin was applied to the right nostril. These results indicate that RTL may play a different role in processing of olfactory information as compared with LTL.

Olfactory function in patients with and without temporal lobe resection

“…In studies on patients with temporal lobe epilepsy, the results have been unclear as to whether a greater olfactory dysfunction occurs with left or right temporal lobe dysfunction. Support for the dominant role of right temporal lobe in olfactory function comes from studies by Jones-Gotman et al [9], Abraham et al [10], Hummel et al [11], and Zatorre et al [8], while other authors present favorable results for the equivalent relevance of both temporal lobes in olfactory function [12].…”

Intranasal chemosensory function of the trigeminal nerve and aspects of its relation to olfaction

“…Finally, trigeminal activation leads to activity in the insular cortex [68] and the ventral orbital cortex [60,100], with stronger right-sided activity following bilateral stimulation [43,60]. These areas have also been shown to be involved in the processing of olfactory information, and, similarly, research indicates that the right hemisphere is involved to a larger degree in the processing of information about odors [56,63,89,117,118].…”

Influences of temporal lobe epilepsy and temporal lobe resection on olfaction

“…More recently, Jones-Gotman et al [30] and Haehner et al [21] found poorer bilateral odor identification in TLR patients, with poorest performance on the resected side. Other investigators have found no differences between left- and right-side foci and/or resections on bilaterally-administered olfactory tests, including tests of identification, odor memory, and discrimination [9, 18, 19, 27, 29, 42, 49]. In the pre- and post-operative study by Martinez et al [32], odor discrimination was lower only following right-side resection, with improvement occurring on the left side.…”