Abstracts

RATIONALE: The importance of temporal lobe structures in human olfactory function has been early recognized since the nineteenth century with the observation that olfactory auras could precede paroxystic seizures in epileptic patients (Jackson and Stewart, 1899). Our study was aimed to determine the influence of unilateral temporal lobe epilepsy (TLE) on olfactory short-term recognition memory and also to examine the related electrophysiological responses recorded in the amygdala.
METHODS: A delayed odor-matching task was performed in 36 right and left TLE patients that were entering a preoperative assessment program for possible surgical treatment which included a stereotactic electro-encephalography (SEEG) procedure. Taking advantage of this procedure, the SEEG activity associated with the odorant stimulations and collected from the amygdala of 18 patients was examined as a function of hemispheric side, matching condition (match vs. mismatch), and stimulus type (sample vs. target).
RESULTS: Behavioral results showed global impairments of the olfactory short-term recognition memory function, evaluated in terms of hit rate, false alarm rate, discrimination measure, and bias measure. An epileptogenic locus side effect was found, with more prominent deficits in left than in right TLE patients. We additionally evidenced a gender effect with higher false alarm scores in male than in female patients, regardless of the side of the epileptogenic focus. Electrophysiological recordings collected from the amygdala demonstrated that odorant stimulations were associated with olfactory evoked potentials (OEPs) consisting of two main components: a positive peak (P1) occurring at 280 ms and a negative one (N2a) at 470 ms. OEPs obtained in response to target (repeated) odorants had reduced peak amplitudes and latencies when compared to OEPs obtained in response to sample (novel) odorants.
CONCLUSIONS: The behavioral results are discussed in terms of psychosocial traits generally observed between the different groups of patients. The electrophysiological data are explained with regards to electrophysiological data obtain in animals and to concepts stemming from cognitive psychology. The reduced peak amplitudes may suggest a mechanism of repetition-suppression, a process assumed to reflect neural activity related to high cognitive processes, such as attention, memory and decision making. Latency modulations, rather appear to be linked to early stages of information processing, and may therefore reflect a facilitation process due to selective attention.
[Supported by: The Region Rh[ocirc]ne-Alpes; The Roudnitska Foundation; The Medical Research Foundation]