Influence of epilepsy and temporal lobe resection on olfactory function.

Olfactory auras accompany some cases of epilepsy. Several aspects of olfactory function, including sensitivity, also may be altered. We reviewed the literature on these topics, as well as studies evaluating the influences of temporal lobe resection and other seizure management procedures on olfactory function. We concluded that: (a) despite several studies, the prevalence of olfactory auras in epilepsy is unknown, with estimates ranging from < 1% to > 30%; (b) epilepsy appears to cause a generalized decrease in olfactory functioning, although increased sensitivity may occur in some epileptic patients at some time in the preictal period; (c) other sensory modalities are also affected by the epileptic process which, in some cases, involve limbic-related temporal lobe structures; (d) many of the olfactory deficits previously attributed to temporal lobe resection actually exist preoperatively; (e) a taste/flavor confusion exists in the reporting of taste auras; (f) unpleasant auras are associated with hyperresponsiveness of neurons, which may explain why most epilepsy-related olfactory auras are described as "bad"; and (g) interesting parallels exist between the effects of the neuroendocrine system on seizure activity and olfactory function.