GENDER DIFFERENCES IN CHEMOSENSORY FUNCTION

Undergraduate

Abstract 

This thesis consists of two studies, in which gender differences in nasal chemosensory function are investigated. The first study assesses odor identification ability in a populationbased sample, varying from 45 to 90 yrs, screened for cognitive impairment and severe olfactory dysfunction. Results show that women are generally better than men at identifying odors, but there is no significant interaction of gender by age. Although odor identification is influenced by semantic memory and cognitive speed, these cognitive factors are unlikely to cause the observed gender difference in odor identification. The second study investigates chemosensory perception in men and women by assessing eventrelated brain potentials, and perceptual ratings for an odorant, which varies in concentration and olfactory/irritating properties. The results display a generally larger cortical response in women than in men, beginning from about 350 ms after stimulus onset. Women report higher perceived intensity and unpleasantness at the highest stimulus concentration, and a steeper psychophysical function, than do men. The results indicate that stronger cortical responses of nasal chemosensory stimuli provide a neural basis for stronger supra-threshold perception in women than in men, which might enhance odor identification performance. The nature and causes of these gender-differences in nasal chemosensory function are discussed. 

 

INTRODUCTION

 

“…a complete, comprehensive, understanding of odor… may not seem a profound enough problem to dominate all the life sciences, but it contains, piece by piece, all the mysteries.”

                                                                                        -Lewis Thomas

 

Although not often recognized, the ability to perceive smelling, tasting, and irritating chemicals is very important in our everyday lives. In order to detect health-hazardous chemicals in food and air, we use mainly our nasal chemoreceptors, which mediate information about the chemical environment through the olfactory and trigeminal nerves. By powerful food aversion learning, the chemical senses keep us from ingesting food items that has previously been associated with illness (Jacobsen, Bovbjerg, Schwartz, Andrykowski, Futterman, Gilewski, et al., 1993). In a modern society, the abilities to detect, recognize, and discriminate odors are fundamental and important tasks in food behaviour and nutrition, and the chemical senses influence our perceived life quality and psychological well-being (Hummel & Nordin, 2005). Some researchers emphasize the social and sexual roles of the chemical senses (Gower & Rupareila, 1993). Individual differences in olfactory abilities are pronounced, and depend on various biological, cognitive and social factors. Differences between men and women have been studied in a variety of settings. However, there seems to be no definite conclusion on the influence of gender on olfactory abilities (Brand & Millot, 2001). 

     The present work concerns nasal chemosensory perception and cognition in men and women. In two studies, possible gender differences in various aspects of chemosensory function are investigated. The first study (Larsson, Nilsson, Olofsson & Nordin, 2004) concerns the ability to identify household odors in a four-alternative forced-choice task. Gender differences in this task are assessed by results from a population-based investigation of 1906 healthy individuals, divided in five age cohorts of the adult life-span (45-90 yrs). A possible interaction between gender and age, as well as cognitive factors influencing odor identification ability are also assessed. In the second study (Olofsson & Nordin, 2004) gender differences in odor perception are addressed by a combined neurophysiological and perceptual assessment of healthy young adults. A background and a review of relevant literature is provided in the first section of this work: This includes an introduction to nasal chemosensory physiology and common testing procedures to assess nasal chemosensory function. A brief review over gender differences in perception and cognition, as well as a description of the event-related potential (ERP) technique used in Study 2 is provided. The present studies are presented, and the results are discussed in the context of previous research. The prospects and the pitfalls of studying gender differences in chemosensory function are discussed from a methodological and a clinical perspective. The reader is referred to the two original articles for a more detailed description of the present studies.