restricted access Sex Differences in Sensory Functions
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SEX DIFFERENCES IN SENSORY FUNCTIONS WEIERT VELLE* Introduction The senses mediating external stimuli represent the only bridges between ourselves and the reality surrounding us. A question of fundamental significance is to what extent our senses give us correct information about the real world. Most neurophysiologists probably share the view expressed by their colleague Mountcastle [1] in his vivid statement, Each of us believes himself to live directly within the world that surrounds him, to sense its objects and events precisely, to live in real and current time. I assert that these are perceptual illusions, for each of us confronts the world from a brain linked to what is "out there" by a few million fragile sensory nerve fibres. These are our only information channels, our lifelines to reality. These sensory nerve fibres are not high-fidelity recorders, for they accentuate certain stimulus features, neglect others. The central neuron is a story-teller with regard to the afferent nerve fibres; and he is never completely trustworthy, allowing distortions of quality and measure, within a strained but isomorphic spatial relation between "outside" and "inside." Sensation is an abstraction, not a replication, of the real world. Since our behaviour is to a large extent influenced by external stimuli, it would seem to be of crucial importance that each of us perceive such stimuli in much the same way. Medical literature is, however, filled with examples of altered behaviour caused by aberrant sensory functions— many examples of which can also be observed in everyday life by one without any special professional skills. Perception of reality is, of course, also dependent on the functional state of the sensory organs. A colourblind person experiences reality differently from a person with normal colour vision. So far, there will probably be general agreement. ?Department of Physiology, Norwegian College of Veterinary Medicine, P.O. Box 8146 DEP, Oslo, Norway.© 1987 by The University of Chicago. AU rights reserved. 0031-5982/87/3004-0554$01.00 490 I Weiert Velie ¦ Sex Differences in Sensory Functions One may, however, go one step further and ask whether even differences in sensory function within the normal range may have behavioural consequences. This question has special relevance in relation to sex differences in behaviour. In current discussion about the relative importance of environmental and genetic factors as determinants of behaviour , very little attention has been paid to this aspect. Sex differences in sensory function, and for different senses, have been reported by various authors in variousjournals, but an overview of the field as a whole seems to be lacking. The aim of this article is to bridge this gap by reviewing the literature concerning the taste, smell, hearing, vision, and cutaneous senses. The review is followed by a discussion of the validity of the published data and of possible causes underlying sex differences. Finally, the functional significance of sex differences in sensory functions during human evolution is briefly discussed . Taste The four taste categories, sweet, sour, salty, and bitter, are each represented by specific taste receptors localized in different areas of the tongue. Interpretation of published data on sex differences in the function of taste is difficult. Various authors have used different test substances, and the methods of application of the substances have also varied. Nevertheless , some interesting sex differences have been observed. In humans three different aspects have been studied: sensitivity (thresholds), ability to taste, and consistency of response. Animal experiments have mainly been concerned with taste preferences. Sensitivity.—Taste sensitivity in relation to age in both men and women has been tested by the use of solutions of sucrose, citric acid, sodium chloride, and quinine sulphate as representing sweet, sour, salty, or bitter taste, respectively [2]. The study comprised 280 subjects, with 20 ofeach sex in each age group, from the first to the seventh decade, none of whom had indicated any prior evidence of disturbance of the taste sense. The stimulus was administered with a probe moistened with the solution and applied on both sides of the tongue at the site of predilection for each taste category. The sensitivity for each test substance decreased with age from the first to the seventh decade in both men and women, the difference between...