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PubMed1995

Psychological sex differences. Origins through sexual selection.

Men and women clearly differ in some psychological domains. A. H. Eagly (1995) shows that these differences are not artifactual or unstable. Ideally, the next scientific step is to develop a cogent explanatory framework for understanding why the sexes differ in some psychological domains and not in others and for generating accurate predictions about sex differences as yet undiscovered. This article offers a brief outline of an explanatory framework for psychological sex differences--one that is anchored in the new theoretical paradigm of evolutionary psychology. Men and women differ, in this view, in domains in which they have faced different adaptive problems over human evolutionary history. In all other domains, the sexes are predicted to be psychologically similar. Evolutionary psychology jettisons the false dichotomy between biology and environment and provides a powerful metatheory of why sex differences exist, where they exist, and in what contexts they are expressed (D. M. Buss, 1995).

Adaptation, Psychological↗
PubMed2006

Sex differences in predictors of outcome in selected physical therapy interventions for acute low back pain.

STUDY DESIGN: Secondary analysis of pooled data from 3 randomized trials. OBJECTIVE: This study investigated sex differences in response to physical therapy intervention for acute low back pain. BACKGROUND: Sex differences in experimental pain sensitivity have been consistently described in the literature. However, clinical consequences of these sex differences have not been widely reported. METHODS AND MEASURES: Subjects (n=165) were participants in 3 randomized trials of physical therapy interventions from outpatient physical therapy clinics in the general and military communities. Subjects were randomly assigned spinal manipulation with range-of-motion exercise, lumbar stabilization exercise, or directional-preference exercise. Outcomes were measured at 4 weeks through self-report of pain intensity and pain-related disability. Sex differences were investigated with independent t tests (baseline data), 2 x 3 analysis of variance (4-week reductions in pain and pain-related disability), and regression models (predictors of outcome). RESULTS: Men and women had similar reductions of pain intensity (raw mean difference, 0.5; 95% Cl, -1.4 to 0.4) and pain-related disability (raw mean difference, 5.3; 95% CI, -0.1 to 10.7) over 4 weeks. Baseline pain intensity, duration of symptoms, and baseline pain-related disability significantly predicted change in pain intensity for women (r2 = 26%, P < .01). Baseline pain intensity and stabilization exercise predicted change in pain intensity for men (r2 = 33%, P<.01). Baseline pain-related disability, duration of pain, and pain intensity predicted change in disability for women (r2 = 24%, P < .01). Baseline pain-related disability, fear-avoidance beliefs, stabilization exercise, and leg pain predicted change in disability for men (r2 = 32%, P < .01). CONCLUSION: For patients with acute low back pain, men and women had similar physical therapy outcomes for reductions in pain intensity and pain-related disability. However, men and women had different factors that predicted treatment outcome.

Acute Disease↗
PubMed2002

A cross-cultural analysis of the behavior of women and men: implications for the origins of sex differences.

This article evaluates theories of the origins of sex differences in human behavior. It reviews the cross-cultural evidence on the behavior of women and men in nonindustrial societies, especially the activities that contribute to the sex-typed division of labor and patriarchy. To explain the cross-cultural findings, the authors consider social constructionism, evolutionary psychology, and their own biosocial theory. Supporting the biosocial analysis, sex differences derive from the interaction between the physical specialization of the sexes, especially female reproductive capacity, and the economic and social structural aspects of societies. This biosocial approach treats the psychological attributes of women and men as emergent given the evolved characteristics of the sexes, their developmental experiences, and their situated activity in society.

Cross-Cultural Comparison↗
PubMed2002

Sex differences in tuberculosis in Hong Kong.

SETTING: The Hong Kong Tuberculosis and Chest Service, Department of Health, Hong Kong. OBJECTIVE: To examine sex differences in the rate and clinical manifestations of tuberculosis in Hong Kong. DESIGN: Notification rates of tuberculosis during the past five decades were obtained from the Hong Kong Tuberculosis and Chest Service, Department of Health, Hong Kong. In addition, all patients registered with the Chest Service for treatment of tuberculosis in 1996 were studied. RESULTS: The rate of tuberculosis during the past five decades was consistently higher in men than in women, irrespective of age group. The sex difference in rates was highest among those aged over 60 years. In 1996, a higher proportion of women had extra-pulmonary tuberculosis than men; the main site of involvement was the lymph nodes. More women completed treatment at 12 months and fewer women missed treatment appointments. A higher proportion of men had relapse pulmonary disease that was more extensive, a history of previous default from treatment and co-morbid illnesses. CONCLUSION: There are sex differences in the rates and clinical manifestations of tuberculosis in Hong Kong. Study of sex differences is essential for targeting prevention programmes at groups at higher risk.

Adolescent↗
PubMed1996

Sex difference among nonneuronal cells precedes sexually dimorphic neuron growth and survival in an avian song control nucleus.

In zebra finches only males sing, and several song control nuclei contain more neurons in adult males than in females. In the robust nucleus of the archistriatum (RA), this sex difference in neuron number arises because neuron survival is greater in young males than in females. The events initiating this sex difference in neuron survival are not known, but in earlier studies we observed that during sexual differentiation the proliferation and/ or survival of RA cells exhibiting glial morphology is greater in males than in females. Because glia and glia-derived molecules are known to exert trophic effects on developing neurons, we wanted to determine when the sex difference in RA glia develops relative to the sexually dimorphic growth and survival of RA neurons. Male and female zebra finches were injected twice daily with 3[H]thymidine for 2 days beginning either on day 15 or 27. Two days later (day 18 or 30) sections through the RA were processed for autoradiography. Virtually all of the 3[H]thymidine labeled cells within the RA exhibited morphological features characteristic of glia and were not immunoreactive for the neuron-specific antigen, Hu. The number of these 3[H]thymidine labeled cells was measured, as were the number and soma size of RA neurons. Sex differences in RA neuron number and soma size were not evident at day 18, but emerged by day 30. However, at both ages the density of 3[H]thymidine labeled RA cells and their total number/RA neuron were significantly greater in males than in females. No such sexual dimorphism in the density of 3[H]thymidine labeled cells was evident in the archistriatum lateral to the RA, or within the RA of adult birds. These data indicate that sexually dimorphic gliogenesis is an early event in the sexual differentiation of the RA, preceding sex differences in RA neuron growth and survival. The possibility that glia (or glia-derived substances) may contribute to the neurotrophic effects of masculinization within the RA is discussed.

Animals↗
PubMed2006

Sex differences in the hilar mossy cells of the guinea-pig before puberty.

Numerous sex differences have been detected in the morphology of the dentate and hippocampal neurons and hippocampus-dependent memory functions. The aim of the present study was to ascertain whether the mossy cells, an interneuron population forming a recurrent excitatory circuit with the dentate granule cells, are sexually dimorphic. The brains of juvenile (15-16 days old) and peripubescent (45-46 days old) male and female guinea-pigs were Golgi-Cox stained. Mossy cells were sampled from the hilus in the septal third of the dentate gyrus and their dendritic tree and somata were analyzed. The analysis was separately conducted on mossy cells with soma located in the portions of the hilus that face the upper blade (upper hilus) and lower blade (lower hilus), respectively. The mossy cells in the upper hilus were found to be sexually dimorphic in both juvenile and peripubescent animals. At both ages females had a larger dendritic tree than males. This difference was due to a greater mean branch length and, in peripubescent animals, also to a greater number of branches. In juvenile males, the spines on the proximal dendrites (thorny excrescences) had a greater density than in females. No differences in spine density were present in peripubescent animals. Unlike the mossy cells in the upper hilus, the mossy cells in the lower hilus showed very few sex differences in juvenile animals and no differences in peripubescent animals. The few differences favored females, that had more proximal branches and a greater spine density on the distal dendrites than males. The results show that the mossy cells of the guinea-pig are sexually dimorphic prior to puberty. Extending a previous investigation, the present data provide evidence that sex differences are mainly confined to the dentate region corresponding to the upper blade and upper hilus. The observed segregation of the sexual dimorphism in the upper blade/upper hilus suggests that this region might underlie the sexual dimorphism in hippocampus-dependent memory functions.

Age Factors↗
PubMedDate not supplied

Gonadal hormones and sex differences in pain reactivity.

BACKGROUND: Sex differences in the response threshold to painful stimuli and the higher number of chronic pain syndromes in women than in men have prompted a series of studies on lower animals and humans aimed at clarifying the role of gonadal hormones in pain. OBJECTIVE: This article examines the morphologic and functional aspects of gonadal hormone systems and the relations between gonadal hormones and pain circuits, to identify areas deserving of increased attention in elucidating the endocrine mechanisms that contribute to abnormal pain states.

Aging↗
PubMed1999

Sex differences in visuospatial working memory: components of cognitive processing.

Numerous studies have shown that sex differences in visuospatial tasks vary in size and direction depending on the nature of the task, with large differences favoring males on tasks that require transformations in visuospatial working memory. The cognitive processes underlying these differences were investigated using laboratory tasks developed by Dror and Kosslyn (1994). Four cognitive components of visuospatial working memory were assessed--image generation, maintenance, scanning, and transformation--in an attempt to identify the components that would show differential effects for females and males. The image generation task required retrieval of shape information from long-term memory, generation of a visual image in working memory, and utilization of the information about the shape in a decision task. The image maintenance task required only the latter two processes. The information processing demands required by scanning and rotation tasks came from the need to transform the visual image so that it could be used in decision making. Males responded more quickly on all four tasks (ds between .63 and .77), with no between-sex differences in accuracy. We concluded that speed of processing is central to understanding sex differences in visuospatial working memory. We discuss implications of these findings for performance on real-world visuospatial tasks.

Adult↗
PubMed1996

Nature needs nurture: the interaction of hormonal and social influences on the development of behavioral sex differences in rhesus monkeys.

Thirty years of research on early social and hormonal environments and their relationship to the expression of behavioral sex differences in rhesus monkeys are reviewed. These studies demonstrate that whether aggressive and submissive behaviors are sexually dimorphic depends primarily on the social and not the hormonal environment. Early rearing environments without mothers or allowing brief periods of peer interaction produced higher levels of male aggression and female submission. Presenting behavior was expressed more by females than males in environments with high male aggressivity and female submissiveness. No sex differences in presenting occurred in low aggressivity environments, unless monkeys were reared isosexually, when males presented more than females. Rough and tumble play and foot-clasp mounting were consistently exhibited more by males than females across all rearing environments studied, but rearing environment affected the degree of the sex difference. When reared isosexually males displayed less, and females more, foot-clasp mounting than when heterosexually reared. No social environment increased the low frequency of female rough and tumble play. Suppressing neonatal androgen in males did not effect any sexually dimorphic behavior. Prenatal androgen administration to genetic females masculinized many aspects of their juvenile behavior, consistently increasing rough and tumble play and foot-clasp mounting across different social environments. Thus the sexually dimorphic behaviors which showed the smallest variability across social contexts were the most profoundly affected by the prenatal hormonal environment. These studies demonstrate that the expression of consistent juvenile behavioral sex differences results from hormonally induced predispositions to engage in specific patterns of juvenile behavior whose expression is shaped by the specific social environment experienced by the developing monkey.

Animals↗
PubMed2005

Neuroimaging study of sex differences in the neuropathology of cocaine abuse.

BACKGROUND: Female and male substance abusers differ in their disease patterns and clinical outcomes. An important question in addiction neuroscience thus concerns the neural substrates underlying these sex differences. OBJECTIVE: This article aims to examine what is known of the neural mechanisms involved in the sex differences between substance abusers. METHODS: We reviewed neuroimaging studies that addressed sex differences in cerebral perfusion deficits after chronic cocaine use and in regional brain activation during pharmacologic challenge and cue-induced craving. We also present results from a preliminary study in which cocaine-dependent men and women participated in script-guided imagery of stress- and drug cue-related situations while blood oxygenation level-dependent signals of their brain were acquired in a 1.5T scanner. Spatial pre-processing and statistical analysis of brain images were performed. Regional brain activation was compared between stress and drug cue trials in men versus women. RESULTS: The results of our study showed greater activation in the left uncus and right claustrum (both, statistical threshold of P = 0.01, uncorrected; extent = 10 voxels) in men (n = 5) during drug cue trials compared with stress trials. No brain regions showed greater activation during stress trials compared with drug cue trials. In contrast, women (n = 6) showed greater activation in the right medial and superior frontal gyri during stress trials compared with drug cue trials at the same statistical threshold. No brain regions showed more activation during drug cue trials than during stress trials. CONCLUSIONS: The studies reviewed underscore the need to consider sex-related factors in examining the neuropathology of cocaine addiction. Our preliminary results also suggest important sex differences in the effect of stress- and drug cue-associated brain activation in individuals with cocaine use disorder.

Adult↗
PubMed1997

Sex differences in androgen-regulated expression of cytochrome P450 aromatase in the rat brain.

The basis of functional gender differences in adult responsiveness to testosterone (T) is not yet understood. Conversion of T to estradiol by cytochrome P450 aromatase in the medial preoptic area is required for the full expression of male sexual behavior in rats. High levels of aromatase are found in the medial preoptic nucleus (MPN) and in an interconnected group of sexually dimorphic nuclei which mediate masculine sexual behavior. Within this neural circuit, aromatase is regulated by T, acting through an androgen receptor (AR)-mediated mechanism. This arrangement constitutes a feedforward system because T is both the regulator and the major substrate of aromatase. Preoptic aromatase is thus more active in adult males than in females because of normal sex differences in circulating androgen levels. However, the mechanism of enzyme induction also appears to be sexually dimorphic because equivalent physiological doses of T stimulate aromatase to a greater extent in males than in females. Dose-response studies indicate that the sex difference is apparent over a range of circulating T concentrations and constitute a gender difference in T efficacy, but not potency. Sex differences in aromatase correlate with sex differences in nuclear AR concentrations in most regions of the sexually dimorphic neural circuit, but not in MPN. These results suggest that males may have larger populations of target cells in which aromatase is regulated by androgen, but the lack of a gender difference in AR levels in the MPN suggests that differences in post-receptor mechanisms could also be involved. Measurements of aromatase mRNA in androgen-treated gonadectomized rats demonstrate that sex difference in regulation is exerted pretranslationally. Taken together these results demonstrate a sexually dimorphic mechanism that could potentially limit the action of T in females, and may relate to the enhanced expression of T-stimulated sexual behaviors in males.

Androgens↗
PubMed2006

Sex differences in cerebral laterality of language and visuospatial processing.

Sex differences on language and visuospatial tasks are of great interest, with differences in hemispheric laterality hypothesized to exist between males and females. Some functional imaging studies examining sex differences have shown that males are more left lateralized on language tasks and females are more right lateralized on visuospatial tasks; however, findings are inconsistent. Here we used functional magnetic resonance imaging to study thirty participants, matched on task performance, during phonological and visuospatial tasks. For each task, region-of-interest analyses were used to test differences in cerebral laterality. Results indicate that lateralization differences exist, with males more left lateralized during the phonological task and showing greater bilateral activity during the visuospatial task, whereas females showed greater bilateral activity during the phonological task and were more right lateralized during the visuospatial task. Our data provide clear evidence for differences in laterality between males and females when processing language versus visuospatial information.

Adult↗
PubMed2002

Sex differences in opioid antinociception in rhesus monkeys: antagonism of fentanyl and U50,488 by quadazocine.

Sex differences have been observed in the antinociceptive effects of opioids in rodents and rhesus monkeys. Sex differences in the affinity of opioid ligands for opioid receptors may contribute to these findings. To test this hypothesis, the relative affinity of the competitive opioid antagonist quadazocine for mu and kappa opioid receptors was determined in rhesus monkeys using in vivo pA(2) analysis. The antinociceptive effects of the mu opioid agonist fentanyl and the kappa opioid agonist U50,488 were determined alone and after pretreatment with quadazocine in 4 females and 4 males using a warm-water tail-withdrawal assay of thermal nociception. The relative potency of quadazocine antagonism of fentanyl and U50,488 in females and males was used to assess sex differences in the relative affinity of quadazocine for mu and kappa receptors. Fentanyl was equipotent in female and male monkeys, and quadazocine was equipotent as an antagonist of fentanyl in females and males. In contrast, U50,488 was significantly less potent in females, and quadazocine was less potent as an antagonist of U50,488 in females. These findings suggest that opioid ligands have similar affinity for mu receptors but lower affinity for at least some kappa receptors in female than in male rhesus monkeys.

Journal Article↗
PubMed2003

Sex differences among five sources of motivation in the motivation sources inventory: preliminary findings.

Paper reports sex differences among five sources of motivation for a sample of 208 undergraduate students who completed the Motivation Sources Inventory. t tests yielded few statistically significant sex differences for the five sources of motivation; however, Instrumental Motivation was higher among men than women, while the remaining four motives showed no sex difference. Implications and research opportunities are discussed.

Adult↗
PubMed1986

Sex difference in maximal oxygen uptake. Effect of equating haemoglobin concentration.

Ten men and 11 women were studied to determine the effect of experimentally equating haemoglobin concentration ([Hb]) on the sex difference in maximal oxygen uptake (VO2max). VO2max was measured on a cycle ergometer using a continuous, load-incremented protocol. The men were studied under two conditions: 1) with normal [Hb] (153 g X L-1) and 2) two days following withdrawal of blood, which reduced their mean [Hb] to exactly equal the mean of the women (134 g X L-1). Prior to blood withdrawal, VO2max expressed in L X min-1 and relative to body weight and ride time on the cycle ergometer test were greater (p less than .01) in men by 1.11 L X min-1 (47%), 4.8 ml X kg-1 min-1 (11.5%) and 5.9 min (67%), respectively, whereas VO2max expressed relative to fat-free weight (FFW) was not significantly different. Equalizing [Hb] reduced (p less than .01) the mean VO2max of the men by 0.26 L X min-1 (7.5%), 3.2 ml X kg-1 min-1 (6.9%) or 4.1 ml X kg FFW-1 min-1 (7.7%), and ride time by 0.7 min (4.8%). Equalizing [Hb] reduced the sex difference for VO2max less than predicted from proportional changes in the oxygen content of the arterial blood and arteriovenous oxygen content difference during maximal exercise. It was concluded that the sex difference in [Hb] accounts for a significant, but relatively small portion of the sex difference in VO2max (L X min-1). Other factors such as the dimensions of the oxygen transport system and musculature are of greater importance.

Adult↗
PubMed1978

Sex differences on a measure of self-esteem: theoretical implications.

The hypotheses of this study of sex differences on a measure of self-esteem are as follows: 1) the scales good, nice, generous, pleasant, dependable, honest, and active will group together to form the outer esteem dimension of the semantic differential; 2) the scales strong, leader, powerful, confident, curious, inventive, sharp, and active will group together to form the inner esteem dimension of the semantic differential; 3) males will score significantly higher than females on the inner esteem dimension of the semantic differential; 4) females will score significantly higher than males on the outer esteem dimension of the semantic differential; 5) there will be a significnat difference between the scoring patterns of males and females on the two dimensions of the semantic differential after controlling for the effects of race and social desirability. The sample of 442 sixth through eighth grade students consisted of two subsamples made heterogeneous on race, geographic location, and type of school. The Frnks-Marolla Self-Esteem Semantic Differential and the Lunneborg and Lunneborg Child's Social Desirability Scale were administered. The findings support each of the hypotheses and indicate that there is a significant difference between the sexes on the Franks-Marolla Semantic Differential Measure of Self-Esteem. It is concluded that additional research in self-esteem might specify the meaning of sex differences in esteem by measuring esteem relative to an individual's structural social positions rather than measuring esteem in the general and environmentally nonspecific contexts as advocated by some.

Adolescent↗
PubMed1992

Sex steroids do not alter sex differences in tyrosine hydroxylase activity of dopaminergic neurons in vitro.

In order to distinguish the effects of genetic sex from those of sex hormones on the sexual differentiation of dopaminergic neurons, catecholamine synthesis was studied in gender-specific cultures of embryonic day-14 rat diencephalon. In addition to embryos from normal dams, embryos were used whose mothers had been treated with the estrogen antagonist tamoxifen or the testosterone antagonist cyproterone acetate on days 12 and 13 of gestation. Cultures from embryos of untreated dams were fed daily with a medium containing 17 beta-estradiol or testosterone. After 10 days in vitro, cultures were immunostained for tyrosine hydroxylase and the accumulation of dihydroxyphenylalanine (DOPA) was measured in the presence of the DOPA decarboxylase inhibitor NSD 1015. Rates of DOPA synthesis, unlike the numbers of tyrosine hydroxylase-immunoreactive neurons, were markedly higher in female cultures under all experimental conditions. Treatment of dams with antisteroids prior to removal of the embryos had no influence on these results. Treatment of cultures with both steroids decreased DOPA formation in a dose-dependent manner without altering the sex difference. These results suggest that cultured diencephalic dopaminergic neurons develop sex differences in the activity of tyrosine hydroxylase. This sexual dimorphism is initiated independently on the activity of gonadal steroid hormones. Sex hormones exert an additional modulatory influence on the activity of the enzyme but do not abolish or reverse sex differences. Therefore, the concept of a purely epigenetic mode of sexual differentiation of the mammalian brain needs to be broadened to incorporate other mechanisms, such as the cell-autonomous fulfillment of a sex-specific genetic program.

Animals↗
PubMed1991

Sex differences in cardiovascular reactivity: effects of the gender relevance of the stressor.

Suggests that sex differences in cardiovascular reactivity (CVR) in past research are a function of differences in cognitive appraisal of stressors as masculine or feminine tasks. In the present study, we examined the role of the gender relevance of the stressor as a mediator of sex differences in CVR. The CVR of male and female college students (n = 95) to the cold pressor test (CPT) was compared under masculine and gender-neutral instructions during an anticipation phase, a stressor phase, and a recovery phase. Men were expected to show greater CVR than women to the masculine CPT but not to the gender-neutral CPT. Results supported this prediction for systolic blood pressure reactivity and heart rate reactivity but not for diastolic blood pressure reactivity. The potential influence of sex differences in appraisal of situations on CVR and coronary heart disease is discussed.

Adolescent↗