Anxiety, sex-linked behaviors, and digit ratios (2D:4D)

The relationship between digit ratio (2D:4D) and intelligence levels in specific learning disorders

BACKGROUND

Higher prenatal testosterone exposure regulates brain development and affects learning and intelligence directly. The digit ratio (2D:4D) is regarded as an indicator of prenatal testosterone exposure. This study aims to investigate the 2D:4D ratios and intelligence levels in individuals with specific learning disorders (SLD) and compare the ratios with healthy subjects.

METHODS

The study included a total of 117 patients diagnosed with SLD and 67 healthy controls. We measured the 2D:4D ratios and administered the Wechsler-Intelligence Scale for Children-Revised to assess intelligence quotient (IQ) scores in the SLD group. Sociodemographic data was obtained for both patients and healthy subjects and compared in both groups, as well as 2D:4D ratios.

RESULTS

Compared to healthy controls, both-hand 2D:4D ratios were found to be lower in the SLD group. In addition, male and female participants with SLD showed lower 2D:4D ratios in both hands than controls. The total scores on the WISC-R were found to decrease as the right-hand 2D:4D ratios and the age increased in the SLD group.

CONCLUSION

Our findings add to the literature examining the influence of prenatal testosterone exposure on learning and intelligence in the SLD sample. Further research in this domain may yield valuable insights into the underlying mechanisms and potential clinical implications for the management of SLDs examining additional variables that could potentially impact alongside the impact of sex hormones on brain development.

Comparing Serum AMH, InhB, Testosterone Levels and Finger Length Ratio (2D/4D) of Male Children with Specific Learning Disorder and Controls

Introduction

It has been suggested that inhibin B (InhB), Anti-Müllerian hormone (Müllerian-inhibiting substance, AMH) levels, and 2D/4D finger length ratios are related to sex differences in neurodevelopmental disorders. The aim of this study is to investigate the role of InhB, AMH levels, and 2D/4D finger length ratios in male children with specific learning disorder (SLD).

Methods

The study included 38 male children diagnosed with SLD and 38 males of similar ages without SLD as the control group. Tests used in the evaluation were the Kiddie Schedule for Affective Disorders and Schizophrenia for School-Age Children-Present and Lifetime version, Specific learning disorder clinical observation battery, Wechsler Intelligence Scale for Children-Revised (WISC-R), and Conners' Parent Rating Scale.

Revised

Short Form. Serum AMH, InhB, and Testosterone levels were measured using an enzyme-linked immunosorbent assay.

Results

Male children diagnosed with SLD demonstrated significantly higher levels of serum InhB compared to controls (t= 2.59 p=0.009); both groups had similar levels of serum testosterone and AMH. The 2D/4D finger ratios in the SLD group were found to be lower than those in the control group (t= 2.92 p= 0.005). Serum InhB levels were positively correlated with WISC-R verbal scores (p= 0.003).

Conclusion

Our findings suggest that serum InhB levels and the 2D/4D ratio, which is an indicator of prenatal testosterone exposure, may play a role in the male predominance of SLD.

Androgen regulation of behavioral stress responses and the hypothalamic-pituitary-adrenal axis

Testosterone is a powerful steroid hormone that can impact the brain and behavior in various ways, including regulating behavioral and neuroendocrine (hypothalamic-pituitary-adrenal (HPA) axis) stress responses. Early in life androgens can act to alter development of brain regions associated with stress regulation, which ultimately impacts the display of stress responses later in life. Adult circulating androgens can also influence the expression of distinct genes and proteins that regulate stress responses. These changes in the brain are hypothesized to underlie the potent effects of androgens in regulating behaviors related to stress and stress-induced activation of the HPA axis. Androgens can induce alterations in these functions through direct binding to the androgen receptor (AR) or following conversion to estrogens and subsequent binding to estrogen receptors including estrogen receptor alpha (ERα), beta (ERβ), and G protein-coupled estrogen receptor 1 (GPER1). In this review, we focus on the role of androgens in regulating behavioral and neuroendocrine stress responses at different stages of the lifespan and the sex hormone receptors involved in regulating these effects. We also review the specific brain regions and cell phenotypes upon which androgens are proposed to act to regulate stress responses with an emphasis on hypothalamic and extended amygdala subregions. This knowledge of androgen effects on these neural systems is critical for understanding how sex hormones regulate stress responses.

Second to fourth digit ratio (2D:4D) as the 'anatomical marker' and reproductive 'hormonal fingerprint' in the occurrence dental plaque accumulation

OBJECTIVES

Digit ratio (2D:4D), as endocrine fingerprint, can indicate prenatal androgen exposure. It serves as an anatomical marker for various systemic diseases and a few studies relating it to oral health. The present study aims to evaluate the association between digit ratio and susceptibility to dental plaque formation.

METHODS

The study was conducted on young adults aged between 18 and 25 years. Digit ratio and reproductive hormones were measured; dental plaque score and gingival index (GI) were recorded. Data were analysed using the MedCalc. v.20.

RESULTS

Male and female participants were categorized into two groups based on their digit ratios being either above or below the calculated average (0.99 for females, 0.98 for males). Those with a digit ratio below the average had a significantly higher mean dental plaque score (p < 0.0001) than those with ratios at or above the average. However, there was no significant difference in the GI between the two groups. Reproductive hormone profiles varied significantly between the higher and lower digit ratio groups for both sexes.

CONCLUSIONS

Digit ratio may find potential to be used as an anatomical marker to identify the susceptibility to dental plaque build-up.

The Role of Sertoli Cell Hormones in Male Preponderance Observed in Autism Spectrum Disorder

Introduction

There is a significant, but poorly understood, male preponderance in prevalence of autism spectrum disorder (ASD). The aim of this study was to examine the relationship between male preponderance in ASD and Inhibin B (InhB) and Anti-Müllerian hormone (AMH) levels and the 2D/4D finger ratio associated with fetal androgen exposure.

Methods

42 patients with ASD and 42 neurotypical controls between the ages of 5 and 10 were included. ASD diagnosis and severity were determined using K-SADS PL (Kiddie-SADS - Present and Life Time) Version 2016 and the Childhood Autism Rating Scale (CARS). Serum InhB and AMH were measured. The 2D/4D finger length ratio was also calculated for hand anthropometric measurements.

Results

Serum InhB levels were higher in children diagnosed with ASD compared to the neurotypical controls (p=0.003). Serum AMH levels were similar in both groups. Positive correlation was determined between AMH and CARS scores (r=0.315, p=0.05). 2D/4D finger ratios in the ASD group were significantly lower than in the control group (p<0.001).

Conclusion

The study findings suggest that InhB, AMH, and fetal testosterone may be associated with male preponderance in ASD. More research is now required for a better understanding of this subject.

Finger-Length Ratios and Sexual Orientation in Southern Spain: A Large Sample Study on Sex-Linked Personality and Cognitive Traits

Some similarities between sex differences and sexual orientation differences, with gay men shifted in female-typical directions and lesbians shifted in male-typical directions, have been hypothesized to reflect the effects of prenatal androgen exposure. This report assessed sex-linked personality and cognitive traits in a Spanish sample of 1117 straight (i.e., heterosexual) and non-straight (i.e., non-heterosexual) men and women, using finger-length ratio (2D:4D) as an index of prenatal androgen exposure. Observed sex differences were in the expected direction: Measures of right-hand 2D:4D, left-hand 2D:4D, and anxiety were higher in straight women than men, whereas impulsivity, dominance, cognitive reflection, and mathematical proficiency were higher in straight men than women. Gay men proved to be shifted in a female-typical direction compared to straight men for right-hand 2D:4D, left-hand 2D:4D, anxiety, and cognitive reflection; they were intermediate for dominance and mathematics, and were shifted in a male-typical direction for impulsivity. Lesbians were shifted in a male-typical direction compared to straight women for left-hand 2D:4D, anxiety, cognitive reflection, and mathematics; and they were shifted in a highly female-typical direction for impulsivity and dominance (scoring lower than straight women). Observed sex-linked shifts in gay men and lesbians were larger for psychological traits that displayed larger sex differences, and smallest for impulsivity (which displayed the smallest sex difference). Evidence also suggested that sex-related measures were linked to 2D:4D in theoretically meaningful ways. In conclusion, this report suggests a plausible role of androgens as prenatal determinants of sex-linked personality and cognitive traits in straight and non-straight men and women.

Self-Efficacy and the Digit Ratio in a Group of Sports University Students

Self-efficacy is one's awareness of being able to cope optimally with different situations. Perceived self-efficacy is a belief that closely involves emotional and personological functioning. In fact, when one perceives oneself as capable, the likelihood of success increases significantly. The aim of this research was to verify a possible correlation between self-efficacy and the Digit Ratio (2D:4D), referred to as prenatal androgen levels, and whether these correlate with some psychological variables, considering possible gender differences. This study involved 56 sports university students, whose 2D:4D ratio was calculated. Moreover, self-assessment questionnaires: the Self-efficacy Scale (SES), the Big Five Questionnaire-2 (BFQ-2), the Profile of Mood State (POMS), the State-Trait Anxiety Inventory Form Y (STAI-Y) and the Emotional Regulation Questionnaire (ERQ) were administered. The data show that the perceived levels of self-efficacy seem to be influenced by an innate predisposition linked to prenatal androgen values to which the subjects were exposed during uterine life (2D:4D). This negative correlation indicates that the higher the value of the digit ratio, the more likely it is that the level of perceived self-efficacy will be lower. Finally, the degree of perceived self-efficacy also seems to depend on the levels of subjective anxiety, understood both as a personological disposition and a contingent condition, and the latter also seems to be influenced by prenatal androgen levels, particularly in women.

Cognitive Performances: The Role of Digit Ratio (D2:D4) With a Protective Factor for Anxiety

This study aimed to identify a possible correlation between the D2:D4 ratio and state and/or trait anxiety in adult healthy subjects and, if so, whether it exists any difference between men and women. In addition, we also wanted to observe whether there is a relationship between participants' age and state and/or trait anxiety. The research involved 125 subjects of both sexes, who were calculated the D2:D4 ratio and were administered the self-assessment questionnaire State-Trait Anxiety Inventory (STAI-Y). Results show that there are positive significant correlations between the D2:D4 ratio and score at state anxiety and trait anxiety, in the total sample. However, if men are examined separately from women, it can be observed that only men have a statistically significant relationship between D2:D4 ratios and state anxiety and trait anxiety. Moreover, about possible relations between the age of participants and state and trait anxiety, a significant negative relationship was observed, without differences between men and women. However, only subjects with a D2:D4 ratio ≥ 1, without differences between men and women, showed a statistically significant negative linear correlation between their age and their state and trait anxiety. The present data allow us to conclude that a low D2:D4 ratio (<1) represents a protective factor against anxiety in both men and women and that this protection seems likely to act throughout life.

Perceived fear of COVID-19 infection according to sex, age and occupational risk using the Brazilian version of the Fear of COVID-19 Scale

We investigated the fear of COVID-19 infection after proper translation and cultural adaptation of the "Fear of COVID-19 Scale" to the Brazilian Portuguese language. A sample of 1,743 Brazilian participants were included. The scale showed excellent psychometric characteristics. Women showed higher anxiety levels. Fear of COVID-19 scores were lower in males with occupational risk of contamination. On the other hand, women and younger individuals showed higher fear of COVID-19 infection scores. The Brazilian Fear of COVID-19 Scale proved to be a reliable tool with excellent psychometric properties for identifying fear of COVID-19 infection in the Brazilian population.

Molecular actions of sex hormones in the brain and their potential treatment use in anxiety disorders

Anxiety disorders are one of the most prevalent mood disorders that can lead to impaired quality of life. Current treatment of anxiety disorders has various adverse effects, safety concerns, or restricted efficacy; therefore, novel therapeutic targets need to be studied. Sex steroid hormones (SSHs) play a crucial role in the formation of brain structures, including regions of the limbic system and prefrontal cortex during perinatal development. In the brain, SSHs have activational and organizational effects mediated by either intracellular or transmembrane G-protein coupled receptors. During perinatal developmental periods, the physiological concentrations of SSHs lead to the normal development of the brain; however, the early hormonal dysregulation could result in various anxiety diorders later in life. Sex differences in the prevalence of anxiety disorders suggest that SSHs might be implicated in their development. In this review, we discuss preclinical and clinical studies regarding the role of dysregulated SSHs signaling during early brain development that modifies the risk for anxiety disorders in a sex-specific manner in adulthood. Moreover, our aim is to summarize potential molecular mechanisms by which the SSHs may affect anxiety disorders in preclinical research. Finally, the potential effects of SSHs in the treatment of anxiety disorders are discussed.

Understanding the Associations of Prenatal Androgen Exposure on Sleep Physiology, Circadian Proteins, Anthropometric Parameters, Hormonal Factors, Quality of Life, and Sex Among Healthy Young Adults: Protocol for an International, Multicenter Study

Background

The ratio of the second finger length to the fourth finger length (2D:4D ratio) is considered to be negatively correlated with prenatal androgen exposure (PAE) and positively correlated with prenatal estrogen. Coincidentally, various brain regions are sensitive to PAE, and their functions in adults may be influenced by the prenatal actions of sex hormones.

Objective

This study aims to assess the relationship between PAE (indicated by the 2D:4D ratio) and various physiological (sex hormone levels and sleep-wake parameters), psychological (mental health), and sexual parameters in healthy young adults.

Methods

This study consists of two phases. In phase 1, we will conduct a survey-based study and anthropometric assessments (including 2D:4D ratio and BMI) in healthy young adults. Using validated questionnaires, we will collect self-reported data on sleep quality, sexual function, sleep chronotype, anxiety, and depressive symptoms. In phase 2, a subsample of phase 1 will undergo polysomnography and physiological and genetic assessments. Sleep architecture data will be obtained using portable polysomnography. The levels of testosterone, estradiol, progesterone, luteinizing hormone, follicle-stimulating hormone, prolactin, melatonin, and circadian regulatory proteins (circadian locomotor output cycles kaput [CLOCK], timeless [TIM], and period [PER]) and the expression levels of some miRNAs will be measured using blood samples. The rest and activity cycle will be monitored using actigraphy for a 7-day period.

Results

In Poland, 720 participants were recruited for phase 1. Among these, 140 completed anthropometric measurements. In addition, 25 participants joined and completed phase 2 data collection. Recruitment from other sites will follow.

Conclusions

Findings from our study may help to better understand the plausible role of PAE in sleep physiology, mental health, and sexual quality of life in young adults.

International Registered Report Identifier (IRRID)

DERR1-10.2196/29199

Emotional stability is related to 2D:4D and social desirability in women: Possible implications on subjective well-being and psychopathology

Emotional stability-Neuroticism is a complex construct influenced by genetics and environmental factors. Women tend to exhibit higher neuroticism scores than men, which may be associated with an increased risk of suffering from some common mental conditions. Some authors have pointed out the influence of sex hormones, since they induce sexual differentiation of the brain that can lead to sex-specific behaviors. 2D:4D digit ratio is commonly used as a marker of prenatal sex hormones. In this study we analyzed whether there was an association between 2D:4D and personality measured through the BFQ in a homogeneous sample of 101 young women college students. We found a positive association between 2D:4D and emotional stability, as well as with its subdimensions emotion control and impulse control. This association could be quadratic and nonlinear. However, no association was found with the other four dimensions. We also measured anxiety, depression and global life satisfaction, variables related to neuroticism. We observed that emotional stability is positively associated to social desirability and global life satisfaction, and negatively related to anxiety and depression. On the other hand, we did not find any association between 2D:4D and anxiety, depression, and global life satisfaction. These results can be linked to other aspects such as subjective well-being and psychopathological symptoms. This study may help to better understand how these constructs are related and could lead to future projects to elucidated how these variables influence personality.

Investigation of second to fourth finger length ratio (2D:4D) in patients with bipolar disorder

Objective:

The etiology of bipolar disorder has yet to be fully elucidated, but differences in sex hormones have been suggested to play a role in its pathogenesis. An easily assessed marker of prenatal androgen exposure is the second-to-fourth-digit ratio (2D:4D) of the hand. In this study, we aimed to compare the 2D:4D ratio of patients with bipolar disorder to that of healthy controls.

Methods:

Seventy patients with bipolar disorder and 70 healthy controls, matched for age and sex, were included in the study. Finger lengths were measured from the palmar digital crease to the tip using a digital vernier caliper.

Results:

Patients with bipolar disorder had considerably higher right-hand 2D:4D ratios compared to controls. Both the right and left 2D:4D ratios of male patients were significantly greater than those of males in the control group. Female patients showed no differences in right or left 2D:4D ratio compared to healthy controls.

Conclusion:

These findings suggest that a high 2D:4D digit ratio of right hand is associated with the presence of bipolar disorder in males. Further large-scale, prospective studies are needed to explain the validity of this marker and its relationship with bipolar disorder.

Sexual Dimorphism in Titi Monkeys' Digit (2D:4D) Ratio is Associated with Maternal Urinary Sex Hormones During Pregnancy

The second-to-fourth digit (2D:4D) ratio is a sexually-dimorphic biomarker for prenatal sex hormone exposure. We investigated whether titi monkeys (Plecturocebus cupreus) exhibit sexually-dimorphic 2D:4D ratio, and whether variation in 2D:4D ratio correlates with maternal testosterone and estrogen levels during early pregnancy. Subjects were 61 adult titi monkeys (32 males, 29 females). For 26 subjects, maternal urine samples were collected approximately 15-20 weeks before birth and assayed for testosterone and estrone conjugate (E1 C). Titi monkeys exhibited a human-like pattern of sexual dimorphism in right-hand 2D:4D ratio, with females exhibiting higher 2D:4D ratio than males (β = -0.29, p = 0.023). For left-hand 2D:4D ratio, high levels of maternal E1 C predicted low offspring 2D:4D ratio (β = -0.48, p = 0.009). For right-hand 2D:4D ratio, high levels of testosterone (β = -0.53, p = 0.005) and testosterone-to-E1 C ratio (β = -0.41, p = 0.028) predicted low offspring 2D:4D ratio. For 2D:4D ratio asymmetry (right-hand - left-hand), high levels of testosterone (β = -0.43, p = 0.03) and testosterone-to-E1 C ratio (β = -0.53, p = 0.003) predicted low (right-biased) asymmetry. This is the first report of sexually-dimorphic 2D:4D ratio in New World monkeys, and the results support a growing literature suggesting prenatal sex hormones may modulate offspring 2D:4D ratio.

Masculinized Second-to-Fourth Digit Ratio (2D:4D Ratio) Is Associated With Lower Cortisol Response in Infant Female Rhesus Monkeys (Macaca mulatta)

The second-to-fourth digit ratio (2D:4D ratio) is considered a postnatal proxy measure for the degree of prenatal androgen exposure (PAE), which is the primary factor responsible for masculinizing the brain of a developing fetus. Some studies suggest that the organizational effects of PAE may extend to the hypothalamic-pituitary-adrenal (HPA) axis response to stress. This study investigates the relationship between 2D:4D ratio and HPA axis functioning using a rhesus monkey (Macaca mulatta) model. Subjects were N = 268 (180 females, 88 males) rhesus monkey infants (3–4 months of age). Plasma cortisol concentrations were assayed from two blood samples obtained during a 25-h experimental social separation stressor at 2- and 7-h post-separation. Subjects’ 2D:4D ratio was measured later in life (M_age = 6.70 years). It was hypothesized that infant rhesus monkeys that exhibited a more masculine-like 2D:4D ratio would show lower levels of circulating cortisol after a social separation and relocation stressor. The results showed that there was a sex difference in the left-hand 2D:4D ratio. The results also showed that there was an overall sex difference in cortisol concentrations and that female, but not male, monkeys that exhibited a more masculine-like right- and left-hand 2D:4D ratio exhibited lower mean stress-induced cortisol concentrations early in life. These findings suggest that higher levels of prenatal androgens in females, as measured by 2D:4D ratio, may be related to an attenuated HPA axis stress-response, as measured by plasma cortisol levels. To the extent that these findings generalize to humans, they suggest that the organizational effects of PAE extend to the infant HPA axis, modulating the HPA axis response, particularly in females.

Lower Digit Ratio (2D:4D) Indicative of Excess Prenatal Androgen Is Associated With Increased Sociability and Greater Social Capital

Positive social interactions are crucial for human well-being. Elevated prenatal exposure to testosterone as indicated by a low second-to-fourth finger length ratio (2D:4D) relates to more aggressive/hostile behavior in men of low 2D:4D, especially in challenging situations. How much people enjoy interacting with others is determined by the personality trait sociability. Given its role in approach and avoidance behavior, sociability might also be influenced by prenatal sex hormones, but studies are inconclusive so far. Here, we investigated the association between 2D:4D and the personality trait sociability complemented by personal social capital and personal social network size, in a population-based cohort of 4998 men. Lower 2D:4D correlated significantly with higher trait sociability, bigger personal social capital, and larger personal social network size. These effects were consistent across both hands separately and their mean value. Furthermore, both factors of sociability (1) liking party and company of friends and (2) isolation intolerance, correlated significantly with the prenatal testosterone marker. The exploratory analysis revealed no link between 2D:4D and responses to the personality trait aggression items or items of anti-social-personality disorder. Our data suggest that prenatal androgen exposure organizes the brain with lasting effects on social behavior.

Digit ratio (2D:4D) and its behavioral correlates in infant rhesus macaques (Macaca mulatta)

2D:4D ratios are typically lower in adult human males than females and are linked to numerous sex-differentiated behaviors. 2D:4D ratios are considered an indicator of prenatal androgen exposure; if so, children's 2D:4D ratios would arguably be even better indicators of prenatal androgen exposure since children have experienced fewer postnatal influences than adults. However, sex differences in 2D:4D ratios as well as associations between 2D:4D ratios and sex-typed behaviors in children have been inconsistent. Several studies also report sex differences and behavioral correlates of 2D:4D ratios in adult non-human primates, but little is known about 2D:4D ratios in infant non-human primates. This study examined sex differences in 2D:4D ratios over the first month of life, and associations with behavioral outcomes at 12-24 weeks of age, in N = 304 infant rhesus macaques. An increase in 2D:4D ratios over the first month of life was found, as well as associations with aggression and play behaviors, but no sex differences in 2D:4D ratios were observed. These results highlight the need for future developmental studies of 2D:4D ratios in order to determine not only their stability and predictive value, but also to discern the mechanism connecting prenatal androgen exposure, 2D:4D ratios, and behavioral outcomes.

2D:4D ratios as an indicator of intrauterine androgen exposure in children who stutter

AIM

We aimed to explore whether there is a relationship between stuttering and digit ratio (2D:4D), which is thought to be a marker of prenatal testosterone exposure.

METHODS

We evaluated a total of 90 children who stutter (CWS; n = 40 mild-to-moderate and n = 50 severe stutters) and 40 healthy peers (CWNS) as controls. We used the Clinical Global Impression-Severity (CGIS) scale to measure the severity of stuttering. We measured the lengths of index finger (2D) and ring finger (4D) of both hands directly and divided to calculate 2D:4D ratio. The difference between the right and the left hand 2D:4D ratio (D_R-L) was also calculated.

RESULT

Significant difference was found in right 2D:4D and the mean D_R-L between the CWS and CWNS groups. Right 2D:4D was significantly lower in stuttering boys than in control boys, and in stuttering girls than control girls. Also, D_R-L was significantly lower in stuttering boys than control boys. In ANOVA, there were significant differences between the mild-to-moderate, severe stuttering and control groups in terms of right 2D:4D and D_R-L. Right hand 2D:4D and D_R-L decreased from controls to severe stutterers.

CONCLUSION

Our results suggest that lower right 2D:4D and D_R-L were related to the presence and severity of stuttering in children, i.e. CWS had lower 2D:4D and D_R-L than CWNS. Further large-scale prospective studies are needed to clarify the reliability of 2D:4D ratio as an indicator of fetal sex hormone exposure level and its relation with the presence and severity of stuttering in children.

Gender Differences in Large-Scale and Small-Scale Spatial Ability: A Systematic Review Based on Behavioral and Neuroimaging Research

Background: As we human beings are living in a multidimensional space all the time. Therefore, spatial ability is vital for the survival and development of individuals. However, males and females show gender differences in this ability. So, are these gender differences influenced by the scale type of spatial ability? It's not well specified. Therefore, to tackle this issue, we conducted the current research from the behavioral and neural level. Methods: Study 1 used the general meta-analysis method to explore whether individuals display the same gender differences in large- and small-scale spatial ability. Study 2 used the method of Activation Likelihood Estimation to identify the commonalities and distinctions of the brain activity between males and females on large- and small-scale spatial ability. Results: Study 1 showed that in behavior performance, males outperformed females in both large-scale and small-scale spatial ability, but the effect size of the gender difference in large-scale spatial ability is significantly greater than that in small-scale spatial ability. In addition, Study 2 showed that in terms of neural activity, males and females exhibited both similarities and differences no matter in large-scale or small-scale spatial ability. Especially, the contrast analysis between females and males demonstrated a stronger activation in the brain regions of bilateral lentiform nucleus and bilateral parahippocampal gyrus in large-scale spatial ability, and correspondence in right sub-gyral, right precuneus, and left middle frontal gyrus in small-scale spatial ability. Conclusions: The results indicated that the reason why females performed not so well in large-scale spatial ability was that they were more susceptible to emotions and their parahippocampal gyrus worked less efficiently than males; females performed not so well in small-scale spatial ability because they mostly adopted the egocentric strategy and their sub-gyral also worked less efficiently than males. The two different reasons have made for gender differences in favor of males in terms of spatial ability and such gender differences have different manifestations in large-scale and small-scale spatial ability. Possible implications of the results for understanding the issue of gender differences in spatial ability are discussed.

Depressed female cynomolgus monkeys (Macaca fascicularis) display a higher second-to-fourth (2D:4D) digit ratio

This research aimed to provide evidence of a relationship between digit ratio and depression status in the cynomolgus monkey (Macaca fascicularis). In stable cynomolgus monkey social groups, we selected 15 depressed monkeys based on depressive-like behavioral criteria and 16 normal control monkeys. All animals were video recorded for two weeks, with the duration and frequency of the core depressive behaviors and 58 other behaviors in 12 behavioral categories then evaluated via behavioral analysis. Finger lengths from the right and left forelimb hands of both groups were measured by X-ray imaging. Finger length and digit ratio comparisons between the two groups were conducted using Student’s t-test. In terms of the duration of each behavior, significant differences emerged in “Huddling” and five other behavioral categories, including Ingestive, Amicable, Parental, Locomotive, and Resting. In addition to the above five behavioral categories, we found that depressed monkeys spent less time in parental and rubbing back and forth behaviors than the control group. Furthermore, the 4th fingers were significantly longer in the left and right hands in the control group relative to the depressed monkeys. The second-to-fourth (2D:4D) digit ratio in the left and right forelimb hands was significantly lower in the control group than that in the depressed group. Our findings revealed significant differences in finger lengths and digit ratios between depressed monkeys and healthy controls, which concords with our view that relatively high fetal testosterone exposure may be a protective factor against developing depressive symptoms (or that low fetal testosterone exposure is a risk factor).

Sex Differences in Rhesus Monkeys' Digit Ratio (2D:4D Ratio) and Its Association With Maternal Social Dominance Rank

Prenatal androgen exposure (PAE) plays a pivotal role in masculinizing the developing body and brain, and extreme exposure may contribute to autism, anxiety disorder and schizophrenia. One commonly used biomarker for PAE is the pointer-to-ring-finger digit length (2D:4D) ratio. Although this biomarker is widely used in human studies, relatively few studies have investigated 2D:4D ratio in nonhuman primates, particularly rhesus macaques (Macaca mulatta), one of the most commonly used animals in biomedical research. Thus far, data suggest that sexual dimorphism in 2D:4D ratio may be in the opposite direction in some monkey species, when compared to the pattern exhibited by humans and great apes. Using a large sample size, we investigated whether rhesus monkeys' 2D:4D ratio shows the same sex-differentiated pattern present in other Old World monkey species. We also investigated whether individual differences in 2D:4D ratio are associated with the social dominance rank of subjects' mothers during pregnancy, and the social dominance rank the subjects attained as adults. Subjects were 335 rhesus monkeys between 3 years and 24 years of age (M = 6.6). Maternal dominance rank during pregnancy and subjects' adult dominance rank were categorized into tertiles (high, middle and low). Results showed that, across both hands, male rhesus monkeys exhibited higher 2D:4D ratio than females, a pattern consistent with other monkey species and a reversal from the pattern typically observed in humans and apes. This sex difference was modulated by maternal dominance rank, with female offspring of high-ranking and middle-ranking mothers exhibiting masculinized 2D:4D ratio, indicating that maternal dominance rank during pregnancy may influence levels of PAE. There was no association between subjects' 2D:4D ratio and the social dominance rank they attained as adults. These findings show a consistent sex difference in Old World monkeys' 2D:4D ratio that diverges from the pattern observed in apes and humans, and suggest maternal social dominance rank modulates PAE in rhesus monkeys.

Second-to-fourth digit length ratio is associated with negative and affective symptoms in schizophrenia patients

BACKGROUND

Higher levels of circulating oestrogens in women and testosterone in men have been shown to have a protective effect against the clinical manifestations of schizophrenia, mostly with respect to negative symptomatology. Certain studies suggest that they also have a protective effect against the neuropsychological impairment observed in the disease. We investigated whether greater prenatal exposure to estrogens in women and to testosterone in men, reflected by the 2D:4D ratio, was similarly associated with decreased negative symptomatology and improved neuropsychological functioning in patients.

METHOD

51 schizophrenia patients and 50 healthy participants were administered a neuropsychological battery. The 2D:4D ratio was measured in all participants. Positive, negative, and affective symptoms were assessed in patients. Regression analyses were conducted separately in male and female subgroups.

RESULTS

No associations with positive symptoms were revealed. In male patients, the 2D:4D ratio was positively associated with avolition and inversely associated with anxiety. In female patients, it was inversely associated with alogia, and tended to be positively associated with depression. No association between higher prenatal concentration of the relevant sex hormone and improved neuropsychological performance emerged in patients.

CONCLUSIONS

Higher concentrations of prenatal testosterone in male patients, and prenatal oestrogens in female patients, are associated with a decrement in certain aspects of negative symptomatology. In addition, prenatal sex hormone concentration seems to be associated with predisposition to anxiety in male patients, and to depression in female patients.

Antenatal ultrasound value in risk calculation for Autism Spectrum Disorder: A systematic review to support future research

There is a growing research interest on the antenatal features of children with neurodevelopmental disorders. Indeed, it has been proved that the neurodevelopment is, at least partly, affected by processes occurring in fetal life and that the early neurodevelopmental disorders identification is essential to optimize long-term outcomes. This systematic review aims to summarize findings on antenatal ultrasound data, which are or might be considered early risk indexes of postnatal social impairments. We conducted systematic searches in Pubmed and PsychINFO databases to identify studies including fetal ultrasound measurements and postnatal neurodevelopmental outcome assessment. The bibliographic search included 3203 articles but after the assessment of the eligibility conducted by two independent researchers, only 26 studies were selected. Some alterations in ultrasound antenatal measurements (such as biophysical data, nuchal thickness and enlargement of cerebral ventricles) have been associated to autism spectrum disorder. However, data are still limited, controversial and not specific. Reported data are here discussed to strongly support studies on fetuses at high risk for autism spectrum disorder.

Age of pubertal onset and 2nd to 4th digit ratios: Preliminary findings

BACKGROUND

The second to fourth digit ratio (2D:4D) is used as a marker of prenatal sex hormone exposure. The aim of this study was to evaluate the possible relation between digit ratio and age of pubertal onset.

METHODS

Participants were 321 men and 202 women aged between 18 and 28 at the time of assessment who self-reported their onset of puberty (i.e., age at first conscious ejaculation or menarche). Participants' right and left digit lengths were measured from hand scans.

RESULTS

All groups of males, i.e., early, average, and late pubertal onset, had lower mean 2D:4D than the comparable female groups, regardless of the relative timing of their pubertal onset. Among the males, there was a significant difference in digit ratios between individuals who experienced early, average, and late onset of puberty. In the males, we observed a positive relationship between 2D:4D and age of pubertal onset for both right and left hands. There were no significant differences in 2D:4D among the three groups of female maturers. We observed no significant association between digit ratios and age at menarche.

CONCLUSIONS

These data lend further support for using 2D:4D as a measure of prenatal androgen exposure.

Sex differences in visual-spatial working memory: A meta-analysis

Visual-spatial working memory measures are widely used in clinical and experimental settings. Furthermore, it has been argued that the male advantage in spatial abilities can be explained by a sex difference in visual-spatial working memory. Therefore, sex differences in visual-spatial working memory have important implication for research, theory, and practice, but they have yet to be quantified. The present meta-analysis quantified the magnitude of sex differences in visual-spatial working memory and examined variables that might moderate them. The analysis used a set of 180 effect sizes from healthy males and females drawn from 98 samples ranging in mean age from 3 to 86 years. Multilevel meta-analysis was used on the overall data set to account for non-independent effect sizes. The data also were analyzed in separate task subgroups by means of multilevel and mixed-effects models. Results showed a small but significant male advantage (mean d = 0.155, 95 % confidence interval = 0.087-0.223). All the tasks produced a male advantage, except for memory for location, where a female advantage emerged. Age of the participants was a significant moderator, indicating that sex differences in visual-spatial working memory appeared first in the 13-17 years age group. Removing memory for location tasks from the sample affected the pattern of significant moderators. The present results indicate a male advantage in visual-spatial working memory, although age and specific task modulate the magnitude and direction of the effects. Implications for clinical applications, cognitive model building, and experimental research are discussed.

2D:4D Ratio and its Implications in Medicine

Digit ratios, especially 2D:4D ratio, a potential proxy marker for prenatal androgen exposure shows sexual dimorphism. Existing literature and recent research show accumulating evidence on 2D:4D ratio showing correlations with various phenotypic traits in humans. Ratio of 2D:4D is found to correlate negatively to testosterone and positively to oestrogen in the foetus. Interestingly, it is constant since birth and not influenced by the adult hormone levels. Usually, males have lower ratios when compared to females. Prenatal androgen exposure and therefore, digit ratios have been reported to be associated with numerical competencies, spatial skills, handedness, cognitive abilities, academic performance, sperm counts, personalities and prevalence of obesity, migraine, eating disorders, depression, myopia, autism etc. The authors have attempted to write a brief account on the digit ratios and the dimorphism observed in various physiological, psychological and behavioural traits. Also, the authors have discussed the relevant molecular basics and the methods of measurement of digit ratios.

Umbilical cord blood testosterone and childhood internalizing and externalizing behavior: a prospective study

Antenatal testosterone exposure influences fetal neurodevelopment and gender-role behavior in postnatal life and may contribute to differences in developmental psychopathology during childhood. We prospectively measured the associations between umbilical cord blood testosterone levels at birth and childhood behavioral development in both males and females from a large population based sample. The study comprised 430 females and 429 males from the Western Australian Pregnancy Cohort (Raine) Study where umbilical cord blood had been collected. Total testosterone concentrations were determined by mass spectrometry and bioavailable testosterone (BioT) levels were calculated. At two, five, eight and ten years of age, the participants completed the Child Behavior Checklist (CBCL). Linear regression models were used to analyse the relationship between BioT concentrations (in quartiles) and CBCL scores (total, internalizing, externalizing and selected syndrome). Boys had higher mean CBCL T-scores than girls across all ages of follow-up. There was no significant relationship between cord blood BioT quartiles and CBCL total, internalizing and externalizing T-scores at age two or five to ten combined. In the syndrome score analyses, higher BioT quartiles were associated with significantly lower scores for attention problems for boys at age five, eight and ten, and greater withdrawal symptoms in pre-school girls (age five). We did not identify a consistent relationship between antenatal testosterone exposure and total, internalizing or externalizing behavioral difficulties in childhood. Higher umbilical cord BioT levels were associated with lower scores for attention problems in boys up to 10 years and more withdrawn behavior in 5-year-old girls; however, these findings were not consistent across ages and require further investigation in a larger sample.

Meta-analysis of digit ratio 2D:4D shows greater sex difference in the right hand

OBJECTIVES

Our aims are, first, to describe the sex difference in the length ratio of the second and fourth digits (2D:4D), which likely reflects prenatal testosterone levels in humans. Second, to infer the loss of reliability observed in 2D:4D based on self-measured finger lengths.

METHODS

We used random-effects meta-analysis of 2D:4D based on expert-measured finger lengths (116 samples with 13,260 females and 11,789 males).

RESULTS

We find a moderate sex difference (with lower 2D:4D for males), which shows substantial heterogeneity (which is unrelated to age). The sex difference is moderated by the type of finger length measurement and by hand. Measurement involving the distortion of soft tissue leads to a significantly larger sex difference than finger length measurement avoiding this. The sex difference in 2D:4D is larger in the right hand than in the left. The reliability of self-measured 2D:4D in the BBC internet study, by far the largest study on 2D:4D, is estimated to be 46% of that of expert-measured 2D:4D.

CONCLUSIONS

Right-hand 2D:4D might be a better indicator of prenatal androgenisation than left-hand 2D:4D. The view that 2D:4D has allometric properties (Kratochvil L, Flegr J. 2009. Differences in 2nd to 4th digit length ratio in humans reflect shifts along the common allometric line. Biol Lett 5:643-646.) is not supported. Bone lengths contribute to the sex difference in 2D:4D. In addition, there might be a sex difference in fingers' soft tissue, which should be investigated. Because of measurement unreliability, correlations between 2D:4D and variables of interest are about one-third smaller in the BBC internet study than in studies in which 2D:4D is based on expert-measured finger lengths.

No association between the 2D:4D fetal testosterone marker and multidimensional attentional abilities in children with ADHD

AIM

It has been suggested that high levels of prenatal testosterone exposure are implied in the aetiology of attention-deficit-hyperactivity disorder (ADHD). This study examined the association between the ratio of the length of the second and fourth digits (2D:4D ratio), a marker of fetal testosterone exposure, and the presence of ADHD-related cognitive and behavioural problems in children with ADHD and in typically developing comparison individuals.

METHOD

A clinically referred group of 64 children who fulfilled DSM-IV-TR criteria for ADHD (47 males, 17 females; mean age 8 y 8 mo, SD 1 y 8 mo, range 7-12 y) and 46 comparison children (25 males, 21 females; mean age 9 y 2 mo; SD 1 y 10 mo, range 7-12 y) were included in the study. The length of the second and fourth digits was measured by two independent raters. The Child Behaviour Checklist (CBCL) and the Test of Everyday Attention for Children (TEA-Ch) were used to assess behavioural problems and different aspects of attention.

RESULTS

No group differences in 2D:4D ratio were observed between children with (combined, inattentive, or hyperactive-impulsive subtype of) ADHD and comparison children. The ratio did not show the postulated relation with cognitive and behavioural aspects of ADHD.

INTERPRETATION

These findings challenge the hypothesis that fetal testosterone exposure plays a prominent role in the aetiology of ADHD.

Scientometric analysis and bibliography of digit ratio (2D:4D) research, 1998-2008

A scientometric analysis of modern research on the second-to-fourth digit ratio (2D:4D), a widely studied putative marker for prenatal androgen action, is presented. In early 2009, this literature totalled more than 300 publications and, since its initiation in 1998, has grown at a rate slightly faster than linear. Key findings included evidence of publication bias and citation bias, incomplete coverage and outdatedness of existing reviews, and a dearth of meta-analyses in this field. 2D:4D research clusters noticeably in terms of researchers, institutions, countries, and journals involved. Although 2D:4D is an anthropometric trait, most of the research has been conducted at psychology departments, not anthropology departments. However, 2D:4D research has not been predominantly published in core and specialized journals of psychology, but rather in more broadly scoped journals of the behavioral sciences, biomedical social sciences, and neurosciences. Total citation numbers of 2D:4D papers for the most part were not larger than their citation counts within 2D:4D research, indicating that until now, only a few 2D:4D studies have attained broader interest outside this specific field. Comparative citation analyses show that 2D:4D research presently is commensurate in size and importance to evolutionary psychological jealousy research, but has grown faster than the latter field. In contrast, it is much smaller and has spread more slowly than research about the Implicit Association Test Fifteen conjectures about anticipated trends in 2D:4D research are outlined, appendixed by a first-time bibliography of the entirety of the published 2D:4D literature.