Hemispheric Differences in Corticospinal Excitability and in Transcallosal Inhibition in Relation to Degree of Handedness

In this study, we examined hemispheric differences in corticospinal excitability and in transcallosal inhibition in a selected group of young adults (n = 34) grouped into three handedness categories (RH: strongly right-handed, n = 17; LH: strongly left-handed, n = 10; MH: mixed-handed, n = 7) based on laterality quotients (LQ) derived from the Edinburgh Handedness Inventory. Performance measures were also used to derive a laterality index reflecting right-left asymmetries in manual dexterity (Dext_li) and in finger tapping speed (Speed_li). Corticospinal excitability was assessed in each hemisphere by means of transcranial magnetic stimulation (TMS) using the first dorsal interosseus as the target muscle. TMS measures consisted of resting motor threshold (rMT), motor evoked potential (MEP) recruitment curve (RC) and the contralateral silent period (cSP) with the accompanying MEP facilitation. Hemispheric interactions were assessed by means of the ipsilateral silent period (iSP) to determine the onset latency and the duration of transcallosal inhibition (i.e., LTI and DTI). Analysis of hemispheric variations in measures of corticospinal excitability revealed no major asymmetries in relation to degrees of laterality or handedness, with the exception of a rightward increase in rMTs in the LH group. Similarly, no clear asymmetries were found when looking at hemispheric variations in measures of transcallosal inhibition. However, a large group effect was detected for LTI measures, which were found to be significantly shorter in the MH group than in either the LH or RH group. MH participants also tended to show longer DTI than the other participants. Further inspection of overall variations in LTI and DTI measures as a function of LQs revealed that both variables followed a non-linear relationship, which was best described by a 2^nd order polynomial function. Overall, these findings provide converging evidence for a link between mixed-handedness and more efficient interhemispheric communication when compared to either right- or left-handedness.     

Three palmar dermatoglyphic traits and their asymmetry in Bulgarian right-, mixed- and left-handers

Summary: In a sample, comprising 264 right-, 246 mixed- and 360 left-handers (RH, MH and LH, correspondingly), the atd-angle, the a-b ridge count and the hypothenar radial arch were investigated, the asymmetry of both quantitative traits differentiated into directional (DA) and fluctuating (FA) one. Except for the FA of the a-b ridge count in females, which decreased significantly from RH to LH, the trends observed in the relations between the investigated dermatoglyphic values and handedness were not significant. In both quantitative traits the most important finding was the categorical left-palm excess over the right palm, since it was significantly related to sex and handedness, being much more expressed in females than in males and in the non-right-handers than in the right-handers. The hypothenar radial arch, along with its considerably higher frequency in females than in males and on the right palm than on the left, as well as its rarity combined with a very high symmetry, displayed another interesting peculiarity. The pattern was 3.9-fold more frequent in the MH and 3.4-fold more frequent in the LH as compared to RH. As witnessed by the odds ratio, if a given palm belongs to a non-right-hander, the probability that it bears a hypothenar radial arch is nearly 4-fold higher than if it were a palm of a right-hander. Arguments are adduced that left-handedness, although not a pathological character is, to say the least, a modified condition and that, similarly, the hypothenar radial arch is a subnormal dermatoglyphic finding. If such is the case, their relationship found by the present study is not surprising, although its causal background still remains unclear.     

Digital dermatoglyphics of Bulgarians from northeast Bulgaria

Digital dermatoglyphics were collected from 1,065 male and 1,065 female Bulgarians from northeast Bulgaria. None of the subjects had a diagnosed or suspected genetic or chronic disease of any kind. The fingerprints were classified by the 18-type system of Monique de Lestrange, modified to provide rapid and easy comparison with simpler classification systems. All the standard finger pattern indices were calculated. Certain modifications were introduced into the delta indices, it being borne in mind that each tented arch possesses a triradius and each complex (three-centered, accidental) whorl contains three triradii. A deltadiagram was constructed and its configuration was compared with those of some other populations. In addition, a new radioulnar index was proposed, representing a ratio between all the radial and all the ulnar patterns. The total, absolute, ulnar and radial finger ridge counts were calculated and their sample distributions were investigated. The dermatoglyphic features were evaluated and presented for each sex and each hand separately in order to investigate both the sex and bilateral differences. The set of data presented in this paper is a component of the physical anthropology of the general Bulgarian population. At the same time these data can be used as controls when analyzing the dermatoglyphic findings in Bulgarian patients with genetic diseases or congenital malformations.     

Hormones and handedness

BACKGROUND: The Wessex Growth Study has monitored the growth and psychological development of short normal (SN) and average height control subjects since they entered school in 1985/1986. During psychometric testing, we found that 25% SN compared to 9% control subjects wrote with their left hand. The short group also attained significantly lower scores on measures of IQ and attainment and displayed less internalisation of control. Laterality, however, is thought to be influenced by the intrauterine environment and has been associated with pubertal delay. At recruitment, short children had a relatively low birth weight, delayed bone age and were more likely than controls to be short for family. OBJECTIVES: To determine if birth conditions were associated with lateral preference and whether laterality could account for the differences found during the psychometric assessment or predict pubertal timing of SN children. METHODS: Subjects were classified as right- (RH) or left-handed (LH) according to the writing hand and the data were investigated examining the effect of handedness and stature. RESULTS: RH and LH SN children were no more likely to suffer birth complications than those of average height. Psychometric testing did not reveal any significant differences between RH and LH SN children and their patterns of growth appeared to be similar. However, both RH and LH SN children scored less well on tests of cognitive ability and analyses of covariance revealed significant gender/handedness effects for both the timing of puberty and final height. CONCLUSIONS: The increase in left-handedness among SN children did not appear to be related to adverse birth conditions, but it may be that the hormones responsible for growth and development also play some part in brain laterality and cognitive development.     

Sexual dimorphism in dermatoglyphic traits and fluctuating asymmetry in Bulgarians from northeast Bulgaria

In parallel with the development of dermatoglyphics as a method of identification, data have been accumulated on the characteristics of fingerprints related to sex and ethnic origin which make up the statistical basis of this study. The aims of the present study are to determine phenotype variations in the asymmetry of dermatoglyphics in both sexes within the scope of the entire hand skin ridge system; to investigate correlations between the phenotypes; and, to assess the fluctuating asymmetry among the Bulgarian population from the region of northwest Bulgaria. The sample consists of 894 unrelated, clinically healthy individuals (480 females and 414 males) aged 18–50 years, who live in towns and villages in the northwest provinces.Finger and palmar prints were collected using rolled print (inked) method. Twenty dermatoglyphics variables of fingers and hands, separately for right and left hands and jointly for both hands, were statistically assessed. The material was processed by SPSS 12 software. The results of the present study show distinctive sexual differences. Higher values in males are recorded in finger ridge counts, the Furuhata and Cummins indices, the palm ridge counts and the overall ridge counts in all interdigital areas. Males have higher frequency values in patterns Hy, Th/III and Th/IV.     

Human handedness and scalp hair-whorl direction develop from a common genetic mechanism

Theories concerning the cause of right- or left-hand preference in humans vary from purely learned behavior, to solely genetics, to a combination of the two mechanisms. The cause of handedness and its relation to the biologically specified scalp hair-whorl rotation is determined here. The general public, consisting of mostly right-handers (RH), shows counterclockwise whorl rotation infrequently in 8.4% of individuals. Interestingly, non-right-handers (NRH, i.e., left-handers and ambidextrous) display a random mixture of clockwise and counterclockwise swirling patterns. Confirming this finding, in another independent sample of individuals chosen because of their counterclockwise rotation, one-half of them are NRH. These findings of coupling in RH and uncoupling in NRH unequivocally establish that these traits develop from a common genetic mechanism. Another result concerning handedness of the progeny of discordant monozygotic twins suggests that lefties are one gene apart from righties. Together, these results suggest (1) that a single gene controls handedness, whorl orientation, and twin concordance and discordance and (2) that neuronal and visceral (internal organs) forms of bilateral asymmetry are coded by separate sets of genetic pathways. The sociological impact of the study is discussed.     

Quantitative finger dermatoglyphics in the Mediterranean region of Murcia,Spain

Quantitative finger dermatoglyphics have been analyzed in a Spanish population on the Mediterranean coast, from a sample of 347 individuals (163 males and 184 females) whose four grandparents were born in the studied region (Murcia). From the prints of the sampled individuals, radial, ulnar, and maximal ridge counts have been examined using classical methodology according to the pattern orientation. Kolmogorov test was used to evaluate the normality of the count values. Paired t-test, t-test for two samples, and Wilcoxon and Mann-Whitney non-parametric U test were used to explore bimanual and sexual differences. Maximal and radial ridge counts show similar distributions fitting into a normal distribution. Instead, ulnar values show a particular distribution clearly different from normality. The bilateral and sexual differentiation patterns reveal the divergence between the ulnar counts and the maximal and radial values. In comparison to other Iberian populations our results show a particular position of Murcia with the lowest TFRC values in the Spanish variation ranges.     

Population-level right-handedness for a coordinated bimanual task in naturalistic housed chimpanzees: replication and extension in 114 animals from Zambia and Spain

Recently, many studies have been conducted on manual laterality in chimpanzees. Nevertheless, whether nonhuman primates exhibit population-level handedness remains a topic of considerable debate. One of the behaviors studied has been bimanual coordinated actions. Although recent studies have highlighted that captive chimpanzees show handedness at population level for these tasks, some authors have questioned the validity and consistency of these results. The first reason has been the humanization of the samples. The second one has been that the results refer to animals in American biomedical centers and the studies were conducted by the same team [WD Hopkins et al.]. This article aims to assess the laterality in bimanual coordination (tube task) activities in animals housed in an intermediate environment (Chimfunshi, Zambia). This has been conducted by replicating previous studies on similar samples (Mona Foundation, Spain), and then by extending the results to chimpanzees housed in intermediate settings. Individuals were evaluated through four experimental sessions (tests). Results indicated that 86% of the Chimfunshi sample was lateralized (48% RH, 38% LH). Furthermore, the sample showed population-level right-handedness in the mean handedness index, in Test 1, Test 2, and the first half of the study (Test 112). Rearing experience did not have an influence on handpreference. Taken together, the two sample (intermediate settings: Chimfunshi and Mona) results indicate a clear right-handedness. In conclusion, this replication and extension shows that (1) the Mona and Chimfunshi chimpanzees are right-handed in certain conditions, (2) the results are consistent with those obtained by Hopkins in captive settings, (3) the humanization of the samples does not affect manual laterality, (4) females are right-handed at population-level, but not males, and (5) these results reinforce the fact that the complexity of the task plays a dominant role in the expression of hand laterality among chimpanzees.     

Asymmetries in body part size, mobility, and usage. Relationship between structure and function

Asymmetries in structure (size) and function (usage or mobility) for the upper and lower face, hands, and feet were investigated in 42 left- and right-handed male and female college students. Size measurements were taken from photographs, mobility was rated from videotapes, and usage was assessed by questionnaire. Size asymmetries were typical, and independent of handedness, but were not consistent across body parts; usage asymmetries varied as a function of handedness. No systematic relationships were found between structure and function.     

Fluctuation and directional asymmetry of the oppositely orientated finger ridge counts in Bulgarians

In a sample from Northeast Bulgaria (500 males, 500 females) fluctuating and directional asymmetries of the radial and ulnar finger ridge-counts were studied, each sex separately and finger-by-finger. Neither the ridge counts nor their fluctuating asymmetries show any considerable sex difference. In contrast, the curves of the ulnar and radial directional asymmetries, each of them being similarly distributed over the digits in both sexes, are contrasted in males and females. One interpretation is that the sex chromosomes exert a considerable effect upon the mediolateral developmental gradients and so cause a set of well expressed sex differences in the directional asymmetries of the ulnar and radial finger ridge-counts.     

Non-genic inheritance of cellular handedness

Ciliates exhibit an asymmetry in arrangement of surface structures around the cell which could be termed handedness. If the usual order of placement of structures defines a 'right-handed' (RH) cell, then a cell with this order reversed would be 'left-handed' (LH). Such LH forms appear to be produced in Tetrahymena thermophila through aberrant reorganization of homopolar doublets back to the singlet condition. Four clones of LH forms were selected and subjected to genetic analysis to test whether this drastic phenotypic alteration resulted from a nuclear genetic change. The results of this analysis indicate that the change in handedness is not due to a genetic change in either the micronucleus or macronucleus. The LH form can, under certain circumstances, revert to the RH form, but typically it propagates itself across both vegetative and sexual generations with similar fidelity. While this analysis does not formally rule out certain possibilities of nuclear genic control involving regulatory elements transmitted through the cytoplasm, when the circumstances of origin and propagation of the LH condition are taken into account direct cortical perpetuation seems far more likely. Here we outline a conceptual framework centred on the idea of longitudinally propagated positional information; the positive evidence supporting this idea as well as further application of the idea itself are presented in the accompanying paper.     

Estrogen therapy affects right hemisphere functioning in postmenopausal women

It has been suggested that hormone therapy (HT) in postmenopausal women differentially affects verbal and visuo-spatial abilities which mainly rely on left hemisphere (LH) and right hemisphere (RH) functioning, respectively. Thus, it seems likely that HT-related effects on cognition are driven by associated hormonal changes and their impact on functional brain organization, and functional cerebral asymmetries (FCAs) in particular. The present study investigated HT-related effects on FCAs in sixty-seven postmenopausal women who received hormone therapy either with estrogen (E) alone (n =  14), an E-gestagen combination (n =  22) or without HT (control group, n =  31). Saliva levels of free E and progesterone (P) were analyzed using chemiluminescence assays. FCAs were measured with the visual half-field (VHF) technique using a word matching and a figural comparison task. In agreement with previous results, a postmenopausal control group showed a left hemisphere (LH) advantage in the verbal task and a right hemisphere (RH) advantage in visuo-spatial processing. In contrast, both HT groups revealed significantly reduced FCAs in the figural comparison task as a result of an E-related decrease in RH performance. The findings suggest that E-therapy in postmenopausal women can affect visuo-spatial abilities by modulating the functional brain organization and RH functioning in particular.     

Genetic associations between lateral signs.

Only a few authors examined several lateral asymmetries in families simultaneously. Seven lateralities (handedness, footedness, eyedness, earedness, hand clasping, arm folding and leg crossing) were examined in a sample of 292 biologically related parent-offspring triads and 36 sibling pairs. Analysis of the family data showed a significant association between parents and children in most lateralities. The frequency of left-sidedness increased with the number of left-sided parents. Only in the case of footedness and hand clasping there are no significant correlations. Additionally we investigated the inter-relationship between the lateralities in the parental generation. There is a relative strong relation especially among the functional asymmetries. The study analysed also the genetic association (linkage) according to McManus & Mascie-Taylor (1979) between seven different lateralized characteristics. It is shown that the lateral asymmetries correlate genetically relatively imperfectly with each other comparing the inter-relationship between the lateralities in the parental generation. This implicates a multigenetical and also multifactorial determination of laterality in human being.     

Inheritance of human fingerprints]

Polygenic threshold model of finger dermatoglyphics inheritance is worked out on the basis of family and population data. According to the model, ulnar loops are subthreshold patterns, which transforms into whorl or arch under the control of SU and SR gene complexes. Epistasis-hypostasis interactions take place between genes of SU and SR complexes. Classification of phenotypes for finger dermatoglyphics is offered and the frequency of these phenotypes in three populational samples of Kiev is studied.     

Digital dermatoglyphic patterns of Eskimo and Amerindian populations: relationships between geographic, dermatoglyphic, genetic, and linguistic distances.

Dermatoglyphic traits have been used to assess population affinities and structure. Here, we describe the digital patterns of four Eskimo populations from Alaska: two Yupik-speaking villages from St. Lawrence Island and two Inupik groups presently residing on mainland Alaska. For a broader evolutionary perspective, these four Eskimo populations are compared to other Inuit groups, to North American Indian populations, and to Siberian aggregates. The genetic structures of 18 New and Old World populations were explored using R-matrix plots and Wright's FST values. The relationships between dermatoglyphic, blood genetic, geographic, and linguistic distances were assessed by comparing matrices through Mantel correlations and through partial and multiple correlations. Statistically significant relationships between dermatoglyphics and genetics, genetics and geography, and geography and language were revealed. In addition, significant correlations between dermatoglyphics and geography, with linguistic variation constant, were noted for females but not for males. These results attest to the usefulness of dermatoglyphics in resolving various evolutionary questions concerning normal human variation.     

Age- and sex-associated variations in the directional asymmetry of rhesus macaque forelimb bones

Several investigators have questioned the significance of handedness as an explanation of directional forelimb asymmetries, yet little has been done to isolate other explanatory factors. In this investigation, we analyze 61 female and 76 male rhesus macaque skeletons for evidence of age- and/or sex-associated variations in ten forelimb bone measurements. All significant directional asymmetries are found to favor the right side. Although some of these asymmetries are found to favor the right side. Although some of these asymmetries are compatible with the interpretation of muscle hypertrophy associated with preferential use of the right forelimb, the overall pattern suggests that age- and sex-related ontogenetic factors deserve equal consideration. Significant sex differences in asymmetry means are present within and across age groups (juveniles, subadults, and adults), and numerous changes in asymmetry with age are also found. A pattern of decreasing asymmetry with age was found in males, with 40% of the ten measures being asymmetrical in juveniles, 30% in subadults, and 20% in adults. Among females, this pattern is reversed. No significant asymmetries were found for juvenile or subadult females, whereas 40% of the measures were asymmetrical in adult females. We conclude that greater consideration of age- and sex-related factors is necessary when drawing samples for the purpose of investigating asymmetries, and an awareness of trait-specific age and sex patterns of variation is necessary when citing forelimb asymmetries in demographically nonrepresentative populations as evidence of handedness or other behavioral asymmetries.     

Lateralization of hand skill in bipolar affective disorder

Diverse strands of evidence suggest that schizophrenia is associated with an excess of left and mixed handedness, reflecting anomalous cerebral lateralization. Genetic studies have indicated a degree of overlap between bipolar disorder (BPD) and schizophrenia. Nevertheless, pattern of handedness and degree of lateralization have not been explicitly tested in BPD. We measured handedness, footedness and relative manual dexterity in a sample of 47 families comprising BPD probands and their bipolar-spectrum and unaffected relatives (N = 240). The BPD I sample (N = 55) was significantly more lateralized on handedness, footedness and relative manual dexterity than their unaffected relatives (N = 66). They were also more lateralized than their relatives with other psychiatric diagnoses. No evidence of excess mixed handedness or footedness was observed in the BPD I sample. We raise the possibility that schizophrenia and BPD I differ in that disproportionate left-hemisphere dominance in BPD I is associated with right-hemisphere dysfunction leading to deficits in emotional regulation. Given our results, we hypothesized that degree of lateralization may be a phenotypic marker or endophenotype for BPD I. We therefore conducted a family-based genetic association analysis with this quantitative trait. Relative hand skill was significantly associated with a functional variant in the catechol-O-methyltransferase gene. We speculate that this polymorphism may influence brain lateralization.     

Did Equity of Reproductive and Maternal Health Service Coverage Increase during the MDG Era? An Analysis of Trends and Determinants across 74 Low- and Middle-Income Countries

Introduction

Despite widespread gains toward the 5^th Millennium Development Goal (MDG), pro-rich inequalities in reproductive health (RH) and maternal health (MH) are pervasive throughout the world. As countries enter the post-MDG era and strive toward UHC, it will be important to monitor the extent to which countries are achieving equity of RH and MH service coverage. This study explores how equity of service coverage differs across countries, and explores what policy factors are associated with a country’s progress, or lack thereof, toward more equitable RH and MH service coverage.

Methods

We used RH and MH service coverage data from Demographic and Health Surveys (DHS) for 74 countries to examine trends in equity between countries and over time from 1990 to 2014. We examined trends in both relative and absolute equity, and measured relative equity using a concentration index of coverage data grouped by wealth quintile. Through multivariate analysis we examined the relative importance of policy factors, such as political commitment to health, governance, and the level of prepayment, in determining countries’ progress toward greater equity in RH and MH service coverage.

Results

Relative equity for the coverage of RH and MH services has continually increased across all countries over the past quarter century; however, inequities in coverage persist, in some countries more than others. Multivariate analysis shows that higher education and greater political commitment (measured as the share of government spending allocated to health) were significantly associated with higher equity of service coverage. Neither country income, i.e., GDP per capita, nor better governance were significantly associated with equity.

Conclusion

Equity in RH and MH service coverage has improved but varies considerably across countries and over time. Even among the subset of countries that are close to achieving the MDGs, progress made on equity varies considerably across countries. Enduring disparities in access and outcomes underpin mounting support for targeted reforms within the broader context of universal health coverage (UHC).     

Effects of intraventricular brain injections of neurotransmitters on colonic temperature in morphine-tolerant rats

A sensitive and specific radioimmunoassay for LH-releasing hormone (LHRH) was developed. Using a specific antibody we have attempted to define or dissociate a separate FSHRH, antigenically distinct from LHRH. In an $\text{in vitro}$ system, LH release by hypothalamic extract was inhibited by a certain dose of LHRH antiserum but FSH release was not affected. Diurnal patterns of LHRH, FSH and prolactin were studied but no clear cyclic changes were shown. LHRH and LH levels in the serum were completely dissociated. We suggest that negative feedback systems play a more critical role than hypothalamic LHRH in the release of LH.     

Front Cover

This review highlights the scientific advances concerning the origins of human right‐handedness and language (speech and gestures). The comparative approach we adopted provides evidence that research on human and non‐human animals’ behavioural asymmetries helps understand the processes that lead to the strong human left‐hemisphere specialisation. We review four major non‐mutually exclusive environmental factors that are likely to have shaped the evolution of human and non‐human primates’ manual asymmetry: socioecological lifestyle, postural characteristics, task‐level complexity and tool use. We hypothesise the following scenario for the evolutionary origins of human right‐handedness: the right‐direction of modern humans’ manual laterality would have emerged from our ecological (terrestrial) and social (multilevel system) lifestyle; then, it would have been strengthened by the gradual adoption of the bipedal stance associated with bipedal locomotion, and the increasing level of complexity of our daily tasks including bimanual coordinated actions and tool use. Although hemispheric functional lateralisation has been shaped through evolution, reports indicate that many factors and their mutual intertwinement can modulate human and non‐human primates’ manual laterality throughout their life cycle: genetic and environmental factors, mainly individual sociodemographic characteristics (e.g., age, sex and rank), behavioural characteristics (e.g., gesture per se and gestural sensory modality) and context‐related characteristics (e.g., emotional context and position of target). These environmental (evolutionary and life cycle) factors could also have influenced primates’ manual asymmetry indirectly through epigenetic modifications. All these findings led us to propose the hypothesis of a multicausal origin of human right‐handedness.