Handedness and the side on which pharyngeal pouches occur.

Pharyngeal pouches present far more commonly on the left side of the neck than the right. Sixty one patients with a history of pharyngeal pouch were questioned about their handedness and about whether they had had symptoms or signs predominantly on one side of the neck before receiving treatment. There was a highly significant association between handedness and pharyngeal pouches on the opposite side of the neck. It is suggested that this is the reason for the rarity of right sided pouches.     

The difference between the mineral content and the width of the radius on each side and its significance for handedness determination of skeletal material

The objective of our work was to investigate whether the side-different use of the upper extremities due to handedness produces detectable differences in bone-mineral content (BMC) and bone width (BW). For this purpose 251 recent individuals whose handedness was established, were examined by means of the 125I-photon-absorption technique. Highly significant right-left differences in BMC and BW were found on the midshaft and distal radius. Discrimination functions based on BMC and BW were carried out, allowing for the classification into the appropriate handedness categories. Applying the same method we tried to diagnose the handedness of the skeletal material of 40 medieval and 27 neolithic individuals.     

Factor Analysis of Multiple Measures of Hand Use in Captive Chimpanzees: An Alternative Approach to the Assessment of Handedness in Nonhuman Primates

We tested whether chimpanzee handedness could be characterized as either unidimensional or multidimensional when considered across multiple measures of hand use. We determined for each of 6 different tasks in a sample of 105 captive chimpanzees hand preferences, and subjected the individual hand preference scores to a factor analysis. Five of the 6 tasks loaded on two separate factors that accounted for 54% of the variance. To assess population-level handedness, we calculated handedness indices for the loadings on each factor, for the item loadings across all factors, and for all tasks including ones that did not load on any factor. There is significant population-level right handedness for all 4 indices, which suggests that chimpanzee handedness is multidimensional and not task specific.     

Study on pottical type, palmar and plantar digital formulae, hand clasping, arm folding, handedness, leg folding and stride type in the Daur population, China

The pottical type, palmar and plantar digital formulae, hand clasping, arm folding, handedness, leg folding and stride type have been investigated on a sample of 143 male and 160 female students of the Daur population of Molidawa Banner, Inner Mongolia. The results of this study are the following: 1. the frequency of the hyperextensive pottical type is 49.17%, the relative length of index over annularis 12.21%, right hand clasping 45.87%, right arm folding 49.50%, right handedness 94.39%, right leg folding 72.28% and right stride type 44.88%, 2. pottical type, hand clasping, handedness, leg folding and stride type do not show significant sex differences, 3. there are some relations between hand clasping and arm folding as well as between arm folding and stride type, 4. compared with other population groups, the Daur population shows a low frequency of right hand clasping, a moderate frequency of right arm folding and a low frequency of left handedness.     

Competitiveness,gender and handedness

We conduct an intercultural experiment in three locations on three different continents to elicit competitiveness and study whether individual differences in competitiveness are related to handedness. Being a “lefty” (i.e., having either a dominant left hand or a dominant left foot) is associated with neurological differences which are determined prenatally, and can therefore be seen as a proxy for innate differences. In large-scale data with incentivized choices from 3664 participants from India, Norway and Tanzania, we find a significant gender gap in competitiveness in all cultures. However, we find inconsistent results when comparing the competitiveness of lefties and righties. In north-east India we find that lefties of both genders are significantly more competitive than righties. In Norway we find that lefty men are more competitive than any other group, but women’s competitiveness is not related to handedness. In Tanzania, we find no relationship between handedness and the competitiveness of either gender. The merged data show weak evidence of a positive correlation between being a lefty and competitiveness for men, but no such evidence for women. Thus, our data provide suggestive but not robust evidence that individual and gender differences in competitiveness are partially determined by innate factors, where innate factors are proxied by the complex, prenatally shaped trait of handedness.     

Bilateral detection thresholds in dextrals and sinistrals reflect the more sensitive side of the nose, which is not lateralized [published erratum appears in Chem Senses 1998 Dec;23(6):761]

Several fundamental questions remain enigmatic concerning human olfactory sensitivity, including (i) whether detection threshold differences exist between the two sides of the nose (and, if so, whether such differences are influenced by handedness) and (ii) whether bilateral (i.e. binasal) stimulation leads to lower thresholds than unilateral stimulation (and, if so, whether the degree of facilitation is inversely related to general olfactory ability). In this study, and well-validated single staircase procedure was used to establish bilateral and unilateral detection thresholds for the cranial nerve I stimulant phenyl ethyl alcohol in 130 right- and 33 left-handed subjects. No differences in sensitivity between the left and right sides of the nose were observed in either group. Bilateral thresholds were lower, on average, than unilateral thresholds when the latter were categorized in terms of left and right nares. However, the bilateral thresholds did not differ significantly from those of the side of the nose with the lower threshold. Overall smell ability, as measured by the University of Pennsylvania Smell Identification Test, did not interact with any of the test measures. These data imply that (i) the left and right sides of the nose do not systematically differ in detection threshold sensitivity for either dextrals or sinistrals and (ii) if central integration of left:right olfactory threshold sensitivity occurs, its effects do not exceed the function of the better side of the nose.      

Cortical activations in humans grasp-related areas depend on hand used and handedness

Background

In non-human primates grasp-related sensorimotor transformations are accomplished in a circuit involving the anterior intraparietal sulcus (area AIP) and both the ventral and the dorsal sectors of the premotor cortex (vPMC and dPMC, respectively). Although a human homologue of such a circuit has been identified whether activity within this circuit varies depending on handedness has yet to be investigated.

Methodology/Principal Findings

We used functional magnetic resonance imaging (fMRI) to explicitly test how handedness modulates activity within human grasping-related brain areas. Right- and left-handers subjects were requested to reach towards and grasp an object with either the right or the left hand using a precision grip while scanned. A kinematic study was conducted with similar procedures as a behavioral counterpart for the fMRI experiment. Results from a factorial design revealed significant activity within the right dPMC, the right cerebellum and AIP bilaterally. The pattern of activity within these areas mirrored the results found for the behavioral study.

Conclusion/Significance

Data are discussed in terms of an handedness-independent role for the right dPMC in monitoring hand shaping, the need for bilateral AIP activity for the performance of precision grip movements which varies depending on handedness and the involvement of the cerebellum in terms of its connections with AIP. These results provide the first compelling evidence of specific grasping related neural activity depending on handedness.     

Handedness and longevity: archival study of cricketers.

OBJECTIVE--To test whether handedness is associated with a change in longevity. DESIGN--Archival survey. SETTING--British Isles. SUBJECTS--All first class cricketers born before 1961 whose bowling hand was specified (right, n = 5041; left, n = 1132) in a comprehensive encyclopaedia. MAIN OUTCOME MEASURES--Bowling hand and life span. RESULTS--Regression analysis of the 5960 players born between 1840 and 1960 (3387 dead, 2573 alive) showed no significant relation between mortality and handedness (P = 0.3). Left handedness was, however, associated with an increased likelihood of death from unnatural causes (P = 0.03, log hazard 0.37, 95% confidence interval 0.04 to 0.70). This effect was especially related to deaths during warfare (P = 0.009, log hazard 0.53, 0.13 to 0.92). CONCLUSION--Left handedness is not, in general, associated with an increase in mortality.     

Breast volume measurement of 248 women using biostereometric analysis

A study of volumes of the right and left breasts of 248 subjects was undertaken using biostereometric analysis. This measurement technique uses close-range stereophotogrammetry to characterize the shape of the breast and is noncontact, noninvasive, accurate, and rapid with respect to the subject involvement time. Volumes and volumetric differences between breast pairs were compared, using chi-square tests, with handedness, perception of breast size by each subject, age, and menstrual status. No significant relationship was found between the handedness of the subject and the larger breast volume. Several groups of subjects based on age and menstrual status were accurate in their perception of breast size difference. Analysis did not confirm the generally accepted clinical impression of left breast volume dominance. Although a size difference in breast pairs was documented, neither breast predominated.     

Baseline cortisol levels and social behavior differ as a function of handedness in marmosets (Callithrix jacchus)

Population hand preferences are rare in nonhuman primates, but individual hand preferences are consistent over a lifetime and considered to reflect an individual's preference to use a particular hemisphere when engaged in a specific task. Previous findings in marmosets have indicated that left‐handed individuals tend to be more fearful than their right‐handed counterparts. Based on these findings, we tested the hypotheses that left‐handed marmosets are (a) more reactive to a social stressor and (b) are slower than right‐handed marmosets in acquiring a reversal learning task. We examined the hand preference of 27 male and female marmosets (ages of 4–7 years old) previously tested in a social separation task and a reversal learning task. Hand preference was determined via a simple reaching task. In the social separation task, monkeys were separated from their partner and the colony for a single 7‐hr session. Urinary cortisol levels and behavior were assessed at baseline, during the separation and 24 hr postseparation. Hand preferences were equally distributed between left (n = 10), right‐handed (n = 10), and ambidextrous (n = 7) individuals. The separation phase was associated with an increase in cortisol levels and behavioral changes that were similar across handedness groups. However, cortisol levels at baseline were positively correlated with right‐handedness, and this relationship was stronger in females than in males. In addition, the occurrence of social behaviors (pre‐ and postseparation) was positively correlated with right‐handedness in both sexes. Baseline cortisol levels did not correlate significantly with social behavior. Acquisition of the reversals was poorer in females than males but did not differ as a function of handedness. We conclude that (a) both stress reactivity and cognitive flexibility are similar across handedness groups and (b) left‐handers exhibit less social behavior and have lower basal cortisol levels than ambidextrous and right‐handed subjects. The underlying causes for these differences remain to be established.     

The development of handedness in left/right asymmetry

The development of handed asymmetry requires a special mechanism for consistently specifying a difference between left and right sides. This is to be distinguished from both random asymmetry, and from those left/right differences that are mirror symmetrical. We propose a model for the development of handedness in bilateral animals, comprising three components. (i) A process termed conversion, in which a molecular handedness is converted into handedness at the cellular level. A specific model for this process is put forward, based on cell polarity and transport of cellular constituents by a handed molecule. (ii) A mechanism for random generation of asymmetry, which could involve a reaction-diffusion process, so that the concentration of a molecule is higher on one side than the other. The handedness generated by conversion could consistently bias this mechanism to one side. (iii) A tissue-specific interpretation process which responds to the difference between the two sides, and results in the development of different structures on the left and right. There could be direct genetic control of the direction of handedness in this model, most probably through the conversion process. Experimental evidence for the model is considered, particularly the iv mutation in the mouse, which appears to result in loss-of-function in biasing, and so asymmetry is random. The model can explain the abnormal development of handedness observed in bisected embryos of some mammalian, amphibian and sub-vertebrate species. Spiral asymmetry, as seen in spiral cleavage and in ciliates, involves only conversion of molecular asymmetry to the cellular and multicellular level, with no separate interpretation step.     

HANDEDNESS IN THE BROWN-THROATED PARAKEET ARATINGA PERTINAX EST RELATION WITH SKELETAL ASYMMETRY

Observations on 56 specimens of Aratinga pertinax when bringing food to the beak prove that 28 birds were right-handed while the other 28 were left-handed. A biometric analysis reveals a slight departure from bilateral symmetry in hindlimb bones in close relationship with handedness. In the right-handed birds, there is a significant predominance in the length of the right hindlimb as a whole and all right limb segments. The opposite holds true in left-handed parrots (except for the femur). Right-handed birds are in general more highly asymmetrical than left-handed ones. There is a positive correlation between asymmetry of homologous segments of a pair of limbs and the asymmetry of the other segments of the same pair of limbs. The absence of significant negative correlations between bilateral differences of the different segments of a limb indicates that departures from bilateral symmetry tend to affect the limb as a whole, and thus is not in agreement with the rule of compensating variations.     

Brief communication: Captive gorillas are right‐handed for bimanual feeding

Predominance of right‐handedness has historically been considered as a hallmark of human evolution. Whether nonhuman primates exhibit population‐level manual bias remains a controversial topic. Here, we investigated the hypothesis that bimanual coordinated activities may be a key‐behavior in our ancestors for the emergence and evolution of human population‐level right‐handedness. To this end, we collected data on hand preferences in 35 captive gorillas (Gorilla gorilla) during simple unimanual reaching and for bimanual coordinated feeding. Unimanual reaching consisted of grasping food on the ground, while bimanual feeding consisted of using one hand for holding a food and processing the food item by the opposite hand. No population‐level manual bias was found for unimanual actions but, in contrast, gorillas exhibited a significant population‐level right‐handedness for the bimanual actions. Moreover, the degree of right‐handedness for bimanual feeding exceeds any other known reports of hand use in primates, suggesting that lateralization for bimanual feeding is robust in captive gorillas. The collective evidence is discussed in the context of potential continuity of handedness between human and nonhuman primates. Am J Phys Anthropol 2010. © 2009 Wiley‐Liss, Inc.     

Genetic and environmental contributions to the expression of handedness in chimpanzees (Pan troglodytes)

Most humans are right‐handed and, like many behavioral traits, there is good evidence that genetic factors play a role in handedness. Many researchers have argued that non‐human animal limb or hand preferences are not under genetic control but instead are determined by random, non‐genetic factors. We used quantitative genetic analyses to estimate the genetic and environmental contributions to three measures of chimpanzee handedness. Results revealed significant population‐level handedness for two of the three measures—the tube task and manual gestures. Furthermore, significant additive genetic effects for the direction and strength of handedness were found for all three measures, with some modulation due to early social rearing experiences. These findings challenge historical and contemporary views of the mechanisms underlying handedness in non‐human animals.     

Hand dominance and bilateral asymmetry in the structure of the second metacarpal

Bilateral asymmetry in the structure of the second metacarpal was examined in relation to functional hand dominance in a large, clinically nonselected, healthy population sample from the Baltimore Longitudinal Study of Aging. Bilateral bone measurements were made from anteroposterior hand radiographs of a total of 992 individuals, 609 males and 383 females, with an age range of 19–94 years. Hand dominance was determined on the basis of personal impression. Total width and medullary width at the midshaft of the second metacarpal were measured to 0.05 mm using a Helios caliper. These two measurements were used to derive cortical thickness, cortical bone area, periosteal (total) area, medullary area, percent cortical area, and the second moment of area in the mediolateral plane. In both right and left-handed individuals, statistically significant side differences were found in the calculated bone areas and the second moment of area, with the dominant hand being larger. Cortical thickness did not show significant side-related differences for either handedness. These results show that functional handedness leads to periosteal and endosteal expansion of the second metacarpal cortex on the dominant side, increasing bone strength without increasing cortical thickness. This is the first time this pattern of asymmetry has been reported in left-handers as well as right-handers. Our results argue for the primacy of environmental (mechanical) effects in determining bilateral asymmetry of limb bone structural properties. © 1994 Wiley-Liss, Inc.     

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.     

Directional asymmetry in the forelimb of Macaca mulatta

Asymmetry was investigated in the forelimbs of 150 rhesus monkey (Macaca mulatta) skeletons using measurements of right and left humerii, radii, ulnae, second metacarpals, and femora. Seven of the ten forelimb dimensions were larger on the right than on the left side. Paired t-tests revealed that the mean of the right side was significantly larger than that for the left for two measurements of the ulna and two of the humerus. No measurement was significantly larger on the left than on the right side. These results indicate a small but significant asymmetry in the forelimb bones of rhesus monkeys and, as is the case for humans, the direction of asymmetry favors the right side. Our findings are consistent with an interpretation of hypertrophy of certain muscles and opens the question of whether rhesus monkeys preferentially use their right forelimbs for manipulative tasks that require manual dexterity, as is the case for humans. These forelimb skeletal asymmetries are discussed in light of the recent literature on cortical asymmetry and handedness in nonhuman primates.     

Actigraphic Investigations On The Activity‐Rest Behavior Of Right‐ and Left‐Handed Students

The aim of this study was to explore differences between left‐and right‐handed subjects in sleep duration. Sleep and activity patterns were continuously registered for 12 days using actometers on 20 left‐handed and 20 right‐handed medical students in Berlin. Handedness was determined by a modified version of the Edinburgh handedness inventory. Each participant wore one actometer on each wrist. Actiwatch® Sleep Analysis Software (CNT, UK) was used to evaluate the data, and statistical calculations were performed with a non‐parametric variance analysis. A significant difference in mean sleep duration between left‐handers (7.9 h) and right‐handers (7.3 h) was determined (p=0.025 for measurement made on the dominant hand and p=0.013 for ones made on the non‐dominant hand). In contrast, the maximal phase of daily activity (acrophase) did not show any difference between the two groups. The difference in sleep duration might be caused by either the greater effort required for left‐handers to cope in a right‐handed world or by structural brain differences.     

Chimpanzee right-handedness reconsidered: Evaluating the evidence with funnel plots

Evidence for population-level right-handedness in nonhuman primates seems inconsistent and contradictory, and many hypotheses have been advanced to account for this volatility. Funnel plots (scatter plots of percent right-hand use vs. sample size) offer a straightforward graphical technique for assessing: 1) the strength and consistency of handedness, 2) whether variability is consistent with normal sampling variation, and 3) how likely reports of statistically significant handedness might have arisen due to chance (i.e., type I error). They are informative for both within- and among-population variation. Reexamination of within-population variation from a detailed and widely cited study reporting significant population-level right-handedness in 140 individual captive chimpanzees (Hopkins [1994] Dev. Psychobiol. 27:395-407) revealed several puzzling patterns: 1) funnel plots showed higher percent right-hand use among individuals for which fewer observations were recorded, 2) when individuals with fewer than 25 observations were excluded, statistical support for population-level right-handedness either became marginal (P = 0.043, when computed as average percent use of the right hand) or disappeared (P = 0.62, when computed as proportion of individuals using the right hand more than the left, whether they did so significantly or not), and 3) the proportion of statistically ambilateral chimpanzees actually increased with increasing number of observations per individual, rather than decreased as would be expected for true population-level right-handedness. In addition, funnel plots of among-population variation from an earlier meta-analysis (McGrew and Marchant [1997] Yrbk. Phys. Anthropol. 40:201-232) suggested that the four reports of significant right-handedness, out of 37 estimates from 14 studies, were likely those that achieved statistical significance simply due to chance. Funnel plots, and the more refined statistical tests they suggest, confirm that the current evidence for population-level right-handedness in chimpanzees remains equivocal.     

Relative growth,morphological sexual maturity,heterochely, and handedness in Panopeus occidentalis (Brachyura,Panopeidae)

Studies on relative growth and sexual maturity are important to understand the reproductive biology of a species. The aims of this study were to determine the relative growth and to estimate the size of Panopeus occidentalis at morphological sexual maturity, as well as to confirm whether this species demonstrates heterochely or handedness. Individuals were collected every two months from March 2013 to July 2014 in the intertidal estuarine zone of Cananeia, São Paulo, Brazil. The following measurements were taken: carapace width (CW), carapace length (CL), right and left cheliped propodus length (CPL), right and left cheliped propodus height (CPH), right and left cheliped propodus width (CPW), abdomen width (AW), and first pleopod length (FPL). The morphometric relationship used to estimate the size at morphological sexual maturity were CW vs. AW for females and CW vs. FPL for males; these comparisons yielded estimated CW values of 15.60 mm and 16.67 mm, respectively. Heterochely was observed but handedness was not present. The species has a major cheliped on one side, but the side is not constant. This study provides the first insights on the relative growth, sexual maturity, heterochely, and handedness on a population of P. occidentalis in a conserved area.