Handedness related differences in the intracranial fluid spaces in healthy adults

Abstract

Purpose: Our study aimed to determine the possible differences in linear measurements and linear indices values of intracranial fluid spaces (IFS) between right- and left-handed adults.

Methods: This work has been carried out on 148 subjects (72 men and 76 women). In the study, 88 right-handers and 60 left-handers were included. Forty of the right-handers were male, 48 were female, and 32 of the left-handers were male, and 28 were female. The ages were between 20 and 50?years. Linear measurements were obtained based on magnetic resonance imaging (MRI) studies. A 1.5-T MRI scanner was used to obtain axial images. The ten parameters were estimated from MRI scans.

Results: There was no correlation between parameters and age. In our study, interestingly, as can be seen from the tables, most of the parameters with statistically significant differences were higher in favour of left-handed subjects. In most of the linear measurement results, IFS values of the right hemisphere in right-handers, and the left hemisphere in left-handers were higher. Similar results were found in favour of the left-handed in most of the linear ventricular indices.

Conclusion: Linear measurements and linear indices values of IFS were mostly higher in left-handers than in right-handed individuals.     

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.     

Manual asymmetry in children is related to parameters of early development and familial sinistrality

The possible relationships of the manual preference (handedness) of primary school children with the parameters of their development (prenatal and during the first two years of life) and the existence of left-handed close relatives were analyzed. The percentage of left-handers was higher among children born after some complications during pregnancy or delivery and among children having left-handed relatives. The effects of the two factors were not correlated. It has also been found that the infants having left-handed first-degree relatives were, on average, larger than other ones.     

Directional asymmetry of body dimensions among white adolescents

Asymmetry of paired dimensions has been recognized as a methodological problem in anthropometry and more recently as an indicator of environmental stress. This study seeks to determine the extent of directional asymmetry for some of the measurements commonly made in anthropometry. Upper arm circumference, biepicondylar breadth, triceps and subscapular skinfolds, bicondylar breadth of the femur, and calf circumference were measured on right and left sides among 135 white adolescents from suburban Philadelphia. Handedness (right or nonright) was subject-assessed. Body composition was estimated through underwater weighing. Asymmetry was evaluated using a paired t test. Arm measurements are significantly asymmetric in favor of the right side; subscapular skinfolds and leg measurements are not significantly asymmetric. Among the sample of right-handed subjects (n = 116), upper arm circumference and biepicondylar breadth were significantly larger on the right side, and, among the males of this subsample, triceps was as well. The nonright-handed subjects (n = 19) did not show statistically significant asymmetry. Asymmetry was negatively but weakly related to body composition. These results are consistent with an explanation in terms of preferred use of one side of the body and consequent muscle hypertrophy, but an adequate test of this explanation requires hypothesis testing in larger samples of nonright-handed subjects.     

Heterochely and handedness in the shore crab Carcinus maenas (L.) (Crustacea: Brachyura)

A large sample ofadult male Carcinus maenas was 79% right-handed and 21% left-handed. A separate sample of 207 intact adult males was divided into left-handed and right-handed crabs and four measurements were taken from all major and minor chelae. Correlation and regression analyses against carapace width on log-transformed data showed that major chelae of right-handed crabs grow proportionately higher with increasing size and the ideal mechanical advantage increases; concurrently, the fingers of the minor chelae grow proportionately longer. The data for left-handed crabs showed greater variability, especially for minor chelae, providing evidence for the concept that left-handedness arises by reversal of handedness following loss of the major chela from the right-hand side. Records of handedness in large samples of non-ocypodid heterochelous brachyuran crabs show a preponderance of right-handedness.     

Sex difference in chimpanzee handedness

Chimpanzees at Mahale, Tanzania, show strong individual hand preferences when they use bimanual actions in processing the fruit of Saba florida and Citrus lemon. The direction of hand preference differs between the sexes: most males are left-handed, whereas most females are right-handed. Monkeys and apes are considered to lack "handedness," in the sense of a population mode of left- or right-hand preference; they are normally ambidextrous. Indeed, strong individual preferences were previously seldom found in natural tasks. We propose that lateralization of manual actions becomes advantageous in bimanual tasks, which involve role differentiation between the hands and a need to combine power and precision. If the pattern of lateralization found here reflects the ancestral state, common to chimpanzees and humans, this may explain why, in modern humans, women tend more strongly to be right-handed than men, who include a larger minority of left-handers.     

Functional asymmetry in the face.

The possible existence of one-sided dominance in the face, similar to the phenomena of handedness and footedness, has been investigated by studying smiling pattern, movements of the angles of mouth, winking, platysma contraction, raising and everting the upper lip with dilatation of the nostril, and vertical wrinkling of the forehead, on 300 right-handed and 30 left-handed persons. The conclusions are as follows: 1. The large majority of persons investigated do not use the two sides of face equally. 2. Facial ambilaterality is a rare feature. 3. There is no clear-cut correlation between handedness and the dominant side of the face. 4. The greater percentage (58.66%) of right-handed persons show a left-sided smile and find it more convenient to perform almost all exercises with the left side of the face. A still greater percentage (73.33%) of left-handed persons shows a right-sided smile and a better performance of all exercises with the right side of the face. The contralateral relationship of handedness to the dominant side of the face is significant in the right-handed and more so, in the left-handed persons.     

Handedness and socioeconomic status in an urban population in Uzbekistan

The persistence of left-handers in every human population studied to date is an evolutionary puzzle in light of evidence of survival costs associated with left-handedness. Associations between left-handedness and socioeconomic advantages have been observed in Western countries and could provide left-handers fitness benefits through higher survival chances and greater reproductive success. We aimed to explore the generality of this result in another culture. For this purpose, we investigated several socioeconomic status indicators and the number of children alive for 917 men and women in Uzbekistan and compared results for two different measures of handedness: hand preferences for writing and for knife use. Among both men and women, left-handed writers were significantly more likely to own a car, own a washing machine and have a bank account. Left-handed women (using both measures) had a higher income than right-handed women. Among men, left-handers for knife use had a higher income than right-handers. The results of our study suggest that the previously observed socioeconomic advantage of left-handers in Western populations also applies to non-Western populations, at least in the urban environment studied. However, we did not detect any difference in the number of children. We discussed how the frequency-dependent socioeconomic status advantage could be responsible for the persistence of left-handers throughout human evolution.     

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.     

Morphogenetic variability and handedness in Montenegro and Serbia

This study tries to establish correlations between the types of handedness and several morphophysiological characteristics, controlled by one or a small number of genes with alternative dominant recessive manifestation. The population-genetic homozygosity degree study includes the analysis of the presence, distribution and individual traits combination in left-handed and right-handed persons. It was conducted at three localities in two states, Serbia (SRB) and Montenegro (MNE). Our hypothesis is that a possible genetic load due to increased recessive homozygosity, being a potential population-genetic parameter of left-handedness manifestation, may cause some change in other morpho-physiological characters. The average proportion of 23 studied homozygously-recessive characters (HRC’s) was similar among observed left-handed individuals in the studied localities. It varied from 10.5 ± 0.4 in Serbia to 10.7 ± 0.3 in MNE. The differences were somewhat bigger among right-handed persons, varying from 8.7 ± 0.3 in MNE to 9.1 ± 0.3 HRC’s in Serbia. However, in all localities the average homozygosity was significantly higher among left-handed school children. The number of HRC’s among 400 individuals varied from 2 to 16 among right-handed and from 4 to 19 among left-handed persons. There were no differences in scholar scores between left-handed and right-handed children, although small differences were found between two state samples.     

Paradoxical bilateral asymmetry in bone size and bone mass in the hand

Among 227 chronic renal disease patients, micrometer caliper radiogrammetric measurements of the second metacarpal at midshaft showed the right metacarpal to be larger (with greater bone area) and with a greater cortical area than the left second metacarpal, both in 208 right-handed individuals and in 19 left-handed individuals. This direction of asymmetry was individually characteristic of the majority of individuals, whether right-handed, left-handed or ambidextrous.     

Development of the system of cognitive functions in right- and left-handed boys aged six to seven years: A study taking into consideration specific features of early ontogeny

Characteristics of early ontogeny and the formation of cognitive functions of left-and right-handed boys six to seven years of age have been studied with the genesis of handedness taken into account. A comparative analysis of cognition in right-and left-handed children has been performed using a unified approach to the history of early ontogeny with special emphasis on cognitive functions. The negative effect of pathological pregnancies and births, as well as disturbances in early ontogeny, on the development of cognitive functions in both left-and right-handed boys has been shown. The most “vulnerable” functions in right-handed boys with a history of various pathologies are the organization of activity and visuospatial perception; in left-handed boys, these are fine motor skills and speech development. In the absence of pathologies in the medical history, significantly higher indices of the organization of activity and visuomotor coordination have been found in right-handed boys and significantly higher indices of visuospatial perception, in left-handed boys.     

The AEP T-complex to synthesised musical tones: left-right asymmetry in relation to handedness and hemisphere dominance

Auditory evoked potentials were recorded to onset and offset of synthesised instrumental tones in 40 normal subjects, 20 right-handed for writing and 20 left-handed. The majority of both groups showed a T-complex which was larger at the right temporal electrode (T4) than the left (T3). In the T4-T3 difference waveforms, the mean potential between latencies of 130 and 165 ms was negative in all right-handed subjects except two for whom the waveforms were marginally positive-going. Amongst the left-handers, however, this converse asymmetry was seen in 7 subjects, 5 of them more than 2 standard deviations from the mean of the right-handed group. The degree of asymmetry was not significantly correlated with the degree of left-handedness according to the Edinburgh Handedness Inventory. Asymmetry of the T-complex to instrumental tones appears to reflect the lateralisation of auditory `musical' processing in the temporal cortex, confirming evidence from other sources including PET that this is predominantly right-sided in the majority of individuals. The proportion of left-handers showing the converse laterality is roughly in accordance with those likely to be right-hemisphere-dominant for language. If linguistic and `musical' processes are consistently located in opposite hemispheres, AEPs to complex tones may prove a useful tool in establishing functional lateralisation.     

Developmental origins of variation in human hand preference

Though right-handedness is a prominant characteristic within all human societies, a substantial and stable proportion of individuals are left-handed. Any comprehensive approach to the origin of variation in handedness must account for substantial evidence that left-handedness is associated with reduced fitness, neurodevelopmental disorders, and reduced neuroanatomical asymmetry. In this paper we investigate the hypothesis that developmental instability in early fetal development underlies variation in handedness. In two studies we note an increased incidence of minor physical anomalies (MPAs) and fluctuating asymmetries in both left-handers and extreme right-handers. Moreover, extreme right-handers were more apt to have left-handed parents than moderate right-handers. These data suggest that deviation from moderate right-handedness reflect imprecise expression of a near-universal design due to developmental instability. Preliminary attempts to elucidate the mechanisms underlying developmental instability suggest that both polygenic homozygosity and particular HLA alleles may be important factors. These observations are discussed with respect to current genetic theories of handedness and human evolution.     

A developmental model for predicting handedness frequencies in crabs

Brachyuran crabs develop handedness in at least two different ways. Some crabs, such as Cancer productus, become heterochelous through use-induced differences in claw growth. Other crab species, for instance Carcinus maenas, appear to have a genetic predisposition towards right handedness. In this latter case, however, handedness reversal may take place following autotomy of the major claw. Thus, in C. maenas, and other species with this developmental strategy, younger cohorts are strongly biased towards right-handed individuals and the frequency of left-handedness increases with each subsequent moult. In the absence of differential mortality the ratio of left-handed to right-handed crabs in a given population should be predictable if the frequencies of right and left claw loss are known for different stages in the life history. Here, we develop a simple mathematical model for predicting handedness in crabs under the Carcinus-model of claw ontogeny and apply it to two species with very different ecologies and life histories; the green crab (Carcinus maenas (L.)) and the Trinidadian mountain crab (Eudaniela garmani (Rathburn)). The predicted and observed handedness frequencies were in complete concordance for the early intermoults of both species but significantly deviated in mature C. maenas where left-handed individuals were under-represented in the population. These results are discussed in the context of the evolution and functional significance of claw autotomy and handedness in crabs.     

Corpus callosum morphology in capuchin monkeys is influenced by sex and handedness

Sex differences have been reported in both overall corpus callosum area and its regional subdivisions in humans. Some have suggested this reflects a unique adaptation in humans, as similar sex differences in corpus callosum morphology have not been reported in any other species of primate examined to date. Furthermore, an association between various measurements of corpus callosum morphology and handedness has been found in humans and chimpanzees. In the current study, we report measurements of corpus callosum cross-sectional area from midsagittal MR images collected in vivo from 14 adult capuchin monkeys, 9 of which were also characterized for hand preference on a coordinated bimanual task. Adult females were found to have a significantly larger corpus callosum: brain volume ratio, rostral body, posterior midbody, isthmus, and splenium than adult males. Left-handed individuals had a larger relative overall corpus callosum area than did right-handed individuals. Additionally, a significant sex and handedness interaction was found for anterior midbody, with right-handed males having a significantly smaller area than right-handed females. These results suggest that sex and handedness influences on corpus callosum morphology are not restricted to Homo sapiens.     

The relationship of handedness to asymmetry in the occlusal morphology of first permanent molars.

Handedness has been shown to be related to a number of systematic asymmetries in body dimensions, dermatoglyphic patterns and cerebral morphology. The aim here was to compare linear and angular tooth crown asymmetries of the permanent molars in healthy right-handed and left-handed subjects. The material comprised 27 children with recorded concordant left-side dominance of hand, eye and foot. The controls were an age- and sex-matched group with right side dominance. The material is based on the Collaborative Perinatal Project where detailed medical records and the dentitions, including accurate dental impressions, of over two thousand American children were examined in the USA in the sixties. Machine vision technique was used to obtain accurate three-dimensional information from the occlusal surfaces of the first permanent upper and lower molars. The directional asymmetry values of angular measurements of mandibular first molars showed evidence of asymmetry of opposite direction between the two examined groups. The results indicate that occlusal morphology of first permanent molars may be affected by handedness, and this tendency is most evident in the angular measurements of the mandibular molars. Fluctuating asymmetry did not differ significantly between the examined groups.     

On the handedness of Japanese monkeys

Forty-one monkeys living on the Koshima Island were tested for handedness by throwing a peanut 10 or 20 times toward each subject and recording which hand was used to pick it up. Handedness was judged at the 5% level of confidence. Animals showing no preference for the left or right hand after 20 trials were considered to be ambidextrous. The following distribution of handedness was found: left-handed, 17 (41%); right-handed, 8 (20%); ambidextrous, 16 (39%). These findings were compared with other studies on the handedness of Japanese monkeys. Handed monkeys outnumber the ambidextrous ones and the left-handed monkeys outnumber the right-handed ones. The characteristic distribution of handedness was shown to be irrespective of troop. By looking over the data from these different sources, the proportions of the left-handed, the ambidextrous, and the right-handed in Japanese monkeys were estimated at 39%, 33%, and 28% respectively. The method used in this study was compared withKawai's catching behavior and reasons for disagreement between judgments of handedness were discussed.     

Unilateral injury of sensorimotor cortex of the dominant or subdominant hemispheres of rats-mothers and emotional behavior of their offsprings in the "open field"

Neurohumoral disorders in mothers caused by brain injury, infection, hypoxia, and other pathological factors result in motor and psychoemotional disorders in children. Emotional behavior of 30-day-old offsprings of female rats with unilateral sensorimotor brain injury was studied in the "open field". Individual behavior was estimated (the probability of certain acts and significant transfers between them). Behavioral disorders in rat offsprings depended on the side (left of right) of mother's brain injury and "handedness". The right-side mother's injury turned to be more deleterious. Behavioral alterations were stronger in offsprings of ambidextral and left-handed females than in those born by right-handed males with the same sensorimotor injury.