Metric studies of the dermal ridges of the palm in relation to handedness

Palm prints of 394 right-handers and 356 non-right-handers (left-handers and ambidexters) were evaluated regarding distance ad, ulnar shift, and relative horizontal triradius distance. Comparison between handedness groups produced some significant differences. The "graded distinction of dermatoglyphic traits" which was found in an earlier study has been confirmed. It has been suggested a modification of terminology for the position of axial triradii.     

Psychophysiological reactivity and personality traits of left- and right-handers during mental stress

The aim of the present study was to establish whether there is dependence of vascular reactivity to mental stress on the levels of neuroticism and anxiety in left- and right-handers. Thirty-two left-handed and 32 righthanded volunteers (16 males and 16 females in each group) between 18 and 30 years of age were studied. During mental stress both groups demonstrated a "standard" type of response, indicating an increase of the sympathetic-adrenal activity. In left-handers, however, the magnitude of the stress vascular reactivity was significantly higher (p<0.05) in comparison with that of right-handers. In left-handed females a moderate negative correlation between vascular reactivity and the levels of neuroticism (r = -0.39) and trait anxiety (r = -0.47, F = 4.04, p = 0.06) was established. In right-handed males a moderate positive correlation between neuroticism and vascular reactivity (r = 0.35) and significant positive correlation between trait anxiety and vascular reactivity (r = 0.60, F = 7.92, p = 0.01) was found. The results obtained show that vascular reactivity to mental stress is not influenced in a specific to left- and right-handers way by the levels of negative emotionality (neuroticism and trait anxiety).     

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.     

Motivation and motor control: hemispheric specialization for approach motivation reverses with handedness

Background

According to decades of research on affective motivation in the human brain, approach motivational states are supported primarily by the left hemisphere and avoidance states by the right hemisphere. The underlying cause of this specialization, however, has remained unknown. Here we conducted a first test of the Sword and Shield Hypothesis (SSH), according to which the hemispheric laterality of affective motivation depends on the laterality of motor control for the dominant hand (i.e., the “sword hand," used preferentially to perform approach actions) and the nondominant hand (i.e., the “shield hand," used preferentially to perform avoidance actions).

Methodology/Principal Findings

To determine whether the laterality of approach motivation varies with handedness, we measured alpha-band power (an inverse index of neural activity) in right- and left-handers during resting-state electroencephalography and analyzed hemispheric alpha-power asymmetries as a function of the participants'' trait approach motivational tendencies. Stronger approach motivation was associated with more left-hemisphere activity in right-handers, but with more right-hemisphere activity in left-handers.

Conclusions

The hemispheric correlates of approach motivation reversed between right- and left-handers, consistent with the way they typically use their dominant and nondominant hands to perform approach and avoidance actions. In both right- and left-handers, approach motivation was lateralized to the same hemisphere that controls the dominant hand. This covariation between neural systems for action and emotion provides initial support for the SSH.     

Memorization of sequences of right and left hand movements in right- and left-handers: Vector coding

Using studies of the right and left hemisphere’s specialization for positional and vector coding, we analyzed the errors made by right- and left-handers while reproducing sequences of right and left hand movements in a task that activates vector coding by changing the order of movements in memorized sequences. The task was performed first with one hand (starting) and then with the other (continuing). Both right- and lefthanders were found to use information about previous movements of the starting hand only when the dominant hand was starting. After changing the hand, right-handers used information about previous movements of the continuing hand, while left-handers did not. The results were compared with data from earlier experiments wherein positional coding was activated. The comparison showed that vector coding was predominantly involved in memorizing sequences of movements made by the dominant hand, while positional coding was used in the case of the opposite hand in both right- and left-handers. Patterns of errors after changing the hand differed between right- and left-handers, and the conclusion was made that skills are transferred in different ways in right- and left-handers, depending on the type of coding.     

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.     

Recovery of motor skills after the caudate lesion in rats with the different prefered forelimb: the role of intense retraining

Rats were trained for instrumental reaching (17 mm) of a sunflower seed from a horizontal tube 12 mm in diameter. After training, rats were divided into groups, "right-" and "left-handers", by the forelimb preference. Unilateral electrolytic lesions of the head of the caudate nucleus contralateral to the prefered forelimb were performed. After surgery, animals were retrained to perform the food-retrieval reaction by the same forelimb (reaching reaction by the "intact" forelimb was prohibited by a special bracelet). Both right- and left-handers were divided into groups of rare and intense retraining. Over the course of five months, animals of the groups of rare training were tested once a week, whereas the intense retraining was performed three or four times a week. Rats with right and left forelimb preference were shown to recover the reaching skill with different rates. In general, animals with left-side caudate lesion (right-handers) recovered the skill better both under condition of spontaneous recovery (rare testing) and intense retraining. The results suggest different mechanism of skill recovery after the right- and left-side brain lesion.     

Evaluation of hand asymmetry in relation to hand preference

We evaluated the asymmetric hand measurements in right- and left-handed individuals. 343 men and 290 women aged 18-42 years (22.11 +/- 2.07) participated in the study. There were no statistically significant differences when right-left differences in hand length, third finger length, palmar length, and the digit index value were evaluated according to hand preference and sex. Statistically significant differences were found for right-left differences in hand width, hand-shape index, and the palmar length/width according to hand preference. The strong left-handers, weak left-handers, and ambidextrous individuals in the study group all exhibited asymmetry favoring the left and were considered together. Similarly, the strong and weak right-handers exhibited asymmetry favoring the right hand and were considered together. The difference between these two groups was significant. When the data were evaluated according to sex, significant differences were found between the subgroups. In particular, right-left differences in the hand-shape index and palmar length/width values of the strong left-handers, weak left-handers, and ambidextrous individuals were found to be statistically significant according to sex; in contrast, the strong and weak right-handers showed no significant differences according to sex. These results suggest a relation of hand asymmetry to hand preference in a Turkish population.     

Dextrals and sinistrals (right-handers and left-handers): specificity of interhemispheric brain asymmetry and EEG coherence parameters

Data of literature about morphological, functional and biochemical specificity of the brain interhemispheric asymmetry of healthy right-handers and left-handers and about peculiarity of dynamics of cerebral pathology in patients with different individual asymmetry profiles are presented at the present article. Results of our investigation by using coherence parameters of electroencephalogram (EEG) in healthy right-handers and left-handers in state of rest, during functional tests and sleeping and in patients with different forms of the brain organic damage were analyzed too. EEG coherence analysis revealed the reciprocal changing of alpha-beta and theta-delta spectral bands in right-handers whilein left-handers synchronous changing of all EEG spectral bands were observed. Data about regional-frequent specificity of EEG coherence, peculiarity of EEG asymmetry in right-handers and left-handers, aslo about specificity of EEG spectral band genesis and point of view about a role of the brain regulator systems in forming of interhemispheric asymmetry in different functional states allowed to propose the conception about principle of interhermispheric brain asymmetry formation in left-handers and left-handers. Following this conception in dextrals elements of concurrent (summary-reciprocal) cooperation are predominant at the character of interhemispheric and cortical-subcortical interaction while in sinistrals a principle of concordance (supplementary) is preferable. These peculiarities the brain organization determine, from the first side, the quicker revovery of functions damaged after cranio-cerebral trauma in left-handers in comparison right-handers and from the other side - they determine the forming of the more expressed pathology in the remote terms after exposure the low dose of radiation.     

Female sexual swelling size, timing of ovulation, and male behavior in wild West African chimpanzees

Conspicuous swellings of the perineal skin can be observed in females of many catharrine primate species particularly during the middle stages of the ovarian cycle. The functional significance of this trait remains poorly understood. Recently, two hypotheses, the "reliable indicator" hypothesis and the "graded signal" hypothesis that take into account not only the pattern but also the exaggerated size of sexual swellings, have gained attention. Here we test several predictions made by these hypotheses by combining (i) direct size measures (from video captures) of female sexual swellings with (ii) urinary hormone data to indicate timing of ovulation through enzyme immunoassay measurements of estrone conjugates and pregnanediol glucuronide (PdG) and (iii) behavioral observations of male mating efforts throughout 36 ovulatory cycles in 12 wild chimpanzees. We are able to show that (i) even within the traditionally defined maximum swelling period, further slight increases in swelling size indicate approaching ovulation, and (ii) that male mating interest changes according to the changes in swelling size. Furthermore, absolute swelling size during the periovulatory period increases and the alpha male associates more with females as the number of cycles to conception decreases. Finally, when having the choice between several "maximally" tumescent females, the alpha male prefers the female that is in the fertile phase of her cycle rather than that with the biggest swelling at that time. Thus, most of our findings are in line with the predictions of the graded signal hypothesis while none of them would support the reliable indicator hypothesis.     

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.     

Linear Blood Velocity in Arteries of the Brain Hemispheres in Left-Handers and Right-Handers during Hypoxia

Transcranial Doppler ultrasonography was used to measure the linear blood velocity (LBV) in the middle cerebral artery (MCA) of the right and left hemispheres in right-handers and left-handers who were breathing a gas mixture with 10% oxygen through a mask at normal barometric pressure. No interhemispheric differences were found in left-handers before hypoxia. The maximum systolic velocity was higher in the MCA of the left hemisphere in right-handers. Left-handers had a higher LBV in the right hemisphere than did right-handers. LBV in the MCA of both hemispheres increased in both left-handers and right-handers as a result of hypoxia. Aggravation of hypoxia caused a decrease in LBV in the left hemisphere in right-handers.     

Handedness and the Vividness of Dreams

We provided a constructive replication of a recently published paper by measuring the relationship between handedness and recall of vivid dreams. To do this we asked groups of right- (N = 174), mixed- (N = 16) and left-handed (N = 13) university students to respond to a dream scale. Our data were consistent with those of the recent study in question in that we demonstrated that left-handers were significantly more likely to recall types of dreams that classified as a vivid. These data seem consistent with the profile of right hemispheric talent that is thought to characterize left-handers.     

Handedness frequency over more than ten thousand years

Although there are quite important geographical variations in the frequency of left-handers around the world, nothing is known about its temporal evolution. During the upper Palaeolithic (ca. 35,000-10,000 YBP), humans painted 'negative hands' by blowing pigments with a tube onto one hand applied on the rock in caves in Western Europe, by blowing pigments on their own hand through a tube held in the other hand. The frequency of left-handers prevailing during this period could thus be assessed. For comparison, the handedness of French university students has been observed for the same task. No difference was detected between the two proportions of left-handers, separated by more than 10,000 years. Implications for the evolution of the polymorphism of handedness are discussed.     

Effects of handedness on visual sensitivity in perihand space

Recent studies have shown that changes in visual processing in perihand space are limited to the area around the right hand, at least in right-handers. One explanation for these findings is that perception is altered at locations where action is more likely to occur. To test this notion, we asked both right- and left-handers to perform an unspeeded visual discrimination task under four hand-position configurations: Left hand, right hand, both hands, or no hands near the display. Compared to the no-hands (control) condition, visual sensitivity (d') was higher in the dominant-hand condition for right-handers and higher in the dominant- as well as the non-dominant hand condition for left-handers. When both hands were near the display, sensitivity was similar to that in the dominant-hand condition for right-handers and to that in the non-dominant hand condition for left-handers. This shows that performance differed between the two handedness groups when their non-dominant hand was near the display (both alone and accompanied by their dominant hand). Thus, the pattern for left-handers did not correspond to a mirror image of the pattern for right-handers. In line with studies on bimanual action control, visual processing in perihand space seems to be determined by the different ways in which left- and right-handers use their hands.     

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.     

Hypertension, and blood pressure response to graded exercise in young obese and non-athlethic Nigerian university students.

Hypertension, and the effect of graded exercise on Blood pressure (BP), in 60 obese non-athletic young medical students (40 females and 20 males) with Body Mass Index (BMI) greater than 30 were studied. The subjects were in the age range of 18-22 years with mean age of 20.30 +/-1.32 years. Twenty percent of the males and 7 percent of the females were found to be hypertensives [P < 0.05] and the severity of the hypertension significantly [P < 0.05] increased linearly with increase in BMI (r =0.6). Our study reveals a positive direct correlation between obesity and socioeconomic status and BP. Marked increases in systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial pressure (MAP), time of return (RT) were observed in the obese individuals compared to control at all levels of graded exercise with the highest rises seen during severe exercise. Among the obese subjects, the increases in BP were more in the males than females, but time of return was higher in females than males. This study further confirms that obese young individuals are prone to early onset of hypertension and thus other cardiovascular diseases and less tolerant to physical exercises. Our results add to the evidence that hypertension is common among obese young adults.     

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.     

Handedness is a determining factor in lateralized olfactory discrimination

The study aimed to re-investigate differences in olfactory thresholds and odor discrimination between the left and right sides in relation to the handedness of healthy subjects. Twenty left- and 20 right-handers participated; all were in excellent health with no indication of any major nasal or health problems, and all were non-smokers. The two groups were comparable in terms of sex and age (left-handers: 11 women, 9 men, median age 25 years; right-handers: 9 women, 11 men, median age 26 years). Odor thresholds did not differ in relation to handedness. However, in the odor discrimination task the left-handers performed significantly better at the left side compared with the right nostril; this pattern was reversed in the right-handers. The data indicate that, similar to other sensory systems, higher olfactory functions exhibit a certain degree of lateralization.