The distribution of hand preference in normal men and women

OCTA Signal Quality Augmentation Using the Isometric Handgrip Test to Maximize Vascular Flow (SQUEEZE): A Randomized Crossover Trial

Purpose

To determine if performing the isometric handgrip test (IHGT) can augment optical coherence tomography angiography (OCTA) vascular signal quality in eyes with macular abnormalities.

Methods

A randomized, single-blinded crossover trial was conducted including 36 participants with macular abnormalities, randomized to undergo OCTA with or without the IHGT, then crossed over to the alternate "intervention" after 1 minute. The primary outcome was OCTA signal quality after 1 minute of squeezing at 50% maximum grip strength. Secondary outcomes were other measures of vascular flow and systemic blood pressure (BP), also regressed against person- and eye-level covariables.

Results

Primary analysis of OCTA signal quality with versus without the IHGT was nonsignificant (P = 0.73). Nested analyses showed that the IHGT resulted in increased OCTA B-scan retinal vascular flow signal (2.95 [-1.64 to 7.55] Δ%, P < 0.05) and increased systolic BP, diastolic BP, pulse pressure, and mean arterial pressure (4.94 [0.41 to 9.47] to 12.38 [8.01 to 16.75] mm Hg, P < 0.05). OCTA signal quality and en face vessel density and perfusion changes were associated with sex, refraction, race/ethnicity, and right-hand IHGT use (P < 0.05). Greater increases in systolic and diastolic BP and mean arterial pressure were generally associated with right-hand IHGT use and greater maximum grip strength (P < 0.09).

Conclusions

The IHGT can temporarily increase OCTA B-scan retinal vascular flow signal in participants with macular abnormalities. IHGT-induced changes to systemic BP appear to be linked to absolute (rather than relative) grip strength, implying that the IHGT may be ineffective with low grip strength. Further research in larger populations is warranted.

Translational Relevance

This study provides early validation that the IHGT may augment OCTA output, which may lead to improved noninvasive detection of pathologic vascular changes.

Motor Proficiency, Manual Dexterity, and Visual Perception in School-age Children With ADHD: Contribution of Different Comorbidities

Attention-deficit/hyperactivity disorder (ADHD) is often comorbid with a number of other psychiatric conditions. The goal of this study was to investigate whether motor skills, manual dexterity, and visual perception differ in the presence of ADHD and comorbid psychiatric conditions in school-age boys by comparing them to a group of children with typical development (TD). We evaluated 81 boys 6 to 10 years of age in 5 groups: ADHD only (n=18); ADHD+specific learning disorders (ADHD+SLDs) (n=17); ADHD+oppositional defiant disorder (n=16); ADHD+anxiety disorders (n=15); and TD (n=15). The participants with ADHD only and those with ADHD+comorbidity had significantly lower scores than the participants in the TD group in every area we evaluated. The lowest scores were observed in the ADHD+SLD group in all motor skills domains except for the fine motor precision field. Furthermore, the group with ADHD+SLD had statistically significantly lower scores than the 3 other groups with ADHD+comorbidity in 3 areas: balance, upper extremity coordination, and speed and agility. Motor problems in patients with ADHD and comorbid conditions may not be a focus of attention in clinics. However, especially in the case of comorbid conditions accompanying ADHD, it is important to consider problems in motor skills, manual dexterity, and visual perception in evaluation and treatment to increase these children's quality of life.

Handedness related differences in the intracranial fluid spaces in healthy adults

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.

Similar effects of two different external supports on wrist joint position sense in healthy subjects: A randomized clinical trial

The hand is one of the most injured organs. Proprioceptive rehabilitation decreases the incidence of injury while using external supports can increase proprioception. The aim of this study was to investigate the effects of taping and elastic bandaging on wrist joint position sense (proprioception) in healthy individuals. Sixty-eight healthy students were included in our study and randomized into two groups. External supports were to apply to the dominant hand for 24hours in both groups. Joint position sense was evaluated with an angle reproduction test before applying the external support and 20 minutes after and then 24hours later with the external support and after removing it. There were significant improvements in joint position sense 20 minutes after applying the external support and 24hours later (P<0.05). Although a significant decrease in joint position sense was observed after removing the external support compared to while wearing it (P<0.05), there was a significant improvement in the joint position sense relative to the pre-study assessment (P<0.05). In between group comparisons, the only significant difference was observed 20 minutes after the external support was applied: the taping group had better results in joint flexion position sense than the bandaging group (P<0.05), but in the other assessments there were no significant differences between two groups (P>0.05). It was found that two different types of external support can improve the wrist joint's position sense in healthy subjects. These procedures can be used as a supplemental treatment in wrist rehabilitation.

Is the asymmetry between the vertebral arteries related to cerebral dominance?

Background/aim

The two vertebral arteries (VAs) are usually unequal in size; the left one is generally larger than the right one. It was hypothesized that the asymmetry results from the need of the dominant cerebral hemisphere for more glucose and oxygen, i.e. more blood supply. In this study, we aimed to test this hypothesis in patients by evaluating their arterial diameter and hand preference, as it is the most common criterion to determine the dominance of the hemisphere.

Materials and methods

The study was performed with 844 participants who consented to participate in the study. We identified the dominant cerebral hemisphere by asking participants about their hand preference. Then we measured both the VA diameter and VA flow volume by Doppler ultrasonography. After demonstrating the asymmetry, correlation was tested.

Results

Among 844 participants included in the study, the mean diameter of the right VA was 3.14 ± 0.35 mm and that of the left VA was 3.41 ± 0.54 mm, while the mean flow volume of the right VA was 119.21 ± 44.98 mL/min and that of the left VA was 151.45 ± 57.26 mL/min. It was recorded that 771 (86.43%) participants were right-handed and 73 (8.18%) were left-handed.

Conclusion

No significant relationship was found between the increased blood demand of the dominant cerebral hemisphere and the vertebral artery dominance.

Lateralization of Squamous Cell Carcinomas in the Head-Neck Region

Earlier studies have shown the lateralization of several immune disorders, including herpes zoster infection and breast cancer. We investigated whether there is lateralization of squamous cell carcinomas in the head-neck region and a relation of handedness with this cancer. Analysis showed right-sided lateralization of head-heck cancers in right-handed patients and vice versa in left-handed ones and a higher rate of left-handedness in patients with squamous cell cancer. Associations among left-handedness, squamous cell carcinoma, and its lateralization may result from a genetic togetherness.

Polyphasic Temporal Behavior of Finger-Tapping Performance: A Measure of Motor Skills and Fatigue

Successive voluntary motor movement involves a number of physiological mechanisms and may reflect motor skill development and neuromuscular fatigue. In this study, the temporal behavior of finger tapping was investigated in relation to motor skills and fatigue by using a long-term computer-based test. The finger-tapping performances of 29 healthy male volunteers were analyzed using linear and nonlinear regression models established for inter-tapping interval. The results suggest that finger-tapping performance exhibits a polyphasic nature, and has several characteristic time points, which may be directly related to muscle dynamics and energy consumption. In conclusion, we believe that future studies evaluating the polyphasic nature of the maximal voluntary movement will lead to the definition of objective scales that can be used in the follow up of some neuromuscular diseases, as well as, the determination of motor skills, individual ability, and peripheral fatigue through the use of a low cost, easy-to-use computer-based finger-tapping test.

Heart Rate Variability Differs between Right- and Left-Handed Individuals

Previous studies reported reduced longevity in left-handers with the suggestion that it may be associated with different heart diseases. Therefore, differences in heart rate variability (HRV), an index of autonomic cardiac activity, were examined for right- and left-handed individuals. 120 healthy young university students (75 women, 45 men; M age = 20.4 yr., SD = 1.5) volunteered. Handedness was assessed with the Edinburgh Handedness Inventory and HRV was measured via electrocardiography. The results suggest that the left-handers' HRV was significantly different from that of right-handers on several parameters. The atypical cerebral organization of left-handers may be related to an imbalanced autonomic system that results in higher frequencies of heart irregularities.

Turning bias in virtual spatial navigation: age-related differences and neuroanatomical correlates

Rodents frequently exhibit rotational bias associated with asymmetry in lesions and neurotransmitters in the striatum. However, in humans, turning preference is inconsistent across studies, and its neural correlates are unclear. We examined turning bias in 140 right-handed healthy adults (18-77 years old), who navigated a virtual Morris Water Maze. On magnetic resonance images, we measured volumes of brain regions relevant to spatial navigation. We classified turns that occurred during virtual navigation as veering (less than 10°), true turns (between 10° and 90°) and course reversals (over 90°). The results showed that performance (time of platform search and distance traveled) was negatively related to age. The distance traveled was positively associated with volume of the orbito-frontal cortex but not with the volumes of the cerebellum, the hippocampus or the primary visual cortex. Examination of turning behavior showed that all participants veered to the right. In turns and reversals, although on average there was no consistent direction preference, we observed significant individual biases. Virtual turning preference correlated with volumetric asymmetry in the striatum, cerebellum, and hippocampus but not in the prefrontal cortex. Participants preferred to turn toward the hemisphere with larger putamen, cerebellum and (in younger adults only) hippocampus. Advanced age was associated with greater rightward turning preference. Men showed greater leftward preference whereas women exhibited stronger rightward bias.

Lateralized α-motoneuron excitabilities during lying and standing of healthy individuals in relation to parkinsonian rigidity

OBJECTIVES

To elucidate mechanisms of Parkinsonian rigidity by assessing excitability of alpha-motoneurons innervating right and left soleus muscles in healthy controls and Parkinson's disease (PD) patients with rigidities in the right, left and both legs.

METHODS

One group of 45 controls was recruited and 60 PD patients in three groups: rigidities, predominantly in the right, left and both legs. H-reflex (H) and muscle response (M) were recorded from right and left soleus muscles during stimulations of the posterior tibial nerve at the popliteal fossa while lying and standing. The H/M ratio was taken as an index for motoneuron excitability.

RESULTS

Mean H/M ratios were significantly different on the right and left sides, modified by postural changes in controls and PD patients. Analysis of variance showed that in healthy subjects the H/M ratio was: standing>lying (right), lying>standing (left). In right leg rigidity patients, the H/M ratio was greatest during standing, and smallest during lying. In left leg rigidity patients, the H/M ratios on the right and left sides were equally independent of posture. In controls, left H/M>right while lying, <right while standing. In right leg rigidity patients, right H/M>left, but <right in left leg rigidity patients, independent of posture. There was no side difference in patients with rigidity in both legs.

CONCLUSIONS

(i) motoneuron excitability may show side and postural differences in healthy individuals and PD patients; (ii) posture may be associated with lateralized motoneuron excitability in these subjects; and (iii) Parkinsonian rigidity may have spinal motor origins.

The effect of right or left handedness on caries experience and oral hygiene

Background:

There is an indisputable relationship between tooth decay and oral hygiene. Caries can only be prevented by keeping tooth decay at bay. In several prophylactic methods, brushing is the most important. Brushing efficiency is directly related to an individuals' manual dexterity.

Objective:

To investigate whether there were differences in oral hygiene and caries prevalence between right- and left-handers.

Materials and Methods:

Forty-six elementary school students were included in the study. The subjects were 30 males and 16 females, ranging in age from 11 to 13 years. Handedness was ascertained by using the Edinburgh Handedness Scale. All students were examined intraorally. During this examination, the necessary values to determine oral hygiene status and to determine caries prevalence were recorded.

Results:

It was observed that subjects who used their right hands were in a better position in terms of oral hygiene than those using the left (P < 0.01). In terms of caries prevalence, however, averages for right-handed individuals were lower than those for left-handed subjects, although the difference was not statistically significant.

Conclusions:

It can be stated that the right-handed individuals have better oral hygiene and the lower incidence of caries because of their better manual dexterity and brush efficiency. So, dentists should consider better manual dexterity and brush efficiency in right-handed individuals before treatment planning. However, future well-designed neurologic studies involving larger numbers of subjects will be necessary to confirm the findings of this study and to understand more about the effects of handedness on oral hygiene performance.

Left-Handed Wrestlers are More Successful

It has been reported that there is a high proportion of left-handers among top athletes in different sports. In this study, the goal was to examine the rate of left-handedness in the top wrestlers at the world championships for achievement by left-handed wrestlers. The rate of left-handedness was higher in wrestlers with medal honors compared to wrestlers without medals for both men and women. The winning numbers and match degrees were higher in the left-handed wrestlers than in both right- and mixed-handed wrestlers among top international wrestlers.

Sex-related differences in tuberculin reaction, free and total testosterone concentrations in patients with autoimmune disorders and controls

Earlier studies reported the associations among testosterone hormone, autoimmunity, and left-handedness. In the present study, sex differences in tuberculin reaction, a measure of cell-mediated hypersensitivity, serum free and total testosterone levels in controls and patients with autoimmune diseases were studied. There was a sex difference in right and left tuberculin reactions in controls, but not in patients. Both right and left tuberculin reactions were smaller in male and female patients than male and female controls. Free and total testosterone levels were higher in male controls than in male patients. Total testosterone levels were higher in female controls than in female patients. These results suggest that autoimmune diseases may be associated with a decrease in the blood testosterone concentrations.

Differences by Sex and Handedness in Right and Left Femur Bone Mineral Densities

Left-handedness was reported to be a risk factor for accident-related injuries, head injuries, traumatic brain injuries, sport-related injuries, and bone breaks and fractures. As decreased bone mineral density is a good marker of bone fractures, the femoral bone mineral densities of normal left-handed university students were compared with those of right-handed students. Hand preference of 66 men and 47 women was assessed using the Edinburgh Handedness Inventory. Measures of bone mineral density with a Hologic QDR-4500W (S/N 48403) densitometer showed bone mineral densities of both right and left proximal femur regions were higher in right-handed than in left-handed students. These results are consistent with the claim that left-handed participants had higher trauma and injury risk. Also, these results may explain the sex-related differences by handedness for susceptibility in accident-related injuries such as bone fractures.

RELATIONSHIPS BETWEEN HAND AND FOOT PREFERENCES

The aim of this study was to evaluate the relations between hand and foot preferences in male and female individuals (343 male, 290 female) aged between 18-42 years (22.11 +/- 2.07). Of the right-handed men, 75.5% preferred the right foot, 7.1% the left foot, and 17.4% both feet. Of ambidextrous men, 44.0% preferred the right foot, 28.0% the left foot, and 28.0% both feet. Of left-handed men, 32.3% preferred the right foot, 56.9% the left foot, and 10.8% both feet. The differences between these percentages were found to be statistically significant. Of the right-handed women, 89.9% preferred the right foot, left foot 1.2%, both feet 8.9%, whereas 50.0% preferred the right foot, 12.5% the left foot, and 37.5% both feet in the ambidextrous women. In the left-handed women, 8.8% preferred the right foot, 79.4% the left foot, and 11.8% both feet. The differences between these percentages were found to be statistically significant. The results suggested that the cultural differences among the difference study groups may be the reason for the inconsistencies with regard to hand and foot preferences. Moreover, the results may bring insight into the foot preference in relation to hand preference in the Turkish population.

LONG-TERM EFFECTS OF MILD EXERCISE ON INTRAOCULAR PRESSURE IN ATHLETES AND SEDENTARY SUBJECTS

The long-term effects of acute submaximal exercise on intraocular pressures (IOPs) of right-and left-eyes and recovery times to basement levels of IOP in postexercise periods in sedentary and physically fit subjects were investigated. Twenty-five sedentary and 24 physically fit subjects, ranging in age 17 to 22 years, participated. Intraocular pressures were measured by a pneumotonometer. Measurements were taken in the morning at about nine (at rest) and immediately, 30 min and 2 h after acute submaximal exercise. In sedentary subjects, IOPs of both right- and left-eyes decreased immediate after exercise, but, these decreases in both eyes continued 30 min and 2 h after exercise. In physically fit subjects, IOPs of both right- and left-eyes increased immediate after exercise, but decreased after 30 min exercise compared to basement levels, and this decrease continued 2 h after exercise. Acute submaximal exercise decreased IOPs of right and left eyes over a period 2 h in sedentary and physically fit subjects. IOP reducing after exercise was different between right- and left-eyes in sedentary subjects. These results suggest that exercise can be used in ocular hypertension treatment.

MORPHOLOGICAL ASYMMETRY IN THYROID LOBES, AND SEX AND HANDEDNESS DIFFERENCES IN HEALTHY YOUNG SUBJECTS

The aim of the present study was to investigate sex and handedness differences in the sizes of the right and left thyroid lobes. Subjects were 72 healthy university students (36 female and 36 male), 18 to 23 years of age. Hand preference was assessed using the Edinburgh Handedness Inventory. The volumes of the right and left thyroid lobes were measured by ultrasonography. The right lobe was larger than the left. The right and left lobes were larger in men than in women. There were no handedness difference in the total thyroid volume and the volume of right lobe. But, the left lobe was larger in right-handed subjects than in the left handed ones. The difference (right minus left) was statistically larger in left-handers than in right-handers. The sex-related differences may be attributed to the sex differences in body weight. It can be stated that handedness is associated with the asymmetry of thyroid lobes.

Serum testosterone levels in male and female subjects with standard and anomalous dominance

Serum testosterone levels were determined in female and male subjects. Hand preference was assessed by the Edinburgh Handedness Inventory. Subjects with anomalous dominance (left-handers, mixed-handers, and right-handers with familial sinistrality) were compared to subjects with standard dominance (right-handers without familial sinistrality). The mean serum testosterone levels were found to be significantly higher in subjects with anomalous dominance than those with standard dominance. It was concluded that the results are in accord with the testosterone hypothesis of cerebral lateralization.

POPULATION-LEVEL RIGHT-PAW PREFERENCE IN RATS ASSESSED BY A NEW COMPUTERIZED FOOD-REACHING TEST

We re-studied the distribution of paw preference in rats using a new computerized food-reaching test, which recorded the times and time intervals between the single right- and left-paw entries. Using the traditional food-reaching test, we found that of 144 rats, 72.7% were right-handed, 19.7% left-handed, and 7.6% mixed-handed. This population-level J-shaped right-hand preference did not fit a binomial chance distribution (25:25:50). Of right -handers, 99.5% first used their right paw and 0.5% left paw; of left-handers, 98.6% first used their left paw and 1.4% right paw. Of mixed-handers, 59% first used the right paw and 41% left paw for food reaching. The time interval between putting the rat into the test cage and the first right-paw entry was significantly shorter than the first left-paw entry in total sample. Males were faster than females (shorter time intervals between right- or left-paw entries). The distribution of the time intervals between right- or left-paw entries was inverse J-shaped, which exhibited a normal distribution after taking the logarithms of the time intervals. There was no significant difference between time intervals for the left-paw entries; time intervals for the right-paw entries were significantly shorter in males than females, accentuating the role of the left brain for sex differences in motor control. The results suggested that humans are not unique in population-level right-hand preference; our new method would be suitable for new developments in handedness research.

HAND PREFERENCE IN TURKISH POPULATION

The distribution of hand preference (self report) was studied in siblings and their parents originating from all parts of Turkey (N = 22,461). In total sample and siblings, there were significantly more right-handed women than men, and significantly more left-handed men than women--no significant sex difference for parents' handedness. The relative number for the right-handed parents significantly exceeded that for the right-handed siblings; the relative number for the left-handed siblings significantly exceeded that for the left-handed parents. It was concluded that there may be a sex difference in hand preference, but being only about 1% more left-handed men, and only about 1% more right-handed women; the right-handedness in new generation (siblings) is less than that in old generation (parents), due to freeing from cultural pressures against the left-hand use in everyday activities.

EFFECT OF ACUTE SUBMAXIMAL EXERCISE ON INTRAOCULAR PRESSURE IN ATHLETES AND SEDENTARY SUBJECTS

The existing literature is controversial regarding the relationship between physical fitness and intraocular pressure (IOP). Therefore, the effects of acute submaximal exercise on IOP were compared in athletes and sedentary subjects. Acute exercise increased IOP in male athletes, but had no effect in sedentary men. Also, it decreased IOP in sedentary women, but had no effect in female athletes. Sex and physical fitness both were significant factors influencing the changes in IOP due to exercise. These results suggest that acute dynamic exercise is useful to decrease IOP in sedentary women, but not in male athletes. These results may help glaucoma screeners.

The relationships between nonverbal intelligence and the strength of left-hand preference in left-handers to sex and familial sinistrality

The relationship between the strength of left-handedness and spatial reasoning ability was studied in left-handed male and female subjects with and without familial sinistrality (FS). The degree of left-handedness was assessed by the Edinburgh Handedness Inventory. The spatial reasoning ability was measured by Cattell's Culture Fair Intelligence Test. It was found that there was a negative linear correlation between nonverbal IQ and the strength of left-handedness in females with and without FS, a quadratic relationship in male left-handers without FS and a positive linear correlation in male left-handers with FS. These results indicate that the brain may exhibit different patterns of cerebral organization in left-handers to sex and FS. It was concluded that the "crowding" hypothesis may apply only to a subgroup of left-handers, i.e., females with a greater bilaterality of cognitive functions than males.

Lateralizations of head-neck cancers are not associated with peripheral asymmetry of cell-mediated immunity

Earlier studies have reported right-sided lateralization for different organ cancers except breast cancer. In the present study, lateralization of head-neck cancers and their relation with the peripheral cell-mediated immune asymmetry was investigated. The sample was comprised of 42 men and 20 women diagnosed with cancer in the head-neck region. The diagnosis of cancer was made histopathologically. To measure the cell-mediated (type IV) immunity of both forearms, the tuberculin test (PPD test) was used in the subjects previously sensitized by BCG vaccine during the first year of age. Significant right-sided lateralization in men and the significant left-sided lateralization in women were observed in this study. There was no relation between the lateralization of cancer and the asymmetry of tuberculin reaction or the peripheral cell-mediated immune asymmetry.

Left-handedness in blind and sighted children

Rates of left-handedness were compared in 1387 blind and 831 sighted children. The rate in male blind children was higher than in female blind children. The incidence of left-handedness was significantly higher in blind than in sighted children in both boys and girls. The percentages of left-handedness were 18.23% and 17.02% in male and female blind children, and 11.02% and 7.52% in male and female sighted children, respectively. It can be stated that sighting is important in the development of normal typical cerebral lateralisation or hand preference.

Dynamics of manual skill: a computerized analysis of single peg movements and stochastic resonance hypothesis of cerebral laterality

Hand skill was analyzed using a computerized peg moving task. The durations of single hand movements (PMTs) were accurately measured in right-hand (RH) and left-hand (LH) writers. One trial consisted of 10 movements of the right hand and 10 movements of the left hand. Each participant performed five trials. Women showed significantly higher percentage than men in right-handedness; men showed higher percentage than women in left-handedness. This sex difference completely disappeared after taking the same height range in participants. The mean RH- and LH-PMTs decreased in 5 successive trials, even within a single trial during 10 successive hand movements, indicating a learning effect of repeated hand movements. The LH- minus RH-PMTs exhibited fluctuations within a single trial between positive (faster right hand) and negative (faster left hand) values. LH-RH PMTs were significantly greater than zero, in favor of right hand, in RH-writers, but not significantly different from zero in LH-writers, exhibiting a true fluctuating asymmetry. Participants with no familial sinistrality (FS-) were preponderantly right-handed (ca. 90%), those with left-handed mother and right-handed father (FS+1) showed stochastic distribution of hand preference (50:50). Participants with right-handed mother and left-hander father (FS+2) were not different from FS- individuals. LH-RH PMT was significantly greater than zero in FS- participants, almost equal to zero in FS+1 participants, and greater than zero in FS+2 participants exhibiting greater asymmetry than that in FS- participants. These results suggest a genetic inheritance of direction and degree of handedness, being a a X-linked trait originating from mother's genotype. It was suggested that fluctuating asymmetries may reflect interactions between stochastic resonance phenomena within right and left brains. This property of brain may genetically transmitted from mother's X chromosome; a net effect of stochastic interactions between hemispheres may result in right- or left-handedness, a predominantly unidirectional coupling creating right-handedness, in favor of left brain, and a stochastic bi-directional coupling between hemispheres would be a main trait of left-handers. This new "stochastic resonance hypothesis of cerebral laterality" concerns with stochastic fluctuations in hand-skill asymmetry and inter-hemispheric coupling through corpus callosum, and seems to be important for new developments in handedness research.

Clinical importance of asymmetry and handedness differences in common carotid artery intima-media thickness

Earlier publications have reported that common carotid artery intima-media thickness (CCA-IMT) was lower on the right side than on the left side and that left-handed patients have a lower risk of sudden death of brain infarction. This study aimed to determine whether there is an asymmetry and the handedness related difference in CCA-IMT. Ultrasonographic examinations were performed with the use of Aplio US system. In total sample, male and female left-handers, CCA-IMT was greater on left side than on right side. In men, both right and left CCA-IMTs, but in women only right IMT, were lower in the left-handers than in the right-handers. Both right and left CCA-IMTs was positively correlated with age in men and in women. Handedness was a significant factor influencing CCA-IMT with adjustment for sex and age. It was greater on left side than on right side, especially in the left-handers. CCA-IMTs were lower in the left-handers than in the right-handers. These results suggest that hemodynamic stress and intimal damage was larger in the left carotid artery, which was larger in the right-handers compared to the left-handers.

The formation of cataract is earlier in the dominant eye

Relations among handedness, eye dominance, and lateralisation in the formation of cataract were investigated in 35 male and 21 female patients with cataract. In right-handed patients, cataracts formed earlier in the right eyes than in the left eye; this was reversed in left-handed patients. For both right- and left-eye dominant patients, cataracts formed earlier in the dominant eye.

A high-precision, low cost system for evaluating finger-tapping tasks

Finger-tapping test is extensively employed to assess motor asymmetry in brain damaged patients and also to study the relationship between handedness and performance in normal subjects. The aim of this study was to develop a computer based finger-tapping system that could provide quantitative measures of finger-tapping performance. The system is designed to be used in a standard personnel computer without the need of any other hardware. The software is written in Borland Delphi 6.0 for Microsoft Windows 98 and higher operating systems. Beginning with the Pentium processor, it could be possible to access a time-stamp counter. The time-stamp counter is a 64-bit machine specific register that is incremented by every clock cycle, and keeps an accurate count of every cycle that occurs on the processor. By using a computer with 1 GHz processor speed it is possible to reach a high precision time resolution of 1 mus in finger-tapping tests. Our future prospects for the system are to improve it with various tools such as synchronized recording of electromyography, tapping force monitoring, monitoring of finger angle, and the response to different stimulus parameters by adding appropriate hardware and procedure.

Asymmetry of the height of the ethmoid roof in relationship to handedness

The aim of this work was to study the handedness differences in the height of the right and left ethmoid roofs. Hand preference was assessed using the Edinburgh Handedness Inventory. The height of the right and left ethmoid roofs was measured with computerised tomography (CT). The incidence of persons who had a lower ethmoid roof on the right side was significantly greater among right-handers than among left-handers; the incidence of persons who had a lower ethmoid roof on the left side was significantly greater among left-handers than among right-handers; and right and left ethmoid roofs were equal in all ambidextrous subjects. The relationship between the asymmetric ethmoid roofs and handedness may result from the right or left embryonic craniofacial region being smaller in the right- or left-handed subjects. This is particularly important in the light of the high degree of variability in the ethmoid roof, and even between the right and left sides in a given individual. Preoperative awareness of a patient's unique sinus anatomy may help prevent iatrogenic injury to the surrounding vital structures during ethmoid sinus surgery (ESS).

Sex and eyedness in a sample of Turkish high school students

The relationship of sex with eyedness was examined in 176 boys and 129 girls ages 15 to 21 years (M = 16.9 yr., SD = 1.8) in Turkish high schools. Sex was significantly associated with handedness; the rate of left-handedness was 10.8% in boys and 2.3% in girls and was not related to eyedness. Rate of left-eyedness in the sample was 7.9% for boys and 8.5% for girls. One may wonder whether eyedness shows a reverse sex effect, less than handedness, but methods of measurement must be compared.

Handedness, eyedness, and crossed hand-eye dominance in male and female patients with migraine with and without aura: a pilot study

The possible relationships of migraine to left-handedness and left-eyedness, as well as sex and aura-related differences, were examined. 146 migraine patients (M age=32.1 yr., SD=9.5) and 141 controls (M age=30.0 yr., SD=9.3) participated. Hand preference was assessed by the modified version of the Edinburgh Handedness Inventory. Ocular dominance was measured by means of the near-far alignment test. Migraine diagnoses were made on the basis of criteria provided from the International Headache Society. In the overall sample and in women, left-handedness and left-eyedness were not significantly correlated with migraine. In men, the incidence of left-handedness and left-eyedness were significantly higher in patients than in controls. The presence of aura in patients with migraine was significantly associated with the incidence of left-eyedness and crossed hand-eye dominance, but not handedness, for the total sample and women. These results suggest that there may be a tendency towards anomalous dominance, especially left-eyedness, in migraine patients particularly those with aura.

Effect of handedness on learning subgingival scaling with curettes: a study on manikins

The aim of the present study was to evaluate the influence of systematic manikin-head training and the effectiveness of subgingival scaling applied with hand instruments (curettes) by right- and left-handed dental students on dental chairs (traditional) designed for right-handers. A questionnaire focusing on handedness was administered to 69 voluntary dental students in the third class at the School of Dentistry during pre-participation examination. Handedness was assessed using the Turkish version of the Edinburgh Handedness Inventory. Then, 18 dental students were specially selected in 2 equal groups according to hand preference: consistent right-handers with Geschwind Scores of +100 (5 female and 4 male) and consistent left-handers with Geschwind Scores of -100 (5 female and 4 male). These two untrained dental student groups received 10 weeks manikin-head training. Subgingival scaling was performed with hand instruments (Gracey curettes) in manikin-head mounted on right-sided dental chairs. At 6 test days each dental student had to instrument 12 test teeth. Effectiveness of subgingival scaling was evaluated by adoption of a grading system. This system had scores from 0 to 3 and was defined by illustrated and described criteria. Statistical analysis was carried out with SPSS. Two groups were statistically compared on all test days. The yet-untrained left-handed dental students begin with a relatively high the mean score of 2.25, compared to the yet-trained right-handed dental students with 1.93, which was statistically significant (p > .05). The right-handed dental students reached the mean score of 0.53, whereas the left-handed dental students reached the mean score of 0.87 on test day 6. Significant differences in the mean scores were found between the two groups for overall surfaces (p < .05), the distal surfaces (p < .01), lingual surfaces (p < .01), and each group of teeth (p < .05). But there was no statistically significant difference between the 2 groups of students on all test day, except for test day 3 in terms of the mean scores for the facial and mesial surfaces (p > .05). Learning success was observed a high level in both groups through systematical training (p < .0001). The present study has documented that the left-handed dental students were less successful than the right-handed dental students in subgingival scaling, except for mesial and facial surfaces. However although training on right-sided chairs, they were quite similar to their right-handed counterparts in terms of learning success.

Correlations among handedness, eyedness, monocular shifts from binocular focal point, and nonverbal intelligence in university mathematics students

Relationships among hand preference, nonverbal intelligence, and the monocular shifts of binocular focal point were studied in 33 men and 12 women university mathematics students. Ocular dominance was assessed with the Miles test. The monocular shift of binocular focal point for each eye was assessed with a modified Miles test. Hand preference was assessed on the Edinburg Handedness Inventory. Nonverbal intelligence was assessed with Cattell's Culture Fair Intelligence Test. In a prior study, the percentage of left-eye preference had been reported to be greater for mathematics students than for nonmathematics students. In the present study there were positive correlations between hand preference and the sum of the monocular shifts of two eyes. In addition, there was a negative correlation between nonverbal intelligence and the sum of the monocular shifts of two eyes. As these resultssuggest that the sum of the monocular shifts of two eyes may be related to mathematical ability and nonverbal intelligence, further research with a larger sample including non-mathematics students is needed.

CORRELATIONS BETWEEN NONVERBAL INTELLIGENCE AND NERVE CONDUCTION VELOCITIES IN RIGHT-HANDED MALE AND FEMALE SUBJECTS

A neurological theory of intelligence suggesting a direct correlation between nerve conduction velocity and psychometric intelligence was tested. Cattell's Culture Fair Intelligence Test was used to asses the nonverbal intelligence (IQ) of subjects. The motor median nerve conduction velocity from right hand of males was positively correlated with IQ. In subjects with no familial sinistrality (FS-), the motor ulnar-nerve conduction velocity from the right and left hands of males negatively correlated with IQ; there were inverse correlations between IQ and nerve conduction velocity (motor median nerve from right, sensory median nerve from right and left) in females. In subjects with familial sinistrality (FS+), IQ directly correlated with nerve conduction velocity from motor median (right and left), sensory median (right), and motor ulnar (right) nerves, but only in males. The speed hypothesis and neurological theory of intelligence were not supported by these results, which, in contrast, emphasized the importance of sex and familial sinistrality in any theory of intelligence.

Handedness differences in widths of right and left craniofacial regions in healthy young adults

In this work, handedness differences in the widths of right and left craniofacial regions were studied in a healthy sample of 39 male and 43 female students, 17 to 23 years old. Width of craniofacial regions was assessed by computerized tomography. Handedness was associated with the left face width especially for women. The left facial region was larger for right-handers than left-handers. The smaller measure for the left face of left-handers might be associated with an advantage of left ear sensitivity.

Sport injuries: relations to sex, sport, injured body region

The present study evaluated the association among sex, sport, and injured body region of sport injuries. The subjects were 329 men and 127 women, ranging in age from 17 to 28 years, attending classes in the departments of Physical Training and Sport of Atatürk University (Erzurum, Erzincan, and Ağri in Turkey). There were no differences between men and women in percentages of injuries. The difference among various sports in the percentages of injured athletes was statistically significant. Running had the lowest percentage of injuries and basketball had the highest percentage. The most frequently injured body regions were the foot and the ankle in basketball, volleyball, soccer, and running, but in wrestling, the knee. These findings suggest that injury rates are associated with the sport rather than sex of player, and the most frequently injured body regions are the lower extremities. Therefore, the muscles of lower extremity should be strengthened to avoid injuries.

Sex and handedness differences in size of cerebral ventricles of normal subjects

Sex and handedness differences in the volumes of cerebral ventricles were studied in 20 right- and 21 left-handed subjects. To assess the volumes of cerebral ventricles, Cavalieri's method was used using MRI. In right-handers, the volume of the lateral ventricle was higher in the right side than in the left side, but, in left-handers, it was higher in the left side than in the right side. The volumes of right-lateral and third ventricles were larger in right-handers than in left -handers. There were no sex related differences in terms of the volumes of right- and left -lateral, third, and fourth ventricles. These results suggest that left-handedness is an important factor reducing the sizes of all the brain ventricles.

Sex-related difference in intraocular pressure in healthy young subjects

Sex-related differences in intraocular pressures of the right and left eye was studied in 64 men and 61 women, all young and right-handed. Intraocular pressures of the right and left eye were higher for women than men. Sex-related difference in intraocular pressure may be associated with presence of the sex hormone, oestrogen, in women which reduces sympathetic activity.