Left-handed Group Research Articles

Asymmetry of the Frontal Aslant Tract Depends on Handedness.

The human brain displays structural and functional disparities between its hemispheres, with such asymmetry extending to the frontal aslant tract. This plays a role in a variety of cognitive functions, including speech production, language processing, and executive functions. However, the factors influencing the laterality of the frontal aslant tract remain incompletely understood. Handedness is hypothesized to impact frontal aslant tract laterality, given its involvement in both language and motor control. In this study, we aimed to investigate the relationship between handedness and frontal aslant tract lateralization, providing insight into this aspect of brain organization. The Automated Tractography Pipeline was used to generate the frontal aslant tract for both right and left hemispheres in a cohort of 720 subjects sourced from the publicly available Human Connectome Project in Aging database. Subsequently, macrostructural and microstructural parameters of the right and left frontal aslant tract were extracted for each individual in the study population. The Edinburgh Handedness Inventory scores were used for the classification of handedness, and a comparative analysis across various handedness groups was performed. An age-related decline in both macrostructural parameters and microstructural integrity was noted within the studied population. The frontal aslant tract demonstrated a greater volume and larger diameter in male subjects compared with female participants. Additionally, a left-side laterality of the frontal aslant tract was observed within the general population. In the right-handed group, the volume (P < .001), length (P < .001), and diameter (P = .004) of the left frontal aslant tract were found to be higher than those of the right frontal aslant tract. Conversely, in the left-handed group, the volume (P = .040) and diameter (P = .032) of the left frontal aslant tract were lower than those of the right frontal aslant tract. Furthermore, in the right-handed group, the volume and diameter of the frontal aslant tract showed left-sided lateralization, while in the left-handed group, a right-sided lateralization was evident. The laterality of the frontal aslant tract appears to differ with handedness. This finding highlights the complex interaction between brain lateralization and handedness, emphasizing the importance of considering handedness as a factor in evaluating brain structure and function.

The relationship between immunological and psychopathological characteristics in patients with focal epilepsy depending on the profile of interhemispheric asymmetry

To identify the possible influence of cellular immunity parameters and neurobiological variables (frequency of seizures of various semiotics and their severity) on comorbid psychopathological symptoms depending on the profile of interhemispheric asymmetry in patients with focal forms of epilepsy. The study included 92 patients with epilepsy (38 men, 54 women, mean age 38.7+8.45 years). Focal temporal lobe epilepsy was diagnosed in 36 patients, focal frontal lobe epilepsy in 16 patients, and temporal-frontal lobe epilepsy in 40 patients. For each type of seizure, severity was assessed according to the National Seizure Severity Scale (NHS3). The mental status of patients was assessed using the SCL-90 self-report questionnaire. The Annette scale was used to assess the profile of interhemispheric asymmetry. The number of different clusters of lymphocytes was studied, including the number of T-lymphocytes (CD3+), T-helpers (CD3+CD4+), T-cytotoxic (CD3+CD8+), T-NK (natural killers CD3+CD16+CD56+), B-lymphocytes (CD3-CD19+), as well as immunoregulatory index (CD4/CD8 ratio). In order to identify any possible relationships between neurobiological and immune variables, on the one hand, and the SCL-90 constructs, on the other hand, a separate correlation analysis of Spearman ranks within the left-handed group and the right-handed group was carried out. We revealed the differences between groups of patients with epilepsy with right and left profiles of hemispheric asymmetry regarding the relationship between the frequency of seizures, their severity and accompanying psychopathological variables, on the one hand, and between immunity indices and psychopathological constructs, on the other hand. It has been established that neurobiological and immune variables in left-handers can determine the psychopathological structure of the comorbid mental disorder. Prediction of concomitant psychopathological syndromes in patients with epilepsy on the basis of clinical data and data on immunity is quite possible, but only in left-handed patients.

Effects of handedness on brain oscillatory activity during imagery and execution of upper limb movements.

Brain activation during left- and right-hand motor imagery is a popular feature used for brain-computer interfaces. However, most studies so far have only considered right-handed participants in their experiments. This study aimed to investigate how handedness influences brain activation during the processes of imagining and executing simple hand movements. EEG signals were recorded using 32 channels while participants repeatedly squeezed or imagined squeezing a ball using their left, right, or both hands. The data of 14 left-handed and 14 right-handed persons were analyzed with a focus on event-related desynchronization/synchronization patterns (ERD/S). Both handedness groups showed activation over sensorimotor areas; however, the right-handed group tended to display more bilateral patterns than the left-handed group, which is in contrast to earlier research results. Furthermore, a stronger activation during motor imagery than during motor execution could be found in both groups.

Generalization of Spin Operators

The study shall look to the group of generators SU(4). From these generators, a new group spin operator will be constructed. We will classify these groups into right handed groups and left handed groups. These two groups will satisfy all the properties of Pauli spin operators Sx, Sy and Sz with respect to the frame xyz. The analysis shows that the number of groups spin operators depends on the order of the group. This leads us to construct the theorem which defines the number of the groups spin operators. The analysis also leads to two kinds of frames: left handed frame (LHF) and right handed frame (RHF). The right handed operators will act on the RHF, and left hand operators act on the LHF. The study shall discuss the notion of spin squeezing for pure spin 3/2 system by using our new frames and new spin operators. It will show that our calculation is equivalent to the calculation by using Pauli spin operators.

Left-Handers Are Less Lateralized Than Right-Handers for Both Left and Right Hemispheric Functions.

Many neuroscientific techniques have revealed that more left- than right-handers will have unusual cerebral asymmetries for language. After the original emphasis on frequency in the aphasia and epilepsy literatures, most neuropsychology, and neuroimaging efforts rely on estimates of central tendency to compare these two handedness groups on any given measure of asymmetry. The inevitable reduction in mean lateralization in the left-handed group is often postulated as being due to reversed asymmetry in a small subset of them, but it could also be due to a reduced asymmetry in many of the left-handers. These two possibilities have hugely different theoretical interpretations. Using functional magnetic resonance imaging localizer paradigms, we matched left- and right-handers for hemispheric dominance across four functions (verbal fluency, face perception, body perception, and scene perception). We then compared the degree of dominance between the two handedness groups for each of these four measures, conducting t-tests on the mean laterality indices. The results demonstrate that left-handers with typical cerebral asymmetries are less lateralized for language, faces, and bodies than their right-handed counterparts. These results are difficult to reconcile with current theories of language asymmetry or of handedness.

Examination and Comparison of Theta Band Connectivity in Left- and Right-Hand Dominant Individuals throughout a Motor Skill Acquisition

The majority of the population identifies as right-hand dominant, with a minority 10.6% identifying as left-hand dominant. Social factors may partially skew the distribution, but it remains that left-hand dominant individuals make up approximately 40 million people in the United States alone and yet, remain underrepresented in the motor control literature. Recent research has revealed behavioral and neurological differences between populations, therein overturning assumptions of a simple hemispheric flip in motor-related activations. The present work showed differentially adaptable motor programs between populations and found fundamental differences in methods of skill acquisition highlighting underlying neural strategies unique to each population. Difference maps and descriptive metrics of coherent activation patterns showed differences in how theta oscillations were utilized. The right-hand group relied on occipital parietal lobe connectivity for visual information integration necessary to inform the motor task, while the left-hand group relied on a more frontal lobe localized cognitive based approach. The findings provide insight into potential alternative methods of information integration and emphasize the importance for inclusion of the left-hand dominant population in the growing conceptualization of the brain promoting the generation of a more complete, stable, and accurate understanding of our complex biology.

Advantages of the Left-handed Ultrasonic Shears Technique for Robotic Gastrectomy.

The aim of this study was to investigate advantages of the left-handed ultrasonic shears technique in robotic gastrectomy for gastric cancer. We retrospectively analyzed 67 consecutive gastric cancer patients who underwent robotic gastrectomy. Fifty-six patients underwent gastrectomy with the left-handed ultrasonic shears technique (the left hand group), and 11 patients underwent surgery with the conventional approach (the conventional group). Intraoperative and postoperative outcomes were compared between the 2 groups. Operative blood loss, morbidity, and mortality were similar between the 2 groups. We observed a trend toward a shorter operation time and higher number of retrieved lymph nodes in the left hand group compared with the conventional group. Console time (docking-gastrectomy) in the left hand group was significantly shorter than in the conventional group (192.20 vs. 218.36 min, P<0.05). In robotic distal gastrectomy, both operation time and console time in the left hand group were significantly shorter than in the conventional group (276.10 vs. 354.80 min, 176.43 vs. 209.20 min, P<0.05 for both). The postoperative intra-abdominal infectious complication (Clavien Dindo≥1) rate in the left hand group was significantly lower than that in the conventional group (0% vs. 20%, P<0.05). Use of the left-handed ultrasonic shears technique is safe and provides a technically superior operative environment with satisfactory postoperative results.

Gender differences in functional connectivity of left-handers during the passage of an emotional stroop task

ntroduction. Neural correlates underlying the processing of emotional information, influence of emotional interference on cognitive control, gender difference in such activities remain a topic of research and discussion.Purpose. To study the connectivity of the brain regions involved in the processing of emotional information in left-handers, based on the EEG data obtained during their passage the emotional Stroop test (EST).Methods. EEG was registered during subjectpassage the EST successively two times. In EST a series including 240 words were presented at the center of the computer screen in one of two colors: red or green, words were emotional (negative) or neutral, shown in pseudorandom order. Some of these stimuli (target words names of animals and plants) participants were instructed to ignore (do not press any keys). Subjects were asked to respond with right hand (pressing P on a keyboard) for words printed in red and with left hand (pressing Q on a keyboard) for words printed in green. It was investigated source level functional connectivity (FC) in two groups of left-handers (17 to 22 years old): women (n=10) and men (n=10). FC was analysed between 21 regions of interest (ROI), selected on the base of fMRI research literature. Connections between ROIs were assessed using lagged phase synchronization (LPS) with eLORETA complex.Results. Statistically significant differences in FC by LPS between men and women groups were found only in first passage of EST. Particularly, FCof women, compared to men was: -higher between anterior cingulate cortex and left middle temporal area in delta band;-lower between left hippocampal formation and right frontal eye fields in beta-1;-and higher in beta-2 between right frontal eye fields and right anterior insula.were shorter for both emotional and neutral words. The interference effect was observed in both tests in women and only in the first test in men. Interference effect also was higher for responses with left hand for both groups. Repeated passage of the emotional Stroop test leads to reducing the effect of interference in men but not in women.Originality.The main neural networks have been identified, which in left-handed women are more involved in the processing of negative emotional information than in left-handed men.Conclusion. Compared to men, women have stronger connections of two areas of the brain involved in processing negatively colored emotional information, with other areas of the brain. The anterior cingulate cortex, which is considered to playan important role in attention and executive functions, is connected to the left middle temporal area, involved in the analysis of visual movement and words processing. Activation of theright anterior insular cortex, which is closely related to emotionalprocessing, is connected to the right frontal eye fields, which are known to play a key role in the goal directed eyes movements.Contrary, area of right frontal eye fields of men is more tightly connected to the contralateral left hippocampus, and is involved in semantic rather than emotional processing of information.Key words: emotional Stroop test;gender differences; left-handers; EEG; functional connectivity

Functional MRI study of language organization in left-handed and right-handed trilingual subjects

Functional MRI (fMRI) is gaining importance in the preoperative assessment of language. Selecting the appropriate language to test by fMRI in trilingual patients is intricate. Our objective is to compare fMRI maps for all three languages in left- and right-handed trilingual subjects. 15 right- and 15 left-handed trilingual volunteers were included in the study. We performed fMRI for each volunteer with a visual responsive naming paradigm that was repeated three times, once in each language. The activated areas and the laterality indices were calculated and correlation with the age of acquisition and proficiency of each language was determined. Strong statistical correlation was found between the Laterality Index (LI) of the three languages, in both the right and left-handed groups. Discordant lateralization of language was only observed in four left-handed subjects who demonstrated bilateral and left-lateralization. In right-handed subjects, the activation maps for the first and the second acquired language were similar. The largest activation was seen with the last acquired language. Irrespective of language proficiency and age of acquisition, the language lateralization might change for left-handed subjects. In right-handed subjects, there is no change and the last acquired language results in the largest activation. fMRI performed for a single language can accurately determine language lateralization in right-handed subjects, whereas in left-handed subjects, it is mandatory to test all languages.

Investigation of Functional Connectivity During Working Memory Task and Hemispheric Lateralization in Left- and Right- Handers Measured by fNIRS

Working memory is regarded as a cognitive system with limited capacity, which is responsible for saving, manipulating, and remembering online information. The cognitive functions of the brain, such as language, understanding, planning, reasoning, and problem-solving, need working memory. Based on the previous studies, working memory is considered as a central function of frontal brain lobe. Among several protocols on assessing working memory function, the n-back task is regarded as one of the most common ones in the functional imaging studies of working memory. Functional near-infrared spectroscopy (fNIRS) is an optical imaging method for evaluating brain function, which measures nervous activities and hemodynamic response in the cerebral cortex. The present study aimed to assess functional connectivity in frontal brain lobe during conducting dual n-back task at three levels of memory loading (n = 0, 1, 2) by using fNIRS signals. The statistical population included 29 healthy volunteers, among which 11 and 18 ones were left- and right-handed, respectively. They performed a dual n-back task, and the change in the concentrations of Hb and HbO2 was measured by using 24 fNIRS channels existing in the frontal lobe. The matrix of functional connectivity was extracted and evaluated by using partial correlation criterion for all participants and each of right- and left-handed groups at every level of memory loading separately. The statistical analyses of Hb and HbO2 signals (p < 0.05) in each group represented the presence of a bilateral connection between two hemispheres and local connection ones between different areas in each hemisphere with more connectivity in the right hemisphere of the frontal cerebral cortex during conducting the dual n-back task. Based on the comparison of the results related to left- and right-handed groups, a difference was observed between their functional connectivity in some areas, as well as the number of connectivity between various areas. Right-handed participants more utilized the lateralization of the right hemisphere to perform task compared to left-handed did, while left-handed ones represented the decrease in lateralizing or distributing bilaterally in hemispheres, by indicating the difference between some of the brain connectivity were different in these participants by considering the dominance of one of the hemispheres in each of these two groups. In general, the results of the present study demonstrated that fNIRS data is considered as appropriate for assessing the functional connectivity between the different areas of the frontal cerebral cortex during conducting the working memory-related tasks.

Shifts of the point-of-change can be attributed to a lower mechanical cost of motor execution

In a previous study on hand selection in a sequential reaching task, the authors showed a shift of the point-of-change (POC) to the left of the midline. This implies that participants conducted a number of contralateral reaches with their dominant, right hand. Contralateral movements have longer planning and execution times and a lower precision. In the current study, we asked whether lower mechanical costs of motor execution or lower cognitive costs of motor planning compensated for these disadvantages. Theories on hemispheric differences postulate lower mechanical costs in the dominant hemisphere and lower cognitive costs in the left hemisphere (independent of handedness). In right-handed participants, both factors act agonistically to reduce the total cost of right-handed reaches. To distinguish between the cost factors, we had left- and right-hand-dominant participants execute a sequential, unimanual reaching task. Results showed a left-shift of the POC in the right-handed and a right-shift in the left-handed group. Both shifts were similar in magnitude. These findings indicate that only the mechanical cost of motor execution compensates for the disadvantages of the contralateral reaches, while the cognitive cost of motor planning is irrelevant for the POC shift.

Investigating the effect of handedness on the dental caries pattern, gingival index, and plaque index in 6-10 years old children.

Handedness is one of the individual characteristics that causes different mental and practical capabilities including different abilities to perform oral hygiene instructions. It seems that the right-handed and left-handed individuals have different ability in brushing and removing plaque at different areas of the mouth. To investigate the effect of handedness on decay pattern, gingival index, and plaque index in 6-10 years old children. In this cross-sectional study, children 6-10 years of age who fulfilled the inclusion criteria were selected. Dental caries and plaque and gingival indices were also measured and recorded for each child. Then the relationship between the handedness and the recorded variables was evaluated. Independent t-test and nonparametric Mann-Whitney test were used for the statistical comparison of quantitative variables between two right-handed and left-handed groups and Chi-square test was used for the statistical comparison of qualitative variables between these two groups. Data were analyzed using SPSS software version 20. The results showed that there was no significant relationship between any of the variables with being left- or right-handed. A significant relationship was observed only between the lowest plaque index and handedness (P < 0.05). A relationship cannot be considered between the handedness of children and their oral health status.

Right-hemispheric Dominance in Self-body Recognition is Altered in Left-handed Individuals

Visual self-face and proprioceptive postural recognition predominantly activate the right inferior frontoparietal cortices in human right-handers at the population level. In the present study, prompted by the finding that left-handedness may alter lateralized cortical organization for language, sensory-motor, and cognitive functions observed in right-handers, we investigated individual variations in right-dominant use of the cortices in 50 right-handers and 50 left-handers during self-body recognition (self-face and proprioceptive) tasks. We also investigated possible between-tasks differences in this right-dominant use, and possible atypical left–right reversed lateralization (right-dominance for language and left-dominance for self-body recognition) in left-handers. We measured brain activity using functional magnetic resonance imaging while participants performed a proprioceptive postural recognition task (experiencing illusory movements of the left and the right hands), a visual self-face recognition (self-other distinction) task, and a language (verb generation) task. To evaluate hemispheric dominance, we computed individual lateralization indices for the inferior frontoparietal activities in these tasks. Left-handedness altered the right-hemispheric dominance that was observed in the majority of right-handed participants in both self-body recognition tasks. In the left-handed group, during proprioceptive recognition, participants with right-lateralization, bilaterality, or left-lateralization were equally distributed, and during self-face recognition, right-lateralization was still observed, though the number of participants who demonstrated left-lateralization increased. Atypical left–right reversed lateralization was only observed in left-handed participants, but during both self-body recognition tasks. The present study provides novel and valuable knowledge about right-hemispheric dominance in self-body recognition affected by left-handedness. We discuss how functional lateralization of self-body recognition is shaped in human brain, in terms of handedness, language lateralization, and development.

Factors affecting the Mandarin dichotic digits test

Objective: Data with regard to the Mandarin dichotic digits test (DDT) are limited, with conflicting results reported between the Mandarin and English DDTs. The current study examined factors that might affect the performance in the Mandarin DDT.Design: The digits were arranged in 3 sets of 20 dichotic pairs; each set comprised 2, 3 or 4 digits in a pair.Study sample: Forty-one young, native Mandarin speakers with normal hearing were tested; 30 of them were right-handed and 11 left-handed. Six participants repeated the test.Results: The prevalence of ceiling effect in recognition score decreased systematically as the digit-pair length increased. At digit sets of 3-pair and 4-pair, the right-handed group showed a significant higher recognition score at right ear than left ear, while the left-handed group reversed the performance. The score difference between ears is significantly different between the right- and left-handed groups. The retest of the Mandarin DDT was reliable.Conclusions: For the right-handed group, a right-ear advantage can exist in the Mandarin DDT at a longer digit-pair length, similar to what was reported in the English DDT. Moreover, for the left-handed group, the attended right hemisphere in processing the tonal digits can result in a left-ear advantage.

Lateral differences in maximal grip strength in Czech male tennis players aged 11 – 12 in the context of injury prevention

The term laterality indicates the one-sided preference or functional advantage of the stronger, more accurate and coordinated limbs or organs and the brain hemisphere of a human body. In the preference process, more accurate, precise, coordinated and stronger side is chosen from the perspective of motoric functions. Among the general population is about 10-13% of left-handers and in certain sport fields this percentage may (baseball, tennis, box etc.). The left-handed dominance in tennis is considered an advantage. Due to unilateral load, there may be an excessive side-effect in strength differences in tennis and overloading of specific muscle group could lead to an injury. The aim of the research was to identify the levels of somatic and strength characteristics and assess the lateral difference in maximal grip strength of Czech elite male tennis players. The sample consisted of male tennis players, ranging in age from 11 to 12.9 years (n=186) who participated in the regular tests for Czech Tennis Association in years 2000-2018. Base anthropometrics were measured (height, weight) and maximal grip strength of both hands using the hand-held dynamometry (Grip D, Takei). Data came from normal distribution (statistically proven – chi-square test). The basic statistical characteristics were calculated (body height, M=155.08±7.98 cm; body weight, M=43.45±7.13 kg; strength of right hand: M=24.88±4.67 kp; strength of left hand: M=21.70±4.74 kp). It was found that 87.6% of the players (n=163) were right-handed and the remaining 12.4% left-handed (n=23). The assessment of the significance (Cohen´s d) between the dominant (playing) hand for the right-handed and left-handed players showed small effect size (dominant hand right: MRHR=25.11±4.41 kp, dominant hand left: MLHL=26.62±5.65 kp; d=0.30, small) in favor of the left-handed players. The difference between the dominant and the non-dominant hand showed large effect size for the right-handed (dominant hand right vs. hand left; MRHR=25.11±4.41 kp, MRHL=21.01±4.15 kp, d=0.96, large) and medium effect size for the left-handed players (dominant hand left vs. hand right; MLHL=26.62±5.65 kp, MLHR=23.24±5.98 kp, d=0.58, medium). The results showed that the value of 15 % level of strength laterality between dominant and non-dominant hand was exceeded for the right-handed (55.83 %) and left-handed (43.48%) groups ergo the exceeded value could be a cause of injuries. Because of this signals attention should be given during training process for optimizing the required load.

Visual and Auditory fMRI Paradigms for Presurgical Language Mapping: Convergent Validity and Relationship to Individual Variables.

Functional MRI (fMRI) has emerged as a safe alternative to invasive procedures for determining hemispheric language dominance prior to neurosurgery. Despite this, there are currently no standardized fMRI protocols that have been explored in healthy controls to determine the influence of individual patient variables on the results, which poses challenges in clinical interpretation of ambiguous findings in patient populations. In addition, most fMRI protocols are not suitable for individuals with visual or intellectual disabilities (IQ<70). In the current study, 61 healthy adults (ages: 18-74 years) completed two fMRI paradigms for language mapping. One paradigm used visually based stimuli and has shown good face validity to date in our center. The second paradigm used auditory stimuli presented at slowed speed and was designed for individuals with visual or cognitive dysfunction but has not yet been used clinically. The paradigms demonstrated 97% agreement in classifying individuals as left-hemisphere, right-hemisphere, and bilaterally dominant. Cases that were classified differently showed bilateral dominance in response to either paradigm. Dominance classification rates for right- and left-handed individuals were largely in keeping with published data. Within the left-handed group, IQ and education were positively correlated with laterality indices generated by both paradigms (r values range: 0.44-0.95, p<0.01), suggesting that individuals with higher IQ and formal education were more likely to be classified as left-hemisphere dominant in the current sample. This study will help improve clinical interpretation of language fMRI maps by identifying factors that might impact results (like IQ). It also offers an alternative paradigm to make this procedure more accessible to a broader range of patients. Future studies will replicate results with a sample of patients with epilepsy across a broad range of intellectual abilities.

An Investigation Into Handedness and Choking Under Pressure in Sport

ABSTRACTWhen athletes fail to perform at an expected level during an important moment, it is implied the athletes have experienced “choking“ (sudden decline in performance) under pressure.”. Researchers have reported that persistent left-hemispheric activation patterns occur when an athlete experiences considerable performance deteriorations under pressure. Researchers have also observed differences in brain activation patterns between left- and right-handed people on a variety of physical and cognitive tests, with the left-hemispheric activation more pronounced in right-handed participants. Purpose: The purpose of this study was to investigate whether athletes’ handedness may be linked to choking susceptibility (i.e., likelihood to experience performance decline under pressure). Method: Twenty right-handed and 13 left-handed experienced Australian football players completed 15 shot attempts, in both a low-pressure and a high-pressure condition. Both groups displayed equal state anxiety increases due to the pressure manipulation, indicating similar increases in anxiety in both handedness groups. Results: Differences were indicated in performance between the left- and right-handed groups during the high-pressure condition, with the left-handed group maintaining, and the right-handed participants declining, performance. Conclusion: Future electroencephalogram (EEG) research investigating this link may clarify the effect between handedness and choking.

Handedness and the Corpus Callosum: A Review and Further Analyses of Discordant Twins

Handedness effects with respect to regional corpus callosum (CC) anatomy remain open to question. Midsagittal CC tracings were obtained from structural MRIs in 21 female monozygotic twin pairs with discordant handedness (MZHd). The CC was divided into 99 percentile widths which were grouped into seven regions based on Denenberg’s (1989, 1991b) factor analysis. Results showed that left handed (LH) twins had significantly larger regional widths in CC region W22–39 compared to right handed (RH) twins, an effect present in 19/21 MZHd pairs. Cross-study analyses revealed CC W22–39 to have the highest variation across female singletons (Cowell et al., 1992, 1993). In the adjacent genu region (W3–18), CC size did not differ between RH and LH twins. However, when twins were reclassified according to handedness direction and consistency to form consistent RH, non-consistent RH, consistent LH and non-consistent LH groups, patterns of CC size in W3–18 closely matched those of singleton women (Cowell et al., 1993). Namely, CC W3–18 was larger in consistent compared to non-consistent RHs. Results support a claim that CC region W22–39, interconnecting premotor cortex in females, provides for environmentally influenced components of handedness, given the difference within MZHd twin pairs. By contrast, CC W3–18, connecting prefrontal cortex, was sensitive to direction and consistency of handedness, both in twins and singletons, a result consistent with combined genetic and environmental effects. Findings highlight the significance of MZHd twin studies in elucidating the developmental mechanisms underpinning structure–function asymmetry, cortical interconnectivity and neurodevelopmental bases of left hand preference.

S134. A comparative study of sensory nerve conduction velocity between right handed and left handed subjects

Nerve conduction study (NCS) is an objective neurophysiological test that measures nerve conduction velocity (CV). It is affected by various physiological factors like age, gender, height and temperature;however very minimal attention was directed towards the effect of limbdominance.The study aimed to compare sensory nerve conduction velocity between right-handed and left-handed subjects and between right and left sides within the same subject. Analytical cross sectional study done in the department of physiology, Faculty of Medicine of Khartoum University Involved 120 healthy students (60 right handed and 60 left handed). Bilateral NCS of Median and Ulnar sensory nerves was performed. No significant difference between CVs of right and left Median nerves in both right-handed (P = 0.5) and left-handed (P = 0.42) groups. Left Ulnar sensory nerve showed significantly higher CVs than the right Ulnar, in right-handed group (P = 0.003) as well as in left-handed group (P = 0.004). The left-handed group showed non significant higher velocities than right-handed group (P > 0.05). Ulnar nerves showed significantly higher conduction velocities on the left compared to the right side in both right-handed and left-handed groups but median nerve showed no difference. Again both Ulnar and Median sensory nerves CVs revealed no difference between right-handed and left-handed groups.

S180. A comparative study of motor nerves conduction velocity between right handed and left handed subjects

Motor Nerve conduction study is one of the electrophysiological tests performed to evaluate electrical conduction of motor nerves. Many studies involved nerve conduction velocity of peripheral nerves, but only few addressed this issue in relation to handedness with lots of controversies in their results. This Study was conducted to compare motor nerve conduction velocity between right-handed and left-handed subjects in large sample size. The study was carried as analytical cross-sectional study at the department of physiology, Faculty of Medicine, University of Khartoum and involved 120 healthy students from the medical campus, of whom 60 were right-handed and 60 were left-handed. Nerve conduction studies were performed using Medelec-Synergy machine. Two peripheral motor nerves of the upper limb (Median & Ulnar nerves) were investigated in each subject of the two groups bilaterally. The study revealed no significant difference in motor nerve conduction velocities of the investigated motor nerves (right-median, left-Median, right-ulnar & left-ulnar nerves) between the right-handed and the left-handed groups (P value > 0.05). Also when testing each group separately, no significant difference was found in motor nerve conduction velocities of the motor nerves (median, ulnar) between the right and left sides of the same subject, (P value > 0.05). The study concluded that there is no significant difference in nerve conduction velocity between right-handed and left-handed subjects. Same finding was found between right and left sides of the same subject, in both right-handed and left-handed groups. This proved that nerve conduction velocity has no relation with handedness.