Footedness is a better predictor of language lateralisation than handedness

Skeletal muscle fiber type and TMS-induced muscle relaxation in unfatigued and fatigued knee-extensor muscles

The force drop after transcranial magnetic stimulation (TMS) delivered to the motor cortex during voluntary muscle contractions could inform about muscle relaxation properties. Because of the physiological relation between skeletal muscle fiber-type distribution and size and muscle relaxation, TMS could be a noninvasive index of muscle relaxation in humans. By combining a noninvasive technique to record muscle relaxation in vivo (TMS) with the gold standard technique for muscle tissue sampling (muscle biopsy), we investigated the relation between TMS-induced muscle relaxation in unfatigued and fatigued states, and muscle fiber-type distribution and size. Sixteen participants (7F/9M) volunteered to participate. Maximal knee-extensor voluntary isometric contractions were performed with TMS before and after a 2-min sustained maximal voluntary isometric contraction. Vastus lateralis muscle tissue was obtained separately from the participants' dominant limb. Fiber type I distribution and relative cross-sectional area of fiber type I correlated with TMS-induced muscle relaxation at baseline (r = 0.67, adjusted P = 0.01; r = 0.74, adjusted P = 0.004, respectively) and normalized TMS-induced muscle relaxation as a percentage of baseline (r = 0.50, adjusted P = 0.049; r = 0.56, adjusted P = 0.031, respectively). The variance in the normalized peak relaxation rate at baseline (59.8%, P < 0.001) and in the fatigue resistance (23.0%, P = 0.035) were explained by the relative cross-sectional area of fiber type I to total fiber area. Fiber type I proportional area influences TMS-induced muscle relaxation, suggesting TMS as an alternative method to noninvasively inform about skeletal muscle relaxation properties.NEW & NOTEWORTHY Transcranial magnetic stimulation (TMS)-induced muscle relaxation reflects intrinsic muscle contractile properties by interrupting the drive from the central nervous system during voluntary muscle contractions. We showed that fiber type I proportional area influences the TMS-induced muscle relaxation, suggesting that TMS could be used for the noninvasive estimation of muscle relaxation in unfatigued and fatigued human muscles when the feasibility of more direct method to study relaxation properties (i.e., muscle biopsy) is restricted.

Sex differences in neuromuscular and biological determinants of isometric maximal force

AIM

Force expression is characterized by an interplay of biological and molecular determinants that are expected to differentiate males and females in terms of maximal performance. These include muscle characteristics (muscle size, fiber type, contractility), neuromuscular regulation (central and peripheral factors of force expression), and individual genetic factors (miRNAs and gene/protein expression). This research aims to comprehensively assess these physiological variables and their role as determinants of maximal force difference between sexes.

METHODS

Experimental evaluations include neuromuscular components of isometric contraction, intrinsic muscle characteristics (proteins and fiber type), and some biomarkers associated with muscle function (circulating miRNAs and gut microbiome) in 12 young and healthy males and 12 females.

RESULTS

Male strength superiority appears to stem primarily from muscle size while muscle fiber-type distribution plays a crucial role in contractile properties. Moderate-to-strong pooled correlations between these muscle parameters were established with specific circulating miRNAs, as well as muscle and plasma proteins.

CONCLUSION

Muscle size is crucial in explaining the differences in maximal voluntary isometric force generation between males and females with similar fiber type distribution. Potential physiological mechanisms are seen from associations between maximal force, skeletal muscle contractile properties, and biological markers.

Effects of rhythmic visual cues on cortical activation and functional connectivity features during stepping: an fNIRS study

Introduction

Rhythmic visual cues (RVCs) may influence gait initiation by modulating cognition resources. However, it is unknown how RVCs modulate cognitive resources allocation during gait movements. This study focused on investigating the effects of RVCs on cortical hemodynamic response features during stepping to evaluate the changes of cognitive resources.

Methods

We recorded cerebral hemoglobin concentration changes of 14 channels in 17 healthy subjects using functional near-infrared spectroscopy (fNIRS) during stepping tasks under exposure to RVCs and non-rhythmic visual cues (NRVCs). We reported mean oxygenated hemoglobin (HbO) concentration changes, β-values, and functional connectivity (FC) between channels.

Results

The results showed that, the RVC conditions revealed lower HbO responses compared to the NRVC conditions during the preparation and early stepping. Correspondingly, the β-values reflected that RVCs elicited lower hemodynamic responses than NRVCs, and there was a decreasing trend in stimulus-evoked cortical activation as the task progressed. However, the FC between channels were stronger under RVCs than under NRVCs during the stepping progress, and there were more significant differences in FC during the early stepping.

Discussion

In conclusion, there were lower cognitive demand and stronger FC under RVC conditions than NRVC conditions, which indicated higher efficiency of cognitive resources allocation during stepping tasks. This study may provide a new insight for further understanding the mechanism on how RVCs alleviate freezing of gait.

Lateral spatial biases in naturalistic and simulated driving: Does pseudoneglect influence performance?

Whereas a rightward bump is more likely than a leftward bump when walking through a doorway, investigations into potential similar asymmetries for drivers are limited. The research presented here aims to determine the influence of innate lateral spatial biases when driving. Data from the Strategic Highway Research Program Naturalistic Driving Study (SHRP 2 NDS) and a driving simulation were used to address our research questions. Data points from SHRP 2 were aggregated within relevant variables (e.g., left/right obstacles). In the simulation, participants drove in ways that were consistent with their everyday driving in urban and rural environments. Collision frequency, collision severity and average lateral lane position were analyzed with rightward biases throughout both analyzes. SHRP 2 data indicated greater likelihoods of collisions when vehicles crossed the right line/edge of the road and when making a right turn. There were more collisions with obstacles on the right side, which were also more severe, and greater rightward lane deviations in the driving simulation, contrasted with more severe collisions on the left side in SHRP 2 data, possibly because of the presence of traffic. These findings suggest that previously observed rightward biases in distant space when walking are also present when driving.

Inventories of Human Lateral Preference: A Systematic Review

There are a variety of inventories available to evaluate human lateral preference, but no previous review has systematically analyzed and compared them. We conducted a systematic literature review to identify these inventories and describe their characteristics (e.g., dimensions, scales, tasks, psychometric properties). We included 26 articles, each presenting a different inventory to assess lateral preference, published between 1900 and 2022, selected from the following databases: PubMed, SportDiscus, APA PsycNET, and Web of Science. These inventories analyzed tasks performed in everyday life (domestic, work-related, sports, and leisure/recreation activities), covering hand, foot, hearing, visual and other non-usual lateral preference dimensions, such as trunk and head. Most inventories classified individuals based on the direction (left, indifferent or right preference) and degree (consistent or moderate) of laterality. However, many of the reviewed inventories lack established psychometric verification in their original publication, such as validity, reliability, responsiveness, and practical applicability. Inventories also presented tasks that may be specific to a given cultural setting, limiting their application across different countries. Based on these findings, we provide a comprehensive guide for researchers to select a lateral preference assessment tool, but also advocate for a new inventory with a broader approach, containing more than one dimension of lateral preference (i.e., not only handedness) and tasks that are common to different cultures to enhance practical applicability worldwide.

Assessing non-right-handedness and atypical cerebral lateralisation as predictors of paediatric mental health difficulties

Research utilising handedness as a proxy for atypical language lateralisation has invoked the latter to explain increased mental health difficulties in left-/mixed-handed children. The current study investigated unique associations between handedness and language lateralisation, handedness and mental health, and language lateralisation and mental health, in children, to elucidate the role of cerebral lateralisation in paediatric mental health. Participants were N = 64 (34 females [52%]; MAge  = 8.56 years; SDAge  = 1.33; aged 6-12 years) typically developing children. Hand preference was assessed via a reaching task, language lateralisation was assessed using functional transcranial Doppler ultrasonography (fTCD) during an expressive language task, and mental health was assessed with the Strengths and Difficulties Questionnaire. As hypothesised, leftward hand preference predicted increased general mental health issues in children, with a strong relationship noted between leftward hand preference and the emotional symptoms subscale. Contrary to expectation, no relationship was found between direction of language lateralisation and general mental health issues, although exploratory analyses of subscales showed rightward lateralisation to predict conduct problems. Hand preference and direction of language lateralisation were also not significantly associated. The relatively weak relationship between manual and language laterality coupled with discrepancy regarding the predictive scope of each phenotype (i.e., hand preference predicts overall mental health, whereas language laterality predicts only conduct problems) suggests independent developmental pathways for these phenotypes. The role of manual laterality in paediatric mental health warrants further investigation utilising a neuroimaging method with higher spatial resolution.

Unintentional force drifts in the lower extremities

We explored the phenomenon of unintentional force drift seen in the absence of visual feedback during knee extension contractions in isometric conditions. Based on the importance of knee extensors for the anti-gravity function, we hypothesized that such force drifts would be slower and smaller compared to those reported for the upper extremities. We also explored possible effects of foot dominance and gender on the force drifts. Young healthy persons produced isometric knee extension contractions to different levels, ranging from 15 to 25% of maximal voluntary contraction force, with the help of visual feedback, and then, the visual feedback was turned off. Force change over the time interval without visual feedback was quantified. In the absence of visual feedback, force drifted to smaller magnitudes. The drift magnitude expressed in percent of the initial force magnitude was smaller for smaller initial force levels, ranging between 8 and 15% of the initial force for the initial force magnitude of 15% and 25% of maximal voluntary contraction force. The time exponent of the force drift was independent of the initial force magnitude and was, on average, 6.45 s. There were no significant effects of foot dominance or gender, although the male subjects tended to show stronger scaling of the drift magnitude with the initial force level compared to the female subjects. The results show that unintentional force drift is a common phenomenon across limbs and muscle groups. This conclusion fits the theory of control with spatial referent coordinates and the general tendency of all natural systems to drift to states with lower potential energy.

Bilateral Training Improves Agility and Accuracy for Both Preferred and Non-Preferred Legs in Young Soccer Players

As laterality of the lower limbs is regarded as a relevant influence on soccer performance, we assessed whether a bilateral training program for both the preferred leg (PL) and non-preferred leg (NPL) would improve soccer players' lateral asymmetry, agility, and accuracy. Sixty right-foot-dominant young soccer players were randomly assigned to either an experimental group (EXP) that underwent bilateral training or a control group (CONT) that performed their usual training schedule without bilateral exercise. We assessed the players' lateral asymmetries before and after training on four soccer skill tasks: a zigzag test with and without a ball, a receiving and direct volley-shooting accuracy test, and a passing accuracy test. Results showed post-test versus pre-test performance improvements for the EXP group on the index of technical skills and agility (p < .001). A post-hoc analysis further revealed a pre-test to post-test performance improvement on shooting and passing accuracy with both legs only for the EXP group (p < .001). These results support the role of bilateral practice in improving lateral asymmetries, agility, and accuracy.

Human Lateralization, Maternal Effects and Neurodevelopmental Disorders

In humans, behavioral laterality and hemispheric asymmetries are part of a complex biobehavioral system in which genetic factors have been repeatedly proposed as developmental determinants of both phenomena. However, no model solely based on genetic factors has proven conclusive, pushing towards the inclusion of environmental and epigenetic factors into the system. Moreover, it should be pointed out that epigenetic modulation might also account for why certain genes are expressed differently in parents and offspring. Here, we suggest the existence of a sensitive period in early postnatal development, during which the exposure to postural and motor lateral biases, expressed in interactive sensorimotor coordination with the caregiver, canalizes hemispheric lateralization in the “typical” direction. Despite newborns and infants showing their own inherent asymmetries, the canalizing effect of the interactive context owes most to adult caregivers (usually the mother), whose infant-directed lateralized behavior might have been specifically selected for as a population-level trait, functional to confer fitness to offspring. In particular, the case of the left-cradling bias (LCB; i.e., the population-level predisposition of mothers to hold their infants on the left side) represents an instance of behavioral trait exhibiting heritability along the maternal line, although no genetic investigation has been carried out so far. Recent evidence, moreover, seems to suggest that the reduction of this asymmetry is related to several unfavorable conditions, including neurodevelopmental disorders. Future studies are warranted to understand whether and how genetic and epigenetic factors affect the lateralization of early mother-infant interaction and the proneness of the offspring to neurodevelopmental disorders.

Age-associated increase in postural variability relate to greater low-frequency center of pressure oscillations

BACKGROUND

Postural control is impaired in older adults, as evidenced from greater variability of the center of pressure (COP) during postural tasks. Although COP variability associates with low-frequency COP oscillations (<1 Hz) in young adults, it remains unknown if the age-associated increase in COP variability relates to greater low-frequency COP oscillations.

RESEARCH QUESTION

Do low-frequency oscillations contribute to greater postural sway (center of pressure (COP) variability) in older adults when attempting to voluntarily maintain posture in a forward leaning position compared to young adults?

METHODS

Seven young (25.7 ± 4.8) and seven older (71.0 ± 7.0) adults performed a postural lean forward task and attempted to match a COP target in the anterior-posterior direction as steady as possible. We quantified the COP variability as the standard deviation (SD) of COP displacements in the anterior-posterior and medial-lateral directions and quantified the frequency modulation of COP as the power in COP displacement spectra from 0-1 Hz.

RESULTS

We found that older adults had significantly greater anterior-posterior SD of COP (p = 0.027) and power below 0.5 Hz (p = 0.048) than young adults, but power from 0.5-1 Hz was similar (p = 0.083). In contrast, the medial-lateral SD of COP (p = 0.5) and power from 0-1 Hz (p = 0.228) was similar for the two age groups. For both the anterior-posterior and medial-lateral direction, the SD of COP was related to low frequency oscillations below 0.5 Hz.

SIGNIFICANCE

For the first time, we show that the age-associated increase in postural variability relates to greater COP oscillations below 0.5 Hz.

The Bias toward the Right Side of Others Is Stronger for Hands than for Feet

As shown by a series of previous studies, ambiguous human bodies performing unimanual or unipedal actions tend to be perceived more frequently as right-handed or right-footed rather than left-handed or left-footed, which indicates a perceptual and attentional bias toward the right side of others’ body. However, none of such studies assessed whether the relative strength of such a bias differs between the upper and lower limbs. Indeed, given that the prevalence of right-handedness is slightly larger than that of right-footedness, and given that hands provide more information than feet as regards both communicative and aggressive acts, it is plausible that the bias toward the right side of human bodies should be stronger for the hand than for the foot. We performed three experiments in each of which participants had to indicate the rotating direction (revealing the perceived handedness/footedness) of ambiguous human figures with either one limb (arm or leg) or two limbs (one arm and the contralateral leg) extended. The hypothesized advantage of the right hand over the right foot was found in both the second and the third experiment.

Four meta-analyses across 164 studies on atypical footedness prevalence and its relation to handedness

Human lateral preferences, such as handedness and footedness, have interested researchers for decades due to their pronounced asymmetries at the population level. While there are good estimates on the prevalence of handedness in the population, there is no large-scale estimation on the prevalence of footedness. Furthermore, the relationship between footedness and handedness still remains elusive. Here, we conducted meta-analyses with four different classification systems for footedness on 145,135 individuals across 164 studies including new data from the ALSPAC cohort. The study aimed to determine a reliable point estimate of footedness, to study the association between footedness and handedness, and to investigate moderating factors influencing footedness. We showed that the prevalence of atypical footedness ranges between 12.10% using the most conservative criterion of left-footedness to 23.7% including all left- and mixed-footers as a single non-right category. As many as 60.1% of left-handers were left-footed whereas only 3.2% of right-handers were left-footed. Males were 4.1% more often non-right-footed compared to females. Individuals with psychiatric and neurodevelopmental disorders exhibited a higher prevalence of non-right-footedness. Furthermore, the presence of mixed-footedness was higher in children compared to adults and left-footedness was increased in athletes compared to the general population. Finally, we showed that footedness is only marginally influenced by cultural and social factors, which play a crucial role in the determination of handedness. Overall, this study provides new and useful reference data for laterality research. Furthermore, the data suggest that footedness is a valuable phenotype for the study of lateral motor biases, its underlying genetics and neurodevelopment.

A large-scale estimate on the relationship between language and motor lateralization

Human language is dominantly processed in the left cerebral hemisphere in most of the population. While several studies have suggested that there are higher rates of atypical right-hemispheric language lateralization in left-/mixed-handers, an accurate estimate of this association from a large sample is still missing. In this study, we comprised data from 1,554 individuals sampled in three previous studies in which language lateralization measured via dichotic listening, handedness and footedness were assessed. Overall, we found a right ear advantage indicating typical left-hemispheric language lateralization in 82.1% of the participants. While we found significantly more left-handed individuals with atypical language lateralization on the categorical level, we only detected a very weak positive correlation between dichotic listening lateralization quotients (LQs) and handedness LQs using continuous measures. Here, only 0.4% of the variance in language lateralization were explained by handedness. We complemented these analyses with Bayesian statistics and found no evidence in favor of the hypothesis that language lateralization and handedness are related. Footedness LQs were not correlated with dichotic listening LQs, but individuals with atypical language lateralization also exhibited higher rates of atypical footedness on the categorical level. We also found differences in the extent of language lateralization between males and females with males exhibiting higher dichotic listening LQs indicating more left-hemispheric language processing. Overall, these findings indicate that the direct associations between language lateralization and motor asymmetries are much weaker than previously assumed with Bayesian correlation analyses even suggesting that they do not exist at all. Furthermore, sex differences seem to be present in language lateralization when the power of the study is adequate suggesting that endocrinological processes might influence this phenotype.

Virtual Reality Immersion in Healthy Individuals: Ellipse Sway Area of an Electrical Shuttle Balance

To assess indirectly the effects of virtual reality (VR) immersion on postural sway in thirteen healthy individuals. The ellipse sway area was recorded with an accelerometer coupled to an electrical shuttle balance under six conditions, varying Romberg and single leg stance (SLS) position with eyes open and eyes closed. The length of the ellipse traveled over 10 s was measured and Romberg and single leg stance (SLS) ratios were calculated. Ellipse sway area was reduced in all positions after VR intervention. Statistical differences were observed in the left SLS ratio 24 hr after comparison to the baseline. A single VR session could reduce ellipse sway area and decrease the visual dependency of posture control indicating increased ability to maintain stable body sway over the shuttle.

Quadriceps muscle compensatory activations are delayed following anterior cruciate ligament reconstruction using hamstring tendon graft

BACKGROUND

Compensatory and anticipatory quadriceps activation (CQA and AQA) in response to postural perturbations are essential for functional stability of the knee. This study aimed at investigating CQA and AQA before and after anterior cruciate ligament reconstruction (ACLR) using hamstrings graft.

METHODS

Twelve participants with ACLR and 12 healthy controls were exposed to 10 either unpredictable or predictable perturbations of the knee before ACLR (T1), two months (T2) and six months (T3) after surgery. Latencies of CQA and AQA in vastus lateralis (VL), rectus femoris (RF) and vastus medialis (VM) were measured.

RESULTS

Latency of CQA was delayed in ACLR compared to controls at T1 for VL (105 ± 25 vs. 57 ± 9 ms; P < .001), RF (102 ± 23 vs. 56 ± 9 ms; P < .001) and VM (107 ± 24 vs. 66 ± 16 ms; P < .001), at T2 for VL (68 ± 14 vs. 55 ± 10 ms; P < .01) and at T3 for VL (105 ± 22 vs. 58 ± 7 ms; P < .001), RF (102 ± 22 vs. 58 ± 12 ms; P < .001) and VM (106 ± 20 vs. 63 ± 8 ms; P < .001). AQA occurred earlier in ACLR than in controls at T1 for VL (-82 ± 64 vs. -14 ± 11 ms; P < .05) and VM (-105 ± 68 vs. -9 ± 12 ms; P < .05).

CONCLUSION

CQA are delayed following ACLR with hamstring graft and should be addressd by post-surgical rehabilitation.

Are Footedness and Lateral Postures Better Predictors of Hemispheric Dominance Than Handedness: A Cross-sectional Questionnaire-Based Clinical and Pedigree Study

Objective  Approximately 9 out of 10 individuals show right-hand dominance. The remaining 10% include left-hand dominant and mixed handed/ambidextrous individuals. Laterality, lateral postures or lateral preference is defined by various authors as the most comfortable posture that an individual prefers to assume. The current study aims at finding the distribution of these lateral postures and their correlation with handedness/dominant side.

Materials and Methods  The study was done in medical and nursing students in the age group 18 to 22 years. The patients were asked to fill a self-assessment questionnaire to determine handedness and footedness. The laterality traits were observed by asking the patients to do by themselves after an untailored demonstration.

Statistical Analysis  The relationship between study parameters was assessed using Chi-square test. Pearson’s correlation test was done to assess the strength of association between comfort ratings of the various laterality postures.

Results  In our study, 96.5% were right handed and 79.9% of patients were right footed. Also, 50.8% preferred right-hand clasping, 53.9% preferred left-arm folding, and 60.6% preferred right-leg folding. A statistically significant correlation was seen between foot preference and lateral postures and arm folding and hand clasping (p < 0.05). A significant association was also found between handedness and positive history of retraining. Sidedness did not follow any Mendelian pattern of inheritance.

Conclusions  Handedness is affected by genetic and environmental factors. Since cultural and traditional practices can affect the lateral postures and handedness, it is important to know the relationship between laterality postures and sidedness and the impact of retraining on them. These postures are measures of cerebral dominance and are clinically important.

Hair Whorl Direction: The Association with Handedness, Footedness, and Eyedness

Hair whorl direction and handedness were stated to have a common genetic basis in the random recessive model. This study was carried out with a total of 317 healthy young males. The association between hair whorl swirling direction and handedness, footedness and eyedness were assessed. The direction of hair whorl was clockwise at a rate of 76.7%, and counter clock wise at a rate of 23.3%. There was no significant association between hair whorl direction and handedness, footedness, and eyedness (p > .05). The results indicate that hair whorl swirling direction is not an evident marker of functional laterality.

Reaction to a Visual Stimulus: Anticipation with Steady and Dynamic Contractions

Reacting fast to visual stimuli is important for many activities of daily living and sports. It remains unknown whether the strategy used during the anticipatory period influences the speed of the reaction. The purpose of this study was to determine if reaction time (RT) differs following a steady and a dynamic anticipatory strategy. Twenty‐two young adults (21.0 ± 2.2 yrs, 13 women) participated in this study. Participants performed 15 trials of a reaction time task with ankle dorsiflexion using a steady (steady force at 15% MVC) and a dynamic (oscillating force from 10‐20% MVC) anticipatory strategy. We recorded primary agonist muscle (tibialis anterior; TA) electromyographic (EMG) activity. We quantified RT as the time interval from the onset of the stimulus to the onset of force. We found that a dynamic anticipatory strategy, compared to the steady anticipatory strategy, resulted in a longer RT (p = 0.04). We classified trials of the dynamic condition based on the level and direction of anticipatory force at the moment of the response. We found that RT was longer during the middle descending relative to the middle ascending and the steady conditions (p < 0.01). All together, these results suggest that RT is longer when preceded by a dynamic anticipatory strategy. Specifically, the longer RT is a consequence of the variable direction of force at which the response can occur, which challenges the motor planning process.

Age-related changes in proprioception of the ankle complex across the lifespan

BACKGROUND

Ankle complex proprioceptive ability, needed in active human movement, may change from childhood to elderly adulthood; however, its development across all life stages has remained unexamined. The aim of the present study was to investigate the across-the-lifespan trend for proprioceptive ability of the ankle complex during active ankle inversion movement.

METHODS

The right ankles of 118 healthy right-handed participants in 6 groups were assessed: children (6-8 years old), adolescents (13-15 years old), young adults (18-25 years old), middle-aged adults (35-50 years old), old adults (60-74 years old), and very old adults (75-90 years old). While the participants were standing, their ankle complex proprioception was measured using the Active Movement Extent Discrimination Apparatus.

RESULTS

There was no significant interaction between the effects of age group and gender on ankle proprioceptive acuity (F (5, 106) = 0.593, p = 0.705, η² _p = 0.027). Simple main effects analysis showed that there was a significant main effect for age group (F (5, 106) = 22.521, p < 0.001, η ² _p = 0.515) but no significant main effect for gender (F (1,106) =  2.283, p = 0.134, η ² _p = 0.021) between the female (0.723 ± 0.092, mean ± SD) and the male (0.712 ± 0.083) participants. The age-group factor was associated with a significant linear downward trend in scores (F (1, 106) = 10.584, p = 0.002, η ² _p = 0.091) and a strong quadratic trend component (F (1,106) = 100.701, p < 0.001, η ² _p = 0.480), producing an asymmetric inverted-U function.

CONCLUSION

The test method of the Active Movement Extent Discrimination Apparatus is sensitive to age differences in ankle complex proprioception. For proprioception of the ankle complex, young adults had significantly better scores than children, adolescents, old adults, and very old adults. The middle-aged group had levels of ankle proprioceptive acuity similar to those of the young adults. The scores for males and females were not significantly different. Examination of the range of the scores in each age group highlights the possible level that ankle complex movement proprioceptive rehabilitation can reach, especially for those 75-90 years of age.

No Evidence That Lateral Preferences Predict Individual Differences in the Tendency to Update Mental Representations: A Replication-Extension Study

A growing body of evidence suggests that inconsistent hand preference is indicative of an increased disposition to update one’s beliefs upon exposure to novel information. This is attributed to a facilitated exchange of information between the two brain hemispheres among inconsistent handers, compared to consistent handers. Currently available studies provide only indirect evidence for such an effect, were mostly based on small sample sizes, and did not provide measures of effect size. Small sample size is a major factor contributing to low replicability of research findings and false-positive results. We thus attempted to replicate Experiment 1 of Westfall, Corser and Jasper (2014), which appears to be representative of research on degree of handedness and belief updating in terms of the employed methods. We utilized data from a sample more than 10 times the size (N = 1243) of the original study and contrasted the commonly applied median-split technique to classify inconsistent and consistent handers with an empirically grounded classification scheme. Following a replication-extension approach, besides handedness, footedness was also explored. Only one out of 12 chi-squared tests reached significance and supported the original hypothesis that inconsistent handers stay with, or switch more often from, the status quo than consistent handers, depending on the valence of novel information. A small-telescopes analysis suggested that the original study had too low analytic power to detect its reported effect reliably. These results cast doubt on the assumption that inconsistent and consistent-handers differ in the tendency to update mental representations. We discuss the use of the median-split technique in handedness research, available neuroscientific evidence on interhemispheric interaction and inconsistent handedness, and venues of future research.

Foot preference across the lifespan: Effects of target location and task complexity

This study was designed to determine the factor(s) that influence the choice of the foot throughout the lifespan. To achieve this purpose, 86 right-footed participants (young children (5– 8), adolescents (10–14), young adults (18–25) and older adults (over 50) were tested on two tasks of different levels of difficulty, performed in three spatial locations (left, right, and midline) according to two levels of body posture: sitting and standing. Results revealed that the participants favored their preferred foot when the object was located in the ipsilateral hemispace and at the midline. They selected their non-preferred foot when the object was located in the contralateral hemispace. The participants used their preferred foot to a greater extent during the most complex task than during the easiest one and more often while standing rather than sitting. Finally, we have found a significant age effect. Young children often used the preferred foot more frequently than the other age groups. In conclusion, the findings of this study suggest that foot selection depends on task demand, environmental constraints, and a biological factor associated with motor dominance.

Kinematic effects of repeated turns while running

In team sports, non-contact ACL and MCL injuries occur during abrupt changes of direction, like turns or cutting manoeuvres. Fatigue affects dynamic neuromuscular control and increases knee injury risk. This study analysed how lower limb joints and centre-of-mass kinematics are affected throughout a high-intensity running protocol involving repeated 180°-turns. Twenty young men (18-23 years, BMI: 20.8-24.4 kg m^-2) completed a 5-m shuttle running trial lasting 5 min at an average speed of 75% of their maximum aerobic speed. During the test, cardio-metabolic parameters were obtained, together with joints and centre-of-mass kinematics, using a motion capture system. Kinematic data were compared between the first and the last minute of exercise. Perceived exercise intensity ranged from "hard" to "maximum exertion" and post-exercise lactate concentration ranged from 5.4 to 15.5 mM. The repetition of 180°-turns induced a substantial reduction of hip (-60%, p < .001, large effect) and knee flexion (-40%, p = .003, medium-to-large effect), and an increase of hip adduction and internal rotation (+25-30%, p < .05, medium-to-large effect). Since such movements are factors increasing the likelihood of non-contact knee injuries, we concluded that the prolonged repetition of turns may expose participants to increased risk of ligament failure. Prevention programmes should include discipline-specific neuromuscular training especially in late practices.

Motor planning perturbation: muscle activation and reaction time

Reaction time (RT) is the time interval between the appearance of a stimulus and initiation of a motor response. Within RT, two processes occur, selection of motor goals and motor planning. An unresolved question is whether perturbation to the motor planning component of RT slows the response and alters the voluntary activation of muscle. The purpose of this study was to determine how the modulation of muscle activity during an RT response changes with motor plan perturbation. Twenty-four young adults (20.5 ±1.1 yr, 13 women) performed 15 trials of an isometric RT task with ankle dorsiflexion using a sinusoidal anticipatory strategy (10-20% maximum voluntary contraction). We compared the processing part of the RT and modulation of muscle activity from 10 to 60 Hz of the tibialis anterior (primary agonist) when the stimulus appeared at the trough or at the peak of the sinusoidal task. We found that RT ( P = 0.003) was longer when the stimulus occurred at the peak compared with the trough. During the time of the reaction, the electromyography (EMG) power from 10 to 35 Hz was less at the peak than the trough ( P = 0.019), whereas the EMG power from 35 to 60 Hz was similar between the peak and trough ( P = 0.92). These results suggest that perturbation to motor planning lengthens the processing part of RT and alters the voluntary activation of the muscle by decreasing the relative amount of power from 10 to 35 Hz. NEW & NOTEWORTHY We aimed to determine whether perturbation to motor planning would alter the speed and muscle activity of the response. We compared trials when a stimulus appeared at the peak or trough of an oscillatory reaction time task. When the stimulus occurred at the trough, participants responded faster, with greater force, and less EMG power from 10-35 Hz. We provide evidence that motor planning perturbation slows the response and alters the voluntary activity of the muscle.

Effects of side-dominance on knee joint proprioceptive target-matching asymmetries

AIMS

Right- and left-side-dominant individuals reveal target-matching asymmetries between joints of the dominant and non-dominant upper limbs. However, it is unclear if such asymmetries are also present in lower limb's joints. We hypothesized that right-side-dominant participants perform knee joint target-matching tasks more accurately with their non-dominant leg compared to left-side-dominant participants.

METHODS

Participants performed position sense tasks using each leg by moving each limb separately and passively on an isokinetic dynamometer.

RESULTS

Side-dominance affected (p < 0.05) knee joint absolute position errors only in the non-dominant leg but not in the dominant leg: right-side-dominant participants produced less absolute position errors (2.82° ± 0.72°) with the non-dominant leg compared to left-side-dominant young participants (3.54° ± 0.33°).

CONCLUSIONS

In conclusion, right-side-dominant participants tend to perform a target-matching task more accurately with the non-dominant leg compared to left-side-dominant participants. Our results extend the literature by showing that right-hemisphere specialization under proprioceptive target-matching tasks may be not evident at the lower limb joints.

Decomposing sensorimotor variability changes in ageing and their connection to falls in older people

The relationship between sensorimotor variability and falls in older people has not been well investigated. We developed a novel task having shared biomechanics of obstacle negotiation to quantify sensorimotor variability related to locomotion across age. We found that sensorimotor variability in foot placement increases continuously with age. We then applied sensory psychophysics to pinpoint the visual and somatosensory systems associated with sensorimotor variability. We showed increased sensory variability, specifically increased proprioceptive variability, the vital cause of more variable foot placement in older people (greater than 65 years). Notably, older participants relied more on the vision to judge their own foot’s height compared to the young, suggesting a shift in multisensory integration strategy to compensate for degenerated proprioception. We further modelled the probability of tripping-over based on the relationship between sensorimotor variability and age and found a correspondence between model prediction and community-based data. We reveal increased sensorimotor variability, modulated by sensation precision, a potentially vital mechanism of raised tripping-over and thus fall events in older people. Analysis of sensorimotor variability and its specific components may have the utility of fall risk and rehabilitation target evaluation.

Oscillatory Corticospinal Activity during Static Contraction of Ankle Muscles Is Reduced in Healthy Old versus Young Adults

Aging is accompanied by impaired motor function, but age-related changes in neural networks responsible for generating movement are not well understood. We aimed to investigate the functional oscillatory coupling between activity in the sensorimotor cortex and ankle muscles during static contraction. Fifteen young (20–26 yr) and fifteen older (65–73 yr) subjects were instructed to match a target force by performing static ankle dorsi- or plantar flexion, while electroencephalographic (EEG) activity was recorded from the cortex and electromyographic (EMG) activity was recorded from dorsi- (proximal and distal anterior tibia) and plantar (soleus and medial gastrocnemius) flexor muscles. EEG-EMG and EMG-EMG beta band (15–35 Hz) coherence was analyzed as an index of corticospinal activity. Our results demonstrated that beta cortico-, intra-, and intermuscular coherence was reduced in old versus young subjects during static contractions. Old subjects demonstrated significantly greater error than young subjects while matching target forces, but force precision was not related to beta coherence. We interpret this as an age-related decrease in effective oscillatory corticospinal activity during steady-state motor output. Additionally, our data indicate a potential effect of alpha coherence and tremor on performance. These results may be instrumental in developing new interventions to strengthen sensorimotor control in elderly subjects.

Footedness Is Associated With ADHD Symptoms in the Adult General Population

OBJECTIVE

Mixed-handedness among children has recently been proposed as a marker of neurodevelopmental disorder and ADHD. This study expanded this initial evidence to the questions of whether mixed-handedness as well as mixed-footedness are similarly associated with ADHD among adults.

METHOD

Self-reported ADHD symptoms, handedness, footedness, and current depression and anxiety were assessed in a large, heterogeneous general population sample ( N = 2,592). Latent variable analysis was used to investigate the structure and measurement properties of ADHD symptoms, the dimensionality of footedness, and the classification of lateral preferences.

RESULTS

Mixed-footedness was associated with probable ADHD (odds ratio [OR] = 1.76 [1.07, 2.89], p = .026). Left- and mixed-footedness were associated with higher inattention and impulsivity scores.

CONCLUSION

Developmental continuities of the associations of mixed lateral preferences with ADHD from child to adult age seem to exist. In particular, mixed-footedness, rather than mixed-handedness, appears to be an ADHD marker among adults.

Translation, cultural adaption, and test-retest reliability of Chinese versions of the Edinburgh Handedness Inventory and Waterloo Footedness Questionnaire

Quantitative assessments of handedness and footedness are often required in studies of human cognition and behaviour, yet no reliable Chinese versions of commonly used handedness and footedness questionnaires are available. Accordingly, the objective of the present study was to translate the Edinburgh Handedness Inventory (EHI) and the Waterloo Footedness Questionnaire-Revised (WFQ-R) into Mandarin Chinese and to evaluate the reliability and validity of these translated versions in healthy Chinese people. In the first stage of the study, Chinese versions of the EHI and WFQ-R were produced from a process of translation, back translation and examination, with necessary cultural adaptations. The second stage involved determining the reliability and validity of the translated EHI and WFQ-R for the Chinese population. One hundred and ten Chinese participants were tested online, and the results showed that the Cronbach's alpha coefficient of internal consistency was 0.877 for the translated EHI and 0.855 for the translated WFQ-R. Another 170 Chinese participants were tested and re-tested after a 30-day interval. The intra-class correlation coefficients showed high reliability, 0.898 for the translated EHI and 0.869 for the translated WFQ-R. This preliminary validation study found the translated versions to be reliable and valid tools for assessing handedness and footedness in this population.

Motor plan differs for young and older adults during similar movements

Older adults exhibit altered activation of the agonist and antagonist muscles during goal-directed movements compared with young adults. However, it remains unclear whether the differential activation of the antagonistic muscles in older adults results from an impaired motor plan or an altered ability of the muscle to contract. The purpose of this study, therefore, was to determine whether the motor plan differs for young and older adults. Ten young (26.1 ± 4.3 yr, 4 women) and 16 older adults (71.9 ± 6.9 yr, 9 women) participated in the study. Participants performed 100 trials of fast goal directed movements with ankle dorsiflexion while we recorded the electromyographic activity of the primary agonist (tibialis anterior; TA) and antagonist (soleus; SOL) muscles. From those 100 trials we selected 5 trials in each of 3 movement end-point categories (fast, accurate, and slow). We investigated age-associated differences in the motor plan by quantifying the individual activity and coordination of the agonist and antagonist muscles. During similar movement end points, older adults exhibited similar activation of the agonist (TA) and antagonist (SOL) muscles compared with young adults. In addition, the coordination of the agonist and antagonist muscles (TA and SOL) was different between the two age groups. Specifically, older adults exhibited lower TA-SOL overlap (F_1,23 = 41.2, P < 0.001) and greater TA-SOL peak EMG delay (F_1,25 = 35.5, P < 0.001). This finding suggests that although subjects in both age groups displayed similar movement end points, they exhibited a different motor plan, as demonstrated by altered coordination between the agonist and antagonist muscles.NEW & NOTEWORTHY We aimed to determine whether the altered activation of muscles in older adults compared with young adults during fast goal-directed movements is related to an altered motor plan. For matched movements, there were differences in the coordination of antagonistic muscles but no differences in the individual activation of muscles. We provide novel evidence that the differential activation of muscles in older adults is related to an altered motor plan.

Footedness Is Associated with Self-reported Sporting Performance and Motor Abilities in the General Population

Left-handers may have strategic advantages over right-handers in interactive sports and innate superior abilities that are beneficial for sports. Previous studies relied on differing criteria for handedness classification and mostly did not investigate mixed preferences and footedness. Footedness appears to be less influenced by external and societal factors than handedness. Utilizing latent class analysis and structural equation modeling, we investigated in a series of studies (total N > 15300) associations of handedness and footedness with self-reported sporting performance and motor abilities in the general population. Using a discovery and a replication sample (ns = 7658 and 5062), Study 1 revealed replicable beneficial effects of mixed-footedness and left-footedness in team sports, martial arts and fencing, dancing, skiing, and swimming. Study 2 (n = 2592) showed that footedness for unskilled bipedal movement tasks, but not for skilled unipedal tasks, was beneficial for sporting performance. Mixed- and left-footedness had effects on motor abilities that were consistent with published results on better brain interhemispheric communication, but also akin to testosterone-induced effects regarding flexibility, strength, and endurance. Laterality effects were only small. Possible neural and hormonal bases of observed effects need to be examined in future studies.

Laterality and Plantar Pressure Distribution During Gait in Healthy Children: Comment on Mayolas Pi, Arrese, Aparicio, and Masià (2015)

In a recent paper, Mayolas Pi, Arrese, Aparicio, and Masià reported the absence of significant bilateral differences between legs in the average plantar pressure during walking in six- to seven-year-old children. However, the authors demonstrated bilateral differences in the distribution of plantar pressure during walking independent of foot preference in three tests: kicking a ball with precision, balancing on one foot, and jumping on one foot. From the results, Mayolas Pi et al. proposed that this asymmetric pattern of plantar pressure distribution is not caused by laterality. This paper suggests that the selected age range of participants and methods of diagnosing of laterality and data analysis could have significant effects on the results. Indeed, according to the literature, laterality in humans is a multidimensional trait with poor stabilization and conformity between different dimensions in preschool and younger school children.

Asymmetrical motor behaviour as a window to early leg preference: a longitudinal study in infants 7-12 months of age

This longitudinal study explored leg preference in infancy during half-kneel pulling-to-stand (PTS) and asymmetrical four-point kneeling, which is part of the typical motor repertoire of infants. The special characteristics of the half-kneel PTS as a discrete task, performed in a bilateral context provide the opportunity to explore leg preference during an asymmetrical behaviour. Twenty-seven infants were observed in their homes, every 3 weeks between the ages of 7-12 months. Leg preference was determined by the "lead-out" limb used as the infants pulled to stand from the half-kneeling position (half-kneel PTS). As a complementary measure, the leading leg during asymmetrical four-point kneeling and crawling ("asymmetrical four-point patterns") was used in the 10 infants who developed these patterns. The infants studied showed a general preference for using a leading leg during half-kneel PTS, which was mostly consistent over the study period. A strong correlation was found between leg preferences during half-kneel PTS and asymmetrical four-point patterns. The findings documented functional asymmetry in infant lower limbs during half-kneel PTS and asymmetrical four-point patterns, highlighting the importance of the tasks used to define leg preference.

Tactile Toe Agnosia and Percept of a "Missing Toe" in Healthy Humans

A disturbance of body representation is central to many neurological and psychiatric conditions, but the mechanisms by which body representations are constructed by the brain are not fully understood. We demonstrate a directional disturbance in tactile identification of the toes in healthy humans. Nineteen young adult participants underwent tactile stimulation of the digits with the eyes closed and verbally reported the identity of the stimulated digit. In the majority of individuals, responses to the second and third toes were significantly biased toward the laterally neighboring digit. The directional bias was greater for the nondominant foot and was affected by the identity of the immediately preceding stimulated toe. Unexpectedly, 9/19 participants reported the subjective experience of a "missing toe" or "missing space" during the protocol. These findings challenge current models of somatosensory localization, as they cannot be explained simply by a lack of distinct representations for toes compared with fingers, or by overt toe-finger correspondences. We present a novel theory of equal spatial representations of digit width combined with a "preceding neighbor" effect to explain the observed phenomena. The diagnostic implications for neurological disorders that involve "digit agnosia" are discussed.

Are there right hemisphere contributions to visually-guided movement? Manipulating left hand reaction time advantages in dextrals

Many studies have argued for distinct but complementary contributions from each hemisphere in the control of movements to visual targets. Investigators have attempted to extend observations from patients with unilateral left- and right-hemisphere damage, to those using neurologically-intact participants, by assuming that each hand has privileged access to the contralateral hemisphere. Previous attempts to illustrate right hemispheric contributions to the control of aiming have focussed on increasing the spatial demands of an aiming task, to attenuate the typical right hand advantages, to try to enhance a left hand reaction time advantage in right-handed participants. These early attempts have not been successful. The present study circumnavigates some of the theoretical and methodological difficulties of some of the earlier experiments, by using three different tasks linked directly to specialized functions of the right hemisphere: bisecting, the gap effect, and visuospatial localization. None of these tasks were effective in reducing the magnitude of left hand reaction time advantages in right handers. Results are discussed in terms of alternatives to right hemispheric functional explanations of the effect, the one-dimensional nature of our target arrays, power and precision given the size of the left hand RT effect, and the utility of examining the proportions of participants who show these effects, rather than exclusive reliance on measures of central tendency and their associated null hypothesis significance tests.

Surgical leg rotation: cortical neuroplasticity assessed through brain mapping using transcranial magnetic stimulation

Rotationplasty (Borggreve-Van Nes operation) is a rare limb salvage procedure, most often applied to children presenting with sarcoma of the distal femur. In type A1 operation, the distal thigh is removed and the proximal tibia is axially rotated by 180°, remodeled, grafted onto the femoral stump, and then prosthetized. The neurovascular bundle is spared. The rotated ankle then works as a knee. The foot plantar and dorsal flexors act as knee extensors and flexors, respectively. Functional results may be excellent. Cortical neuroplasticity was studied in three men (30–31 years) who were operated on the left lower limb at ages between 7 and 11 years and were fully autonomous with a custom-made prosthesis, as well as in three age–sex matched controls. The scalp stimulation coordinates, matching the patients’ brain MRI spots, were digitized through a ‘neuronavigation’ optoelectronic system, in order to guide the transcranial magnetic stimulation coil, thus ensuring spatial precision during the procedure. Through transcranial magnetic stimulation driven by neuronavigation, the cortical representations of the contralateral soleus and vastus medialis muscles were studied in terms of amplitude of motor evoked potentials (MEPs) and centering and width of the cortical areas from which the potentials could be evoked. Map centering on either hemisphere did not differ substantially across muscles and participants. In the operated patients, MEP amplitudes, the area from which MEPs could be evoked, and their product (volume) were larger for the muscles of the unaffected side compared with both the rotated soleus muscle (average effect size 0.75) and the muscles of healthy controls (average effect size 0.89). In controls, right–left differences showed an effect size of 0.38. In no case did the comparisons reach statistical significance (P>0.25). Nevertheless, the results seem consistent with cortical plasticity reflecting strengthening of the unaffected leg and a combination of cross-education and skill training of the rotated leg.

Novel diffusion tensor imaging technique reveals developmental streamline volume changes in the corticospinal tract associated with leg motor control

BACKGROUND

Diffusion tensor imaging (DTI) has expanded our knowledge of corticospinal tract (CST) anatomy and development. However, previous developmental DTI studies assessed the CST as a whole, overlooking potential differences in development of its components related to control of the upper and lower extremities. The present cross-sectional study investigated age-related changes, side and gender differences in streamline volume of the leg- and hand-related segments of the CST in children.

SUBJECTS AND METHODS

DTI data of 31 children (1-14 years; mean age: 6±4 years; 17 girls) with normal conventional MRI were analyzed. Leg- and hand-related CST streamline volumes were quantified separately, using a recently validated novel tractography approach. CST streamline volumes on both sides were compared between genders and correlated with age.

RESULTS

Higher absolute streamline volumes were found in the left leg-related CST compared to the right (p=0.001) without a gender effect (p=0.4), whereas no differences were found in the absolute hand-related CST volumes (p>0.4). CST leg-related streamline volumes, normalized to hemispheric white matter volumes, declined with age in the right hemisphere only (R=-.51; p=0.004). Absolute leg-related CST streamline volumes showed similar, but slightly weaker correlations. Hand-related absolute or normalized CST streamline volumes showed no age-related variations on either side.

CONCLUSION

These results suggest differential development of CST segments controlling hand vs. leg movements. Asymmetric volume changes in the lower limb motor pathway may be secondary to gradually strengthening left hemispheric dominance and is consistent with previous data suggesting that footedness is a better predictor of hemispheric lateralization than handedness.

Mixed-footedness is a more relevant predictor of schizotypy than mixed-handedness

Mixed-handedness was reported indicative of schizotypy, relevant to psychosis and schizophrenia. However, studies suffered from validity threats and did not systematically investigate associations with footedness. Moreover, there is a dearth of studies in the general population and it is currently untested whether widely used self-report scales measure schizotypy in a comparable way in student and community samples. The present study used two large and independent community and student samples (total N>2800) and utilized latent class analysis (LCA) for the classification of handedness and footedness. Psychometric properties and measurement equivalence of the Schizotypal Personality Questionnaire-Brief form (SPQ-B) in the two samples were also examined. We found that mixed-handedness (<6% prevalence), but also much more common mixed-footedness (25% prevalence), was specifically and similarly associated with higher schizotypy in both samples, Cohen d=0.15-0.18. Findings indicate that schizotypal traits in conjunction with mixed lateral preferences are thus more prevalent in the overall population than previously assumed, and that footedness may be the more relevant predictor of schizotypy than handedness. Findings are further consistent with evidence on neurodevelopmental instability, but also epigenetic mechanisms involving the sex chromosomes, regarding possible common causes of both mixed-handedness and psychosis-relevant traits.

Dominant side in single-leg stance stability during floor oscillations at various frequencies

Background

We investigated lateral dominance in the postural stability of single-leg stance with anteroposterior floor oscillations at various frequencies.

Methods

Thirty adults maintained a single-leg stance on a force platform for 20 seconds per trial. Trials were performed with no oscillation (static condition) and with anteroposterior floor oscillations (2.5-cm amplitude) at six frequencies: 0.25, 0.5, 0.75, 1.0, 1.25 and 1.5 Hz (dynamic condition). A set of three trials was performed on each leg in each oscillation frequency in random order. The mean speed of the center of pressure in the anteroposterior direction (CoP_ap) was calculated as an index of postural stability, and frequency analysis of CoP_ap sway was performed. Footedness for carrying out mobilizing activities was assessed with a questionnaire.

Results

CoP_ap speed exponentially increased as oscillation frequency increased in both legs. The frequency analysis of CoP_ap showed a peak <0.3 Hz at no oscillation. The frequency components at 0.25-Hz oscillation included common components with no oscillation and those at 1.5-Hz oscillation showed the maximum amplitude among all conditions. Postural stability showed no significant difference between left- and right-leg stance at no oscillation and oscillations ≤1.25 Hz, but at 1.5-Hz oscillation was significantly higher in the right-leg stance than in the left-leg stance. For the lateral dominance of postural stability at individual levels, the lateral difference in postural stability at no oscillation was positively correlated with that at 0.25-Hz oscillation (r = 0.51) and negatively correlated with that at 1.5-Hz oscillation (r = -0.53). For 70% of subjects, the dominant side of postural stability was different at no oscillation and 1.5-Hz oscillation. In the subjects with left- or right-side dominance at no oscillation, 94% or 38% changed their dominant side at 1.5-Hz oscillation, with a significant difference between these percentages. In the 1.5-Hz oscillation, 73% of subjects had concordance between the dominant side of postural stability and that of mobilizing footedness.

Conclusion

In static conditions, there was no lateral dominance of stability during single-leg stance. At 1.5-Hz oscillation, the highest frequency, right-side dominance of postural stability was recognized. Functional role in supporting leg may be divided between left and right legs according to the change of balance condition from static to dynamic.

Evidence for general right-, mixed-, and left-sidedness in self-reported handedness, footedness, eyedness, and earedness, and a primacy of footedness in a large-sample latent variable analysis

Lateral preferences are important for the study of cerebral lateralization and may be indicative of neurobehavioral disorders, neurodevelopmental instability, and deficits in lateralization. Previous studies showed that self-reported preferences are also concordantly interrelated, suggesting a common genetic or biological origin, sidedness. However, with regard to the assessment and classification of lateral preferences, there is a dearth of psychometric studies, but a need for psychometrically validated instruments that can be reliably used in applied research. Based on three independent large samples (total N>15,100), this study investigated the psychometric properties of widely-used lateral preference scales of handedness, footedness, eyedness, and earedness. Preferences were consistently and replicably categorical, consisting of right, mixed, and left preferences each, underlining that primarily qualitative, rather than quantitative, differences differentiate lateral preferences. Right-, mixed-, and left-sidedness underlay the individual preferences, but sidedness alone could not fully explain the observed inter-relations. Footedness was the single most important indicator of sidedness. Our data were further consistent with predictions of right shift theory and corroborated a 'pull-to-concordance' in hand-foot preferences. We recommend the use of psychometrically validated scales and of a trichotomous classification of lateral preferences in future research, but conclude that handedness may be a biased indicator of underlying sidedness. Footedness needs to be examined more closely with regard to cerebral lateralization, neurodevelopmental disorders, and neurodevelopmental instability.

FOXP2 variation modulates functional hemispheric asymmetries for speech perception

Left-hemispheric language dominance is a well-known characteristic of the human language system, but the molecular mechanisms underlying this crucial feature of vocal communication are still far from being understood. The forkhead box P2 gene FOXP2, which has been related to speech development, constitutes an interesting candidate gene in this regard. Therefore, the present study was aimed at investigating effects of variation in FOXP2 on individual language dominance. To this end, we used a dichotic listening and a visual half-field task in a sample of 456 healthy adults. The FOXP2 SNPs rs2396753 and rs12533005 were found to be significantly associated with the distribution of correct answers on the dichotic listening task. These results show that variation in FOXP2 may contribute to the inter-individual variability in hemispheric asymmetries for speech perception.

Hemifield or hemispace: what accounts for the ipsilateral advantages in visually guided aiming?

Aiming movements to targets presented on the same side as the reaching limb are faster and more accurate than movements made across the body. These advantages are typically attributed to within-hemisphere sensorimotor control. However, contrary to the within- versus between-hemisphere model, we have shown that some of these advantages tend to go with the side of the movement, rather than the side of the target (Carey et al. Exp Brain Res 112:496-504, 1996; Carey and Otto-de Haart Neuropsychologia 39:894, 2001). Barthélémy and Boulinghez (Exp Brain Res 147:305-312, 2002) acknowledge that our biomechanical account fits data for post-onset movement parameters such as peak velocity and duration, yet they report evidence for some within- versus between-hemisphere contributions to reaction time (RT) advantages. To examine a possible difference between early and late movement kinematics fitting these alternative models, we have dissociated field and space in a different way, which required arm movements with differential inertial consequences, as well as unpredictability of target location in terms of visual field. The data suggest that visual field may contribute some of the variance to hemispatial effects, but only for the right hand. In a second experiment, we used an antipointing task to examine hemispatial versus visual field effects on RTs and to revisit the possible hand difference identified in experiment 1. We found that hemispace accounted for all of the ipsilateral advantages, including RT, for both right and left hands. Results are discussed in terms of the computational requirements of eye-hand coordination in relative unconstrained conditions.

An examination of handedness and footedness in children with high functioning autism and Asperger syndrome

Motor control deficits have been documented in children with high functioning autism and Asperger syndrome (HFA/AS), but the extent to which these disorders affect the children's footedness must be delineated. Twelve typically developing (TD) children and 12 children with HFA/AS, ages 6-9 years, were recruited. Motor control skills were assessed through a variety of footedness tasks to determine location and nature of impairment, regarding motor dominance. Overall, greater inconsistencies in dominance arose in children with HFA/AS, through disparities in measures of preference. Results will have broader implications for understanding motor impairments in children with HFA/AS as determined by comparing performance on footedness tasks, as well as for the design of interventions to account for these deficits.

Selective Interference of Finger Movements on Basic Addition and Subtraction Problem Solving

Fingers offer a practical tool to represent and manipulate numbers during the acquisition of arithmetic knowledge, usually with a greater involvement in addition and subtraction than in multiplication. In adults, brain-imaging studies show that mental arithmetic increases activity in areas known for their contribution to finger movements. It is unclear, however, if this truly reflects functional interactions between the processes and/or representations controlling finger movements and those involved in mental arithmetic, or a mere anatomical proximity. In this study we assessed whether finger movements interfere with basic arithmetic problem solving, and whether this interference is specific for the operations that benefit the most from finger-based calculation strategies in childhood. In Experiment 1, we asked participants to solve addition, subtraction, and multiplication problems either with their hands at rest or while moving their right-hand fingers sequentially. The results showed that finger movements induced a selective time cost in solving addition and subtraction but not multiplication problems. In Experiment 2, we asked participants to solve the same problems while performing a sequence of foot movements. The results showed that foot movements produced a nonspecific interference with all three operations. Taken together, these findings demonstrate the specific role of finger-related processes in solving addition and subtraction problems, suggesting that finger movements and mental arithmetic are functionally related.