Gender, laterality, learning difficulties and health problems

Relationship between the order of permanent tooth eruption and the predominance of motor function laterality: a cross-sectional study

OBJECTIVES

To assess whether the order of permanent tooth eruption may be a useful indicator of motor function laterality.

METHODS

We conducted a cross-sectional study in schoolchildren aged 6-8 years old evaluated in the annual school-based routine dental health examinations conducted by the staff of the primary care centre of an urban district in Barcelona, Spain. We also evaluated hand, foot, eye, and auditory lateralities using a battery of simple exercises. Bivariate and multivariate analysis of data was performed.

RESULTS

The study sample included 388 children, 51.3% female, with a mean age of 6.5 years. Right laterality was the predominant side in every variable under study, especially in tooth eruption (310 children; 80%), handedness (349; 89.9%), and footedness (337; 86.8%). In the bivariate analysis, we found a statistically significant association of tooth eruption laterality with handedness and footedness, and of tooth eruption laterality with ocular and auditory lateralities (p<.001). In the multivariate analysis, tooth eruption laterality and foot laterality were independent variables significantly associated with hand laterality. The diagnostic accuracy of tooth eruption laterality and foot laterality in relation to hand laterality as reference, showed a similar sensitivity and positive and negative predictive values, but the specificity of dentition laterality was higher (79% versus 66%).

CONCLUSIONS

Laterality in the order of dental eruption is a useful indicator of right or left motor function laterality in developing individuals that may be particularly helpful to determine the main dominance in cases of crossed laterality.

Crossed Eye/Hand Laterality and Left-Eyedness Predict a Positive 24-Month Outcome in Alcohol-Dependent Patients

BACKGROUND

Available predictors of hospital readmission following withdrawal in alcohol-dependent patients are limited. However, such parameters are needed to optimize individualized treatment strategies. This study investigated whether crossed eye/hand laterality, eyedness, and handedness may predict outcomes in alcohol dependence.

METHODS

The prospective study included 200 early-abstinent alcohol-dependent inpatients (n[males] = 113, n[females] = 87) and 240 control subjects (n[males] = 133, n[females] = 107). We assessed eyedness and handedness using the hole-in-the-card and Shimizu tests and documented alcohol-related readmissions over 12 and 24 months.

RESULTS

Crossed eye/hand laterality and left-eyedness were associated with a reduced risk for alcohol-related readmission (12-month: odds ratios [OR] = 0.41, p = 0.008, OR = 0.42, p = 0.004; 24-month: OR = 0.57, p = 0.097, OR = 0.47, p = 0.016), fewer median readmissions (12-month: 0 vs. 1, p = 0.005, 0 vs. 1, p = 0.005; 24-month: 1 vs. 2, p = 0.014, 1 vs. 2, p = 0.006), and more mean days to the first readmission (12-month: 270 vs. 209, p = 0.007, 269 vs. 207, p = 0.003; 24-month: 462 vs. 335, p = 0.039, 461 vs. 323, p = 0.005). They also interacted with treatment and alcohol drinking history to predict the outcome. In sex-specific analyses, most of these effects remained significant in males but not in females. Handedness alone did not significantly predict outcome. Moreover, the laterality markers did not significantly differ between alcohol-dependent patients and control subjects.

CONCLUSIONS

Determining crossed eye/hand laterality and eyedness may help to individualize relapse prevention in the future. Both are easily accessible predictors of alcohol-related readmission following inpatient withdrawal treatment.

Effects of eye dominance (left vs. right) and cannabis use on intermanual coordination and negative symptoms in schizophrenia patients

Based on the previous findings, it has been assumed that in schizophrenia patients, eye dominance and cannabis use will affect negative symptoms and intermanual coordination (IMC), an index of interhemispheric communication. But eye dominance, specifically the clinical findings for it, has been neglected in schizophrenia research. We therefore investigated its effects in 52 right-handed (36 right-eyed and 16 left-eyed) and 51 left-handed (35 left-eyed and 16 right-eyed) schizophrenia in-patients without and with drug use. Eye dominance affected IMC in all schizophrenia patients. When comparing right- and left-handers, we found that this result was only significant in the right-handed patients and in the smaller subgroup without drug use. In the right-handers, left eye dominance-like left-handedness-was associated with higher values in IMC and less pronounced manifestation of negative symptoms, right eye dominance was not. Thus, left-eyed right-handers may be more closely related to left-handers than to right-handers. In accordance with the results from the literature, we suggest that these findings are due to better interhemispheric connections and less impairment of white matter structures, especially in right-hemispheric regions. Moreover, cannabis use was related to higher scores in IMC and less pronounced negative symptoms, but only in the right-eyed and not in the left-eyed right-handers or in the left-handers. Hence, differences in eye dominance and handedness may be partially responsible for different results in interhemispheric connections among cannabis users. In conclusion, both eye dominance and use of cannabis should be taken into account when assessing clinical symptoms in schizophrenia patients.

Effect of handedness on the Stroop Colour Word Task

Handedness is associated with cerebral organisation, but its relationship with cognition remains unclear. Since the Stroop task is believed to measure aspects of executive control, this study aims to investigate the effect of handedness on Stroop interference. We used the Stroop task with 90 young adults with university education, of whom 47 (23 males) were right-handed and 43 (21 males) were left-handed. Main dependent variables were Stroop baseline (SB), Stroop incongruent (SI), and the proportional derivative Stroop reduction (SR) [SR=(SB - SI)/SB×100%] (Bugg, Delosh, Davalos, & Davis, 2007; Graf, Uttl, &Tuokko, 1995) scores. The analysis revealed that SI is significantly affected by both handedness and the interaction of sex×handedness, whereas SR is only affected by handedness. After controlling for the effect of SB on SI, only the effect of handedness remained statistically significant [F(1, 83) = 6.44, p=.013]. Post-hoc comparisons showed that left-handed females performed significantly better than right-handed females on both SI (p=.003) and SR (p=.007). The data suggest that handedness is associated with cognitive function alterations, which lead to a smaller Stroop interference of left-handers irrespectively of sex, an effect that is more pronounced in the female subpopulation.

Handedness in patients with developmental coordination disorder

Developmental coordination disorder affects 5% to 8% of the general population, and about 50% to 60% of these children have a comorbid attention-deficit disorder with hyperactivity and learning disorders. Left-handedness is relatively common among children with dyslexia, learning disabilities, and autism; however, its frequency in children with developmental coordination disorder is less clear. The present study investigated the distribution of hand dominance in 98 children (age range, 5.5-17 years) with developmental coordination disorder compared with their parents or siblings. Thirty children (30.6%) were left-handed and 13 (13.3%) were ambidextrous. The prevalence of left-handedness among their parents and siblings was similar to that of the general population. The results suggest that children with developmental coordination disorder, like children with learning disorders and deficit disorder with hyperactivity, present with higher frequency of left-hand dominance compared with the general population.

Handedness and health: An examination of the association between different handedness classifications and health disorders

The current study investigated the incidence of various health disorders in a sample population of undergraduate students, using a 25-item hand preference questionnaire. Analysis revealed significant differences existed in the incidence of several health disorders as a function of handedness: however, these differences depended on how hand preference was defined. Overall, the results showed that non-right-handed participants (i.e., those individuals with left-handed, ambidextrous, or inconsistent hand preferences) were significantly more likely to report specific health disorders (such as high blood pressure and epilepsy) than right-handed participants. The findings provide support for the argument that left-handedness, or non-right-handedness, is associated with various health disorders. The results are discussed in light of the Geschwind-Behan-Galaburda model of cerebral lateralisation.

Evaluation of empirical methods and methodological foundations of human left-handedness

The methodological and empirical foundations underlying the theories on human left-handedness are examined, including the definition and classification of left-handedness, its relation to pathology, and the results on family, adoption, and twin research. It is argued that major research findings on left-handedness are based on inadequate empirical methods, and the concrete definitions and assessment procedures do not meet validity and reliability criteria. This also casts doubt on the relationship between left-handedness and pathology reported in the literature. Furthermore, findings from family, adoption, and twin studies do not allow interpretation of possible direct genetic contributions to explaining left-handedness. It is concluded that the methodological limitations of a causal explanation should encourage an examination of the epistemological and methodological premises of theory formulation. The functional method and a theoretical framework based on early childhood experiences and the neural plasticity of the brain may be more appropriate for the selection of empirical methods in research of human left-handedness.

Associations among familial sinistrality, allergies, and developmental language disorders

Here we report the results of a study that tested what has become known as the Geschwind hypothesis (Geschwind & Galaburda, 1987). This study involved 526 people who were tested by an allergist for IgE-mediated allergies and who filled out a 12-item handedness questionnaire that also included questions about eyedness, prevalence of left-handedness in the immediate family, and familial developmental language problems. A series of log-linear analyses revealed that if the definition of "anomalous" included left-handedness and having a first-order left-handed relative, one was indeed more likely to be allergic than were those not so classified. When the definition of anomalous simply included those classified as left-handed, the results were not significant. Parallel findings resulted when the criterion variable was the presence of developmental language disorders. No evidence was found for relations between allergies and developmental language problems.

[Ontogenesis of lateralities. A review and attempted interpretation]

The present paper offers an updated review on lateralization development in normal children. Instead of just citing a voluminous litterature, we prefer to present an interpretation which perhaps is too synthetic but which tries to go beyond the frequent contradictions encountered within experimental studies as well as between the studies themselves. Results plead for a double movement in the human development, first towards a species-specific asymmetry, then towards a differentiated symmetry. We propose different advantages for the development of human competencies and for the underlying neuro-behavioural organization: asymmetry corresponds to phases in the intrahemispheric cerebral organization and symmetry to phases of interhemispheric synergy.