Marietta Papadatou-Pastou

Sex Differences in Left-Handedness : A Meta-Analysis of 144 Studies

Human handedness, a marker for language lateralization in the brain, continues to attract great research interest. A widely reported but not universal finding is a greater male tendency toward left-handedness. Here the authors present a meta-analysis of k = 144 studies, totaling N = 1,787,629 participants, the results of which demonstrate that the sex difference is both significant and robust. The overall best estimate for the male to female odds ratio was 1.23 (95% confidence interval = 1.19, 1.27). The widespread observation of this sex difference is consistent with it being related to innate characteristics of sexual differentiation, and its observed magnitude places an important constraint on current theories of handedness. In addition, the size of the sex difference was significantly moderated by the way in which handedness was assessed (by writing hand or by other means), the location of testing, and the year of publication of the study, implicating additional influences on its development.

An efficient and reliable method for measuring cerebral lateralization during speech with functional transcranial Doppler ultrasound.

The gold standard method for measuring cerebral lateralization, the Wada technique, is too invasive for routine research use. Functional magnetic resonance imaging is a viable alternative but it is costly and affected by muscle artefact when activation tasks involve speech. Functional transcranial Doppler ultrasonography (fTCD) can be used to assess cerebral lateralization by comparing blood flow in the middle cerebral arteries. We used fTCD to compare indices of language lateralization in 33 adults in three different paradigms: Word Generation, Picture Description and a shorter Animation Description task. Animation Description gave valid results, and we subsequently demonstrated its reliability in a group of 21 4-year-old children. Cerebral lateralization during spoken language generation can be assessed reliably and cheaply using fTCD with a paradigm that is less taxing than the traditional word generation paradigm, does not require literacy skills and can be completed in 15 min or less.

Patterns of Individual Differences in Conceptual Understanding and Arithmetical Skill: A Meta-Analysis

Some theories from cognitive psychology and mathematics education suggest that childrens understanding of mathematical concepts develops together with their knowledge of mathematical procedures. However, previous research into childrens understanding of the inverse relationship between addition and subtraction suggests that there are individual differences in the way that this concept develops. To determine whether these differences are reliable and reflect alternative paths of development, we examined data from 14 studies of childrens understanding of inversion. Cluster analyses and meta-analytic techniques were used to quantify the size of the inversion effect and examine factors influencing its size and to test the stability of patterns of individual differences across the studies. Evidence was found for reliable patterns of individual differences, which have implications for current theories of concept development.

Single dose antidepressant administration modulates the neural processing of self-referent personality trait words.

Drugs which inhibit the re-uptake of monoamines in the brain are effective in the treatment of depression; however, the neuropsychological mechanisms which lead to the resolution of depressive symptomatology are unclear. Behavioral studies in healthy volunteers suggest that acute administration of the selective norepinephrine reuptake inhibitor reboxetine modulates emotional processing. The current study therefore explored the neural basis of this effect. A single dose of reboxetine (4 mg) or placebo was administered to 24 healthy volunteers in a double-blind between-group design. Neural responses during categorisation and recognition of self-referent personality trait words were assessed using event-related functional Magnetic Resonance Imaging (fMRI). Reboxetine had no effect on neuronal response during self-referent categorisation of positive or negative personality trait words. However, in a subsequent memory test, reboxetine reduced neuronal activation in a fronto-parietal network during correct recognition of positive target words vs. matched distractors. This was combined with increased speed to recognize positive vs. negative words compared to control subjects and suggests facilitated memory for positive self-referent material. These results support the hypothesis that antidepressants have early effects on the neural processing of emotional material which may be important in their therapeutic actions.

Intelligence and handedness: Meta-analyses of studies on intellectually disabled, typically developing, and gifted individuals.

Understanding the relationship between cerebral laterality and intelligence is important in elucidating the neurological underpinnings of individual differences in cognitive abilities. A widely used, behavioral indicator for cerebral laterality, mainly of language, is handedness. A number of studies have compared cognitive abilities between groups of left- and right-handers, while others have investigated the handedness prevalence between groups of different cognitive abilities. The present study comprises five meta-analyses of studies that have assessed the handedness prevalence in (a) individuals with intellectual disability (ID) of unknown/idiopathic nature compared to typically developing (TD) individuals, and (b) individuals with intellectual giftedness (IG) compared to TD individuals. Nineteen data sets totaling 16,076 participants (5795 ID, 8312 TD, and 1969 IG) were included in the analyses. Elevated levels of atypical handedness were found to be robust only for the ID to TD comparison. Findings constrain the range of acceptable theories on the handedness distribution for different intelligence levels.

Sex and Location as Determinants of Handedness: Reply to Vuoksimaa and Kaprio (2010).

In response to the comment by Vuoksimaa and Kaprio (2010) on our previous article on sex differences in left-handedness (Papadatou-Pastou, Martin, Munafò, and Jones, 2008), we carried out an additional meta-analysis to explore whether the widely observed tendency for rates of left-handedness to be greater among male than female individuals is also found in Scandinavian (Nordic) studies. The overall male-to-female ratio for left- to right-handedness odds provides evidence in favor of this hypothesis. However, the results were subject to a significant moderating effect related to nation of origin. We discuss the potential impact on observed measures of additive rather than multiplicative processes that may underlie sex differences in handedness and also the date-of-study effect on handedness rates.

Handedness prevalence in the deaf: Meta-analyses

An under-investigated aspect of handedness, a biological proxy for cerebral laterality for language, is its prevalence amongst deaf individuals. We present four sets of meta-analyses on studies measuring handedness prevalence in deaf individuals, comprising 31 data sets and totaling 5,392 participants (4,606 deaf, 786 hearing). Deaf individuals were found to be 2.61 times more likely to be non-right-handed and 2.25 times more likely to be left-handed compared to their hearing counterparts. When handedness was measured by means of manipulative actions, the weighted estimates of handedness prevalence for deaf populations were 17.70% and 14.70% for non-right- and left-handedness respectively; when handedness was measured by means of sign actions, the prevalence was 10.60% and 9.70%, respectively. Yet, when comparing studies that measured handedness in the same deaf individuals using both manipulative and sign actions, no difference was found in their handedness prevalence. This pattern is taken to suggest that the higher prevalence of atypical handedness in the deaf population may be linked to delayed language acquisition.

Improving the School Learning Environment to Reduce Bullying: An Experimental Study.

A framework based on research on bullying and on educational effectiveness was offered to schools to assist them in developing strategies and actions to improve their learning environment, their policy for teaching, and their evaluation mechanisms in order to reduce bullying. At the beginning and end of the intervention, the Revised Olweus Bully/Victim Questionnaire and a teacher questionnaire measuring three school factors (school policy for teaching, school learning environment, and school evaluation) were administered to the experimental and control groups. This experimental study reveals that the intervention had both a direct impact on the reduction of bullying and an indirect impact through improving the school factors. Implications for research into supporting schools to reduce bullying are given.

Right-handers have negligibly higher IQ scores than left-handers: Systematic review and meta-analyses

HighlightsSystematic review of 36 studies (66,108 individuals) measuring full IQ scores.Three sets of meta‐analyses including data on 20,442 individuals.Marginal differences in mean IQ scores detected between right‐ and left‐handers.Negligible difference in favor of right‐handers. ABSTRACT The relationship between intelligence and handedness remains a matter of debate. The present study is a systematic review of 36 studies (totaling 66,108 individuals), which have measured full IQ scores in different handedness groups. Eighteen of those studies were further included in three sets of meta‐analyses (totaling 20,442 individuals), which investigated differences in standardized mean IQ scores in (i) left‐handers, (ii) non‐right‐handers, and (iii) mixed‐handers compared to right‐handers. The bulk of the studies included in the systematic review reported no differences in IQ scores between left‐ and right‐handers. In the meta‐analyses, statistically significant differences in mean IQ scores were detected between right‐handers and left‐handers, but were marginal in magnitude (d = −0.07); the data sets were found to be homogeneous. Significance was lost when the largest study was excluded. No differences in mean IQ scores were found between right‐handers and non‐right‐handers as well as between right‐handers and mixed‐handers. No sex differences were found. Overall, the intelligence differences between handedness groups in the general population are negligible.

Salivary testosterone levels are unrelated to handedness or cerebral lateralization for language

ABSTRACT Behavioural and cerebral lateralization are thought to be controlled, at least in part, by prenatal testosterone (T) levels, explaining why sex differences are found in both laterality traits. The present study investigated hormonal effects on laterality using adult salivary T levels, to explore the adequacy of competing theories: the Geschwind, Behan and Galaburda, the callosal, and the sexual differentiation hypotheses. Sixty participants (15 right-handers and 15 left-handers of each sex) participated. Behavioural lateralization was studied by means of hand preference tests (i.e., the Edinburgh Handedness Inventory and the Quantification of Hand Preference test) and a hand skill test (i.e., the Peg-Moving test) whereas cerebral lateralization for language was studied using the Consonant-Vowel Dichotic Listening test and the Visual Half-Field Lexical Decision test. Salivary T and cortisol (C) concentrations were measured by luminescence immunoassay. Canonical correlations did not reveal significant relationships between T levels and measures of hand preference, hand skill, or language laterality. Thus, our findings add to the growing literature showing no relationship between T concentrations with behavioural or cerebral lateralization. It is claimed that prenatal T is not a major determinant of individual variability in either behavioural or cerebral lateralization.