Hand preference for writing and associations with selected demographic and behavioral variables in 255,100 subjects: the BBC internet study

Crossed cerebral lateralization for verbal and visuo-spatial function in a pair of handedness discordant monozygotic twins: MRI and fMRI brain imaging

To examine the nature of hemispheric lateralization for neural processes underlying verbal fluency and visuo-spatial attention, we investigated a single pair of handedness discordant monozygotic (MzHd) twins. Imaging of the brain was undertaken using magnetic resonance imaging (MRI) and functional magnetic resonance imaging (fMRI) in combination with manual performance tasks. The twins were discordant for MRI anatomical asymmetries of the pars triangularis and planum temporale, whose asymmetry was consistent with verbal laterality on fMRI. Thus, the right-handed twin had left lateralized verbal with right lateralized visuo-spatial attention, while the left-handed twin had right lateralized verbal with left lateralized visuo-spatial activation; these data lend further support for to the conclusions of Sommer et al.

Handedness and intellectual achievement: an even-handed look

Evidence from a large-scale study of 11-year olds in Britain suggests that ambidextrous individuals may be disadvantaged in tests of verbal, nonverbal, reading, and mathematical skills relative to right- and left-handers, but this basic finding was not replicated in another study of younger boys in Germany. Here, we present data based on a television show in which members of the public were given an IQ test. Some individuals were also asked to state whether they wrote with the left hand, right hand, or either hand. The data support the earlier finding that ambidextrous individuals perform more poorly than left- or right-handers, especially on subscales measuring arithmetic, memory, and reasoning, and extend that finding to adults.

Callosal misconnectivity and the sex difference in psychosis

The sex difference in age of onset in schizophrenia is paradoxical in the sense that the brain is developing faster in females but onsets are earlier in males. Therefore if schizophrenia, as widely believed, is a disorder of development, the difference is in the wrong direction. Here we attempt to resolve the paradox with the hypothesis that psychosis is an anomaly of development of cerebral asymmetry and the following assumptions: (1) asymmetry (the torque) confers directionality on the 'language circuit'--failure to develop asymmetry leads to the risk of reverse transmission, a putative mechanism of psychotic symptoms; (2) the corpus callosum goes on developing in an antero-posterior direction into the third and fourth decades of life; (3) a sex difference in structure and development of the corpus callosum (with some anterior components greater in males and posterior components greater in females) reflects stronger, faster lateralization in females; (4) because of the inverse relationship between asymmetry and interhemispheric connections, females, by developing faster, avoid the misconnectivity phenomena in the frontal lobes that males, developing more slowly, may encounter at a younger age with particular risk of negative symptoms.

Mixed-handedness is associated with the reporting of psychotic-like beliefs in a non-clinical Italian sample

Atypical handedness has been repeatedly reported in schizophrenia, with quantitative review of evidence showing an increase of non-right-handedness in patients diagnosed with schizophrenia. Mixed-handedness is also higher among non-clinical people scoring high on questionnaires aimed at measuring psychosis-proneness. However, the greatest part of information on non-clinical samples came from samples collected in North America or in the UK: differences by countries in the socio-cultural pressure to use the right hand could influence the results. In this study 604 Italian non-clinical participants (248 males, 41.1%; 356 females, 58.9%; mean age=34.5+/-11.9) completed the Annett Hand Preference Questionnaire (HPQ), the General Health Questionnaire (GHQ), and the Peters et al. Delusions Inventory (PDI). In the sample, 527 subjects (87.3%) were classified on the HPQ as right-handed, 53 (8.8%) were classified as mixed-handed, and 24 (4.0%) were classified as left-handed. Mixed-handed scored statistically higher on the PDI than the right-handed and left-handed, but right-handed and left-handed did not differ from each other on a statistical ground. The difference by handedness was specific for PDI, since scores on the GHQ-12 did not differ by handedness group. The links between mixed-handedness and psychosis-proneness in non-clinical samples are a reliable finding, deserving further investigation as a model for the risk of schizophrenia.

The BBC internet study: general methodology

This article provides an overview of a large-scale web-based survey, commissioned by the British Broadcasting Corporation (BBC), designed to investigate sex differences. I describe the background and challenges inherent to Web-based testing, the history and rationale behind this study, the design and implementation, and ethical and methodological considerations in the research design. I also discuss the kinds of data collected from around 255,000 participants, describe basic demographic information about the BBC sample, and examine reliability and validity, both internally and in comparison with other similar studies. I conclude that the dataset was largely reliable, and merits the analyses described later in this special section.

Determination of hemispheric emotional valence in individual subjects: a new approach with research and therapeutic implications

BACKGROUND

Much has been theorized about the emotional properties of the hemispheres. Our review of the dominant hypotheses put forth by Schore, Joseph, Davidson, and Harmon-Jones on hemispheric emotional valences (HEV) shows that none are supported by robust data. Instead, we propose that individual's hemispheres are organized to have differing HEVs that can be lateralized in either direction.

METHODS

Probe auditory evoked potentials (AEP) recorded during a neutral and an upsetting memory were used to assess HEV in 28 (20 F) right-handed subjects who were either victims of childhood maltreatment (N = 12) or healthy controls. In a sub-population, we determined HEV by emotional response to lateral visual field stimulation (LVFS), in which vision is limited to one, then the other hemifield. We compare a number of morphometric and functional brain measures between individuals who have right-negative versus left-negative HEV.

RESULTS

Using AEPs to determine HEV, we found 62% of controls and 67% of maltreated subjects had right negative HEV. There was a strong interaction between HEV-laterality and gender, which together accounted for 60% of individual variability in total grey matter volume (GMV). HEV-laterality was associated with differences in hippocampal volume, amygdala/hippocampal ratios, and measures of verbal, visual and global memory. HEV-laterality was associated also with different constellations of symptoms comparing maltreated subjects to controls. Emotional response to LVFS provided a convenient and complementary measure of HEV-laterality that correlated significantly with the HEVs determined by AEPs.

CONCLUSION

Our findings suggest that HEV-laterality, like handedness or gender, is an important individual difference with significant implications for brain and behavioral research, and for guiding lateralized treatments such as rTMS.

Association of Digit Ratio (2D:4D) with Self-Reported Attractiveness in Men and Women

Abstract. Prenatal testosterone (PT) may influence attractiveness such that high PT increases attractiveness in men. Here we are concerned with self-perceptions of attractiveness, rather than ratings of attractiveness by others. Our sample was 255,116 participants drawn from an Internet survey. We considered the relationship between self-reported attractiveness and the ratio of the length of the 2nd and 4th digits (digit ratio, 2D:4D), a putative negative correlate of PT. Participants reported ratings on their general attractiveness, and the attractiveness of their face, voice, and body. There were significant effects of sexual orientation on the ratings and we considered only heterosexuals in all subsequent analyses. We found that 2D:4D was negatively correlated with general, facial, and body attractiveness, with the strongest association for body attractiveness. There was no relationship for voice attractiveness. General, facial, and body attractiveness were negatively associated with age and positively related to height (a possible correlate of adult testosterone, AT). However, the 2D:4D relationships were independent of age and height. 2D:4D differs across ethnic groups, but a consideration of only white Caucasians gave essentially the same results. We conclude that (1) high PT, as measured by low 2D:4D, is associated with self-perception of high attractiveness in men and women, and (2) the relationships between height and attractiveness indicate that AT is also positively correlated to self-perceptions of attractiveness in men and women. Thus, high PT and AT may increase body esteem in both men and women.