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PubMed1991

Effects of handedness and sex on the morphology of the corpus callosum: a study with brain magnetic resonance imaging.

In view of conflicting data in the existing literature, we examined 53 normal subjects using a handedness questionnaire and callosal area measurements obtained from midsagittal MRI images. The callosum was found to be significantly larger in nonconsistent right-handers (NCRH), especially in its anterior half and especially for males. A significant hand x sex interaction, favoring consistent right-handed (CRH) females, was also found for the posterior midbody, a region known to house interhemispheric fibers connecting the right and left posterior association cortices. These results (1) confirm Witelson's (1985) first findings on postmortem specimens; (2) validate a dichotomy between CRH and NCRH rather than simply considering the writing hand, as was the case in most other similar studies; and (3) suggest that at least two different sex-related--probably hormonal--factors may be acting during the callosal development, one explaining the larger anterior half in NCRH males and the other the larger posterior midbody in CRH females.

Adolescent↗
PubMed1992

Family handedness as a predictor of mental rotation ability among minority girls in a math-science training program.

Right-handed girls from nonright-handed families outperformed the other groups of minority adolescent girls enrolled in a science and technology program on a test of mental rotation ability. This target group excelled over right-handed girls with all right-handed relatives and nonright-handers. The pattern of group differences in mental rotation ability found here is consistent with those found for women with math-science training at the college level. The minority boys in the program outperformed the girls as a whole, but did not differ significantly from the right-handed girls with nonright-handed relatives. The present findings provide further support for the generality of Annett's genetic theory of handedness and brain organization, and for the interaction of genetic and environmental factors in accounting for individual differences in mental rotation ability.

Achievement↗
PubMed1991

Reversal of 'handedness' in rats is achieved more effectively by training under peripheral than under central blockade of the preferred forepaw.

Reversal of forepaw preference was studied in rats under conditions of peripheral (bracelet) or central (inactivation of contralateral motor cortex and caudate nucleus by intracerebral injection of tetrodotoxin) preferred limb block. Persisting change of the forepaw preferred when reaching for food into a tubular feeder was achieved on the average after 91 (n = 27) and 211 (n = 26) reaches, respectively. When tested in another task (recovering food pellets from a horizontal shelf accessible through a narrow slit below the ceiling of the test box) same rats displayed identical (45%) and opposite (15%) preference or were ambidextrous (40%). Forced change of handedness on the tubular feeder task was accompanied by similar change of preference on the shelf task in only 17% rats. It is concluded that rather independent lateralisation of the two tasks reflects differential contribution of the corticospinal, rubrospinal and ventromedial motor systems. Reversal training proceeds faster with peripheral blockade which establishes not only the new preference but also inhibits the original one.

Animals↗
PubMed1992

Autoimmune thyroid disease, left-handedness, and developmental dyslexia.

Autoimmune thyroid disease (ATD) (Graves' disease and Hashimoto's thyroiditis) has been one of a number of autoimmune diseases possibly associated with left-handedness, mixed dominance, and learning disability. In the present study, 74 men with ATD were compared to 24 control men with non-ATD. An increased frequency of mixed dominance and traits suggestive of dyslexia were observed in the patients with ATD. These data are consistent with a link between the development of ATD and cerebral dominance.

Adult↗
PubMed1996

Actigraphic evaluation of handedness.

The utility of an objective evaluation of motor activity, actigraphy, was examined in the evaluation of handedness. Hand preference was assessed in a homogeneous group of 190 young volunteers using the Edinburgh Inventory (EI). The EI distribution obtained in the population studied was comparable with distributions cited in the literature. Simultaneous actigraphic recordings from both wrists were made in 58 of these subjects for 20 h, starting at 1000 h, using an epoch length of 4 s. Care was taken to include comparable numbers of right- and left-handers (based on EI score) in this subgroup. Two actigraphic parameters were defined. One of these, the Activity Index (AI[x]), is a measure of the difference in total motor activity between right and left wrist. The other, Movement Index (MIy[x]) is a measure of the difference in movement pattern. AI[x] showed a moderate but significant correlation with EI (r = 0.36, P < 0.005). The correlation between MIy[x] and EI was high (r = 0.65, P < 0.0001). Rebinning of the data into 60 s epochs decreased the degree of linear correlation between MIy[x] and EI. We conclude, in contrast to a previous study, that actigraphy can be used to discriminate between dominant and non-dominant hands; that the difference in movement pattern between right and left hand is larger than the difference in total motor activity; and that epoch lengths shorter than the conventional 60 s are more sensitive for this kind of discrimination.

Adult↗
PubMed2006

Handedness-related asymmetry in coupling strength in bimanual coordination: furthering theory and evidence.

The effects of handedness on bimanual isofrequency coordination (e.g., phase advance of the dominant limb) have been suggested to result from an asymmetry in interlimb coupling strength, with the non-dominant limb being more strongly influenced by the dominant limb than vice versa. A formalized version of this hypothesis was tested by examining the phase adjustments in both limbs in response to mechanical perturbation of the bimanual coordination pattern and during frequency-induced phase transitions, for both right- and left-handed participants. In both situations, the phase adaptations were made predominantly by the non-dominant limb in right-handers, whereas this effect failed to reach significance in left-handers. Thus, the asymmetry in coupling strength was less pronounced in the latter group. In addition, the degree of asymmetry depended on movement frequency. The observed asymmetry was discussed in relation to pertinent neurophysiological findings.

Adult↗
PubMed2004

Does handedness influence the strength of phantom limb illusions in the virtual reality box?

Subjects had to judge the size of a tactile stimulus held in the unseen hand, while a visible phantom hand representing that unseen hand held a tactile stimulus of same or different size. No asymmetries in interference effects were found that could be related to hand or handedness. The method lends itself to quantification of virtual reality box illusions and can be used to evaluate the role of experience and sources of variability in the strength of the illusion across subjects.

Computer Simulation↗
PubMed2006

Corpus callosum size is linked to dichotic deafness and hemisphericity, not sex or handedness.

Individuals differ in the number of corpus callosum (CC) nerve fibers interconnecting their cerebral hemispheres by about threefold. Early reports suggested that males had smaller CCs than females. This was often interpreted to support the concept that the male brain is more "lateralized" or "specialized," thus accounting for presumed male predominance in mathematics, as well as for aggressive behavior. Ultimately, meta-analyses of these many reports found no significant overall sex differences in inter-cerebral information carrying capacity. Here, using quantitative MRI, we found the midline CC area of 113 subjects was significantly correlated, not with handedness or sex, but with dichotic deafness, and even more so with redefined hemisphericity, the latter accounting for over 19% of CC variability. That is, both dichotic hearing and right brain-oriented individuals of either sex had significantly larger CCs than dichotically deaf or left brain-oriented persons. Thus, current traditions of brain laterality and gender may benefit from revisions that include redefined hemisphericity.

Adolescent↗
PubMed2005

The genetic basis of hair whorl, handedness, and other phenotypes.

Evidence is presented that RHD, RHCE, and other RH genes, may be interesting candidates to consider when searching for the genetic basis of hair whorl rotation (i.e., clockwise or counterclockwise), handedness (i.e., right handed, left handed or ambidextrous), speech laterality (i.e., right brained or left brained), speech dyslexia (e.g., stuttering), sexual orientation (i.e., heterosexual, homosexual, bisexual, or transsexual), schizophrenia, bipolar disorder, and autism spectrum disorder. Such evidence involves the need for a genetic model that includes maternal immunization to explain some of the empirical results reported in the literature. The complex polymorphisms present among the maternally immunizing RH genes can then be used to explain other empirical results. Easily tested hypotheses are suggested, based upon genotypic (but not phenotypic) frequencies of the RH genes. In particular, homozygous dominant individuals are expected to be less common or lacking entirely among the alternative phenotypes. If it is proven that RH genes are involved in brain architecture, it will have a profound effect upon our understanding of the development and organization of the asymmetrical vertebrate brain and may eventually lead to a better understanding of the developmental processes which occur to produce the various alternative phenotypes discussed here. In addition, if RH genes are shown to be involved in the production of these phenotypes, then the evolutionary studies can be performed to demonstrate the beneficial effect of the recessive alleles of RHD and RHCE, and why human evolution appears to be selecting for the recessive alleles even though an increase in the frequency of such alleles may imply lower average fecundity among some individuals possessing them.

Chromosome Mapping↗
PubMed2003

The influence of handedness and gender on the microstructure of the human corpus callosum: a diffusion-tensor magnetic resonance imaging study.

The aim of the present study was to examine whether handedness and gender are associated with microstructural differences in human corpus callosum (CC). For this purpose, diffusion-tensor magnetic resonance imaging (DTI) was performed on 34 right- and 33 left-handed subjects of both sexes. Four quantitative variables (Mean Diffusion, Relative Anisotropy, parallel and orthogonal diffusion) were computed within the CC. A significantly increased anisotropy was found in left- as compared to right-handed subjects, and in men as compared to women. Additionally, both overall and orthogonal diffusion were significantly lower in left- than in right-handed subjects. Possible interpretations of these findings are discussed. The novel DTI technique promises to further advance current understanding of morphological structure in the living brain.

Adult↗
PubMed2005

Finger tapping, handedness and grey matter amount in the Rolando's genu area.

The morphology of the central sulcus (CS), at the level of the hand primary motor cortex, has been shown to be related to hand preference and skill. Differences in the cerebral functional organisation of left and right-handers have been described, notably with respect to hemispheric specialisation, which might cause the neural substrate of hand dominance or skill to differ between the two groups. Here, we further explored the relationship between the anatomical variability of the central sulcus and hand skill in two groups of young male subjects differing by handedness (n = 56 right-handers and n = 55 left-handers). Grey matter volume (GMV) in the upper region of the central sulcus was estimated with Voxel Based Morphometry, using a probabilistic region of interest approach, while hand motor skill was measured with the finger tapping test. No significant anatomical differences could be evidenced between the two hand preference groups, a rightward hemispheric asymmetry being observed in both samples. However, multiple regression analyses showed that, in the right-handed group, the maximum tapping rate of the right hand correlated positively with the left central sulcus GMV, but negatively with the right. Similar analyses showed that, in left-handers, the maximum tapping rate of the non-dominant right hand was strongly correlated with the GMV of the ipsilateral CS but not significantly with that of the contralateral CS. These results may be due to differences in the organisation of motor systems between these two groups, possibly concerning a left hemispheric specialisation for fast repetitive movements in right-handers, which would be different in left-handers.

Adult↗
PubMed2005

Handedness and cerebral anatomical asymmetries in young adult males.

Using voxel-based morphometry, we measured the cerebral anatomical asymmetries in a sample of 56 young right-handed males and then compared voxelwise asymmetry indices of these subjects to those of 56 young left-handed males. In the right-handed, the clusters of grey matter asymmetry corresponding to the leftward occipital petalia and planum temporale asymmetries were retrieved. Strong rightward temporo-parietal asymmetries were also observed, but the rightward grey matter asymmetry in the frontal lobe was less massive than previously described. Group comparisons of left- and right-handed subjects' asymmetry maps, performed at a statistical threshold not corrected for multiple comparisons, revealed significant effects of handedness on this pattern of anatomical asymmetry in frontal regions, notably in the lower central and precentral sulci, and also in the planum temporale, with right-handed subjects being more leftward asymmetric. Concerning white matter, although almost no focal differences between left- and right-handed subjects were detected, volumetric analyses at the hemispheric level revealed a leftward asymmetry, which happened to be significantly less marked in the left-handed. This latter result, together with the pattern of leftward white matter asymmetries, suggested that anatomical correlates of the left hemispheric specialization for language would exist in white matter. In the population we studied, differences in anatomical asymmetry between left- and right-handed subjects provided structural arguments for a greater functional ambilaterality in left-handed subjects.

Adolescent↗
PubMed2004

Cross-modal recognition of shape from hand to eyes and handedness in human newborns.

The present research addresses the question of the generality of the ability to transfer shape information from one hand to the eyes recently evidenced in human newborns. Using an intersensory paired-preference procedure, we confirmed that newborns can visually recognize the shape of an object that they have previously manipulated with their right hand, out of sight. However, the results revealed that this ability is absent when the left hand is involved. Handedness in cross-modal transfer task is discussed in relation to other behavioral asymmetries in newborns. Taken together, the present research confirms the existence in some conditions of an early fragile ability to extract shape information in a tactual format and transfer it to a visual format, independent of common experience.

Analysis of Variance↗
PubMed2004

Effects of handedness on tactile temporal order judgment.

We examined effects of handedness on the judgment of temporal order of successive taps delivered to both hands. When the subjects' arms were uncrossed, the temporal resolution (84% correct responses) of right-handed subjects (52 +/- 4 ms, n = 16) was significantly better than that of left-handed subjects (83 +/- 9 ms, n = 16). When their arms were crossed, both groups tended to invert their judgment to a similar extent at intervals as long as 200-300 ms. In the arms crossed condition, right handed subjects inverted their judgment more often in response to left-hand-first stimuli than to right-hand-first stimuli, whereas left-handed subjects did not show the same asymmetry. We infer that hemispheric lateralization, which is generally stronger in right- than in left-handed subjects, contributes to the relatively better temporal resolution of right-handed subjects in the uncrossed condition, as well as to the asymmetric effect of stimulation order in the crossed condition.

Adolescent↗
PubMed1991

Handedness effects in the detection of dichotically-presented words and emotions.

Left-handed and right-handed subjects were given two dichotic listening tasks using identical material. In one task, they were asked to determine whether or not a specific target word was present (verbal task). In the other task, subjects were asked to indicate whether or not one of the dichotically-competing words was spoken in a particular affective tone (emotion task). Overall, a right-ear advantage (REA) was found with the verbal task and a left-ear advantage (LEA) with the emotion task. Left-handers showed a slightly smaller REA than right-handers on the verbal task, but a slightly larger LEA on the emotion task. This finding suggests that left- and right-hemispheric functions are not related in a complementary fashion and that handedness effects for nonverbal tasks are different from those seen with verbal tasks. The emotional LEA was much larger for angry stimuli than for happy, sad, or neutral stimuli. Rather than providing evidence for a hemisphere by affective valence interaction, such results suggest a stimulus-specific effect.

Adult↗
PubMed1978

The handedness of rhesus monkeys: II. Concurrent reaching.

Of 171 monkeys tested for handedness, 60 were found to make occasional bilateral concurrent reaches. These reaches accounted for only 1.3% of the total of 600 reaches observed for each animal. Younger animals were observed to make such reaches more frequently than older animals. Concurrent reaching was characterized by a lower degree of preference for the overall preferred hand than unilateral reaches made by the same animals at comparable periods of testing.

Animals↗
PubMed1978

Handedness and intelligence.

The scores of 37 right and 30 left-handed subjects on tests of fluid and crystallized intelligence were compared. Consistent with the hypothesis, it was found that the left-handers were inferior to the right-handers on the Gf task. These data are consistent with those from three earlier studies and serve to question the assertion that there are no handedness related differences in ability.

Functional Laterality↗
PubMed1979

An evaluation of the Briggs-Nebes modified version of Annett's handedness inventory.

The Briggs-Nebes (1975) modified version of Annett's (1967) handedness inventory was administered to 59 female and 51 male undergraduates and 101 nursing students. J-shaped distributions of scores in the dextral direction and significant sex differences such that males were more sinistral than females were found. The inventory was found to be multi-dimensional with up to three factors, power, skill, and rhythm in order of importance. The utility of the modified inventory was supported and recommendations were made concerning the use of subscale or factor scores in addition to overall scores.

Factor Analysis, Statistical↗